refine error handling in prometheus (#5388)

i) Uses the more idiomatic Wrap and Wrapf methods for creating nested errors.
ii) Fixes some incorrect usages of fmt.Errorf where the error messages don't have any formatting directives.
iii) Does away with the use of fmt package for errors in favour of pkg/errors

Signed-off-by: tariqibrahim <tariq181290@gmail.com>

cmd/prometheus/main.go

@@ -35,23 +35,23 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	conntrack "github.com/mwitkow/go-conntrack"
 	"github.com/oklog/oklog/pkg/group"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/common/promlog"
 	"github.com/prometheus/common/version"
-	prom_runtime "github.com/prometheus/prometheus/pkg/runtime"
+	kingpin "gopkg.in/alecthomas/kingpin.v2"
-	"gopkg.in/alecthomas/kingpin.v2"
 	"k8s.io/klog"
 
-	"github.com/mwitkow/go-conntrack"
-	"github.com/prometheus/common/promlog"
 	promlogflag "github.com/prometheus/common/promlog/flag"
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/discovery"
 	sd_config "github.com/prometheus/prometheus/discovery/config"
 	"github.com/prometheus/prometheus/notifier"
 	"github.com/prometheus/prometheus/pkg/relabel"
+	prom_runtime "github.com/prometheus/prometheus/pkg/runtime"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/rules"
 	"github.com/prometheus/prometheus/scrape"
@@ -439,7 +439,7 @@ func main() {
 				fs, err := filepath.Glob(pat)
 				if err != nil {
 					// The only error can be a bad pattern.
-					return fmt.Errorf("error retrieving rule files for %s: %s", pat, err)
+					return errors.Wrapf(err, "error retrieving rule files for %s", pat)
 				}
 				files = append(files, fs...)
 			}
@@ -600,7 +600,7 @@ func main() {
 				}
 
 				if err := reloadConfig(cfg.configFile, logger, reloaders...); err != nil {
-					return fmt.Errorf("error loading config from %q: %s", cfg.configFile, err)
+					return errors.Wrapf(err, "error loading config from %q", cfg.configFile)
 				}
 
 				reloadReady.Close()
@@ -650,7 +650,7 @@ func main() {
 					&cfg.tsdb,
 				)
 				if err != nil {
-					return fmt.Errorf("opening storage failed: %s", err)
+					return errors.Wrapf(err, "opening storage failed")
 				}
 				level.Info(logger).Log("msg", "TSDB started")
 				level.Debug(logger).Log("msg", "TSDB options",
@@ -682,7 +682,7 @@ func main() {
 		g.Add(
 			func() error {
 				if err := webHandler.Run(ctxWeb); err != nil {
-					return fmt.Errorf("error starting web server: %s", err)
+					return errors.Wrapf(err, "error starting web server")
 				}
 				return nil
 			},
@@ -734,7 +734,7 @@ func reloadConfig(filename string, logger log.Logger, rls ...func(*config.Config
 
 	conf, err := config.LoadFile(filename)
 	if err != nil {
-		return fmt.Errorf("couldn't load configuration (--config.file=%q): %v", filename, err)
+		return errors.Wrapf(err, "couldn't load configuration (--config.file=%q)", filename)
 	}
 
 	failed := false
@@ -745,7 +745,7 @@ func reloadConfig(filename string, logger log.Logger, rls ...func(*config.Config
 		}
 	}
 	if failed {
-		return fmt.Errorf("one or more errors occurred while applying the new configuration (--config.file=%q)", filename)
+		return errors.Errorf("one or more errors occurred while applying the new configuration (--config.file=%q)", filename)
 	}
 	promql.SetDefaultEvaluationInterval(time.Duration(conf.GlobalConfig.EvaluationInterval))
 	level.Info(logger).Log("msg", "Completed loading of configuration file", "filename", filename)
@@ -782,7 +782,7 @@ func computeExternalURL(u, listenAddr string) (*url.URL, error) {
 	}
 
 	if startsOrEndsWithQuote(u) {
-		return nil, fmt.Errorf("URL must not begin or end with quotes")
+		return nil, errors.New("URL must not begin or end with quotes")
 	}
 
 	eu, err := url.Parse(u)

cmd/promtool/archive.go

@@ -16,8 +16,9 @@ package main
 import (
 	"archive/tar"
 	"compress/gzip"
-	"fmt"
 	"os"
+
+	"github.com/pkg/errors"
 )
 
 const filePerm = 0644
@@ -31,7 +32,7 @@ type tarGzFileWriter struct {
 func newTarGzFileWriter(archiveName string) (*tarGzFileWriter, error) {
 	file, err := os.Create(archiveName)
 	if err != nil {
-		return nil, fmt.Errorf("error creating archive %q: %s", archiveName, err)
+		return nil, errors.Wrapf(err, "error creating archive %q", archiveName)
 	}
 	gzw := gzip.NewWriter(file)
 	tw := tar.NewWriter(gzw)

cmd/promtool/http.go

@@ -15,10 +15,10 @@ package main
 
 import (
 	"context"
-	"fmt"
 	"net/http"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/api"
 )
 
@@ -34,7 +34,7 @@ func newPrometheusHTTPClient(serverURL string) (*prometheusHTTPClient, error) {
 		Address: serverURL,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("error creating HTTP client: %s", err)
+		return nil, errors.Wrapf(err, "error creating HTTP client")
 	}
 	return &prometheusHTTPClient{
 		requestTimeout: defaultTimeout,

cmd/promtool/main.go

@@ -26,15 +26,15 @@ import (
 	"strings"
 	"time"
 
-	"gopkg.in/alecthomas/kingpin.v2"
-
 	"github.com/google/pprof/profile"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/api"
-	"github.com/prometheus/client_golang/api/prometheus/v1"
+	v1 "github.com/prometheus/client_golang/api/prometheus/v1"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/version"
+	kingpin "gopkg.in/alecthomas/kingpin.v2"
+
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/pkg/rulefmt"
 	"github.com/prometheus/prometheus/util/promlint"
@@ -202,10 +202,10 @@ func checkConfig(filename string) ([]string, error) {
 		// If an explicit file was given, error if it is not accessible.
 		if !strings.Contains(rf, "*") {
 			if len(rfs) == 0 {
-				return nil, fmt.Errorf("%q does not point to an existing file", rf)
+				return nil, errors.Errorf("%q does not point to an existing file", rf)
 			}
 			if err := checkFileExists(rfs[0]); err != nil {
-				return nil, fmt.Errorf("error checking rule file %q: %s", rfs[0], err)
+				return nil, errors.Wrapf(err, "error checking rule file %q", rfs[0])
 			}
 		}
 		ruleFiles = append(ruleFiles, rfs...)
@@ -213,7 +213,7 @@ func checkConfig(filename string) ([]string, error) {
 
 	for _, scfg := range cfg.ScrapeConfigs {
 		if err := checkFileExists(scfg.HTTPClientConfig.BearerTokenFile); err != nil {
-			return nil, fmt.Errorf("error checking bearer token file %q: %s", scfg.HTTPClientConfig.BearerTokenFile, err)
+			return nil, errors.Wrapf(err, "error checking bearer token file %q", scfg.HTTPClientConfig.BearerTokenFile)
 		}
 
 		if err := checkTLSConfig(scfg.HTTPClientConfig.TLSConfig); err != nil {
@@ -247,17 +247,17 @@ func checkConfig(filename string) ([]string, error) {
 
 func checkTLSConfig(tlsConfig config_util.TLSConfig) error {
 	if err := checkFileExists(tlsConfig.CertFile); err != nil {
-		return fmt.Errorf("error checking client cert file %q: %s", tlsConfig.CertFile, err)
+		return errors.Wrapf(err, "error checking client cert file %q", tlsConfig.CertFile)
 	}
 	if err := checkFileExists(tlsConfig.KeyFile); err != nil {
-		return fmt.Errorf("error checking client key file %q: %s", tlsConfig.KeyFile, err)
+		return errors.Wrapf(err, "error checking client key file %q", tlsConfig.KeyFile)
 	}
 
 	if len(tlsConfig.CertFile) > 0 && len(tlsConfig.KeyFile) == 0 {
-		return fmt.Errorf("client cert file %q specified without client key file", tlsConfig.CertFile)
+		return errors.Errorf("client cert file %q specified without client key file", tlsConfig.CertFile)
 	}
 	if len(tlsConfig.KeyFile) > 0 && len(tlsConfig.CertFile) == 0 {
-		return fmt.Errorf("client key file %q specified without client cert file", tlsConfig.KeyFile)
+		return errors.Errorf("client key file %q specified without client cert file", tlsConfig.KeyFile)
 	}
 
 	return nil
@@ -510,7 +510,7 @@ func parseTime(s string) (time.Time, error) {
 	if t, err := time.Parse(time.RFC3339Nano, s); err == nil {
 		return t, nil
 	}
-	return time.Time{}, fmt.Errorf("cannot parse %q to a valid timestamp", s)
+	return time.Time{}, errors.Errorf("cannot parse %q to a valid timestamp", s)
 }
 
 type endpointsGroup struct {

cmd/promtool/unittest.go

@@ -24,7 +24,8 @@ import (
 	"strings"
 	"time"
 
-	"gopkg.in/yaml.v2"
+	"github.com/pkg/errors"
+	yaml "gopkg.in/yaml.v2"
 
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/promql"
@@ -84,7 +85,7 @@ func ruleUnitTest(filename string) []error {
 	groupOrderMap := make(map[string]int)
 	for i, gn := range unitTestInp.GroupEvalOrder {
 		if _, ok := groupOrderMap[gn]; ok {
-			return []error{fmt.Errorf("group name repeated in evaluation order: %s", gn)}
+			return []error{errors.Errorf("group name repeated in evaluation order: %s", gn)}
 		}
 		groupOrderMap[gn] = i
 	}
@@ -261,14 +262,14 @@ func (tg *testGroup) test(mint, maxt time.Time, evalInterval time.Duration, grou
 				}
 
 				if gotAlerts.Len() != expAlerts.Len() {
-					errs = append(errs, fmt.Errorf("    alertname:%s, time:%s, \n        exp:%#v, \n        got:%#v",
+					errs = append(errs, errors.Errorf("    alertname:%s, time:%s, \n        exp:%#v, \n        got:%#v",
 						testcase.Alertname, testcase.EvalTime.String(), expAlerts.String(), gotAlerts.String()))
 				} else {
 					sort.Sort(gotAlerts)
 					sort.Sort(expAlerts)
 
 					if !reflect.DeepEqual(expAlerts, gotAlerts) {
-						errs = append(errs, fmt.Errorf("    alertname:%s, time:%s, \n        exp:%#v, \n        got:%#v",
+						errs = append(errs, errors.Errorf("    alertname:%s, time:%s, \n        exp:%#v, \n        got:%#v",
 							testcase.Alertname, testcase.EvalTime.String(), expAlerts.String(), gotAlerts.String()))
 					}
 				}
@@ -284,7 +285,7 @@ Outer:
 		got, err := query(suite.Context(), testCase.Expr, mint.Add(testCase.EvalTime),
 			suite.QueryEngine(), suite.Queryable())
 		if err != nil {
-			errs = append(errs, fmt.Errorf("    expr:'%s', time:%s, err:%s", testCase.Expr,
+			errs = append(errs, errors.Errorf("    expr:'%s', time:%s, err:%s", testCase.Expr,
 				testCase.EvalTime.String(), err.Error()))
 			continue
 		}
@@ -301,7 +302,7 @@ Outer:
 		for _, s := range testCase.ExpSamples {
 			lb, err := promql.ParseMetric(s.Labels)
 			if err != nil {
-				errs = append(errs, fmt.Errorf("    expr:'%s', time:%s, err:%s", testCase.Expr,
+				errs = append(errs, errors.Errorf("    expr:'%s', time:%s, err:%s", testCase.Expr,
 					testCase.EvalTime.String(), err.Error()))
 				continue Outer
 			}
@@ -318,7 +319,7 @@ Outer:
 			return labels.Compare(gotSamples[i].Labels, gotSamples[j].Labels) <= 0
 		})
 		if !reflect.DeepEqual(expSamples, gotSamples) {
-			errs = append(errs, fmt.Errorf("    expr:'%s', time:%s, \n        exp:%#v, \n        got:%#v", testCase.Expr,
+			errs = append(errs, errors.Errorf("    expr:'%s', time:%s, \n        exp:%#v, \n        got:%#v", testCase.Expr,
 				testCase.EvalTime.String(), parsedSamplesString(expSamples), parsedSamplesString(gotSamples)))
 		}
 	}
@@ -397,7 +398,7 @@ func query(ctx context.Context, qs string, t time.Time, engine *promql.Engine, q
 			Metric: labels.Labels{},
 		}}, nil
 	default:
-		return nil, fmt.Errorf("rule result is not a vector or scalar")
+		return nil, errors.New("rule result is not a vector or scalar")
 	}
 }
 

config/config.go

@@ -22,13 +22,14 @@ import (
 	"strings"
 	"time"
 
-	"github.com/prometheus/prometheus/pkg/labels"
+	"github.com/pkg/errors"
-	"github.com/prometheus/prometheus/pkg/relabel"
-
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
+	yaml "gopkg.in/yaml.v2"
+
 	sd_config "github.com/prometheus/prometheus/discovery/config"
-	"gopkg.in/yaml.v2"
+	"github.com/prometheus/prometheus/pkg/labels"
+	"github.com/prometheus/prometheus/pkg/relabel"
 )
 
 var (
@@ -59,7 +60,7 @@ func LoadFile(filename string) (*Config, error) {
 	}
 	cfg, err := Load(string(content))
 	if err != nil {
-		return nil, fmt.Errorf("parsing YAML file %s: %v", filename, err)
+		return nil, errors.Wrapf(err, "parsing YAML file %s", filename)
 	}
 	resolveFilepaths(filepath.Dir(filename), cfg)
 	return cfg, nil
@@ -234,14 +235,14 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 
 	for _, rf := range c.RuleFiles {
 		if !patRulePath.MatchString(rf) {
-			return fmt.Errorf("invalid rule file path %q", rf)
+			return errors.Errorf("invalid rule file path %q", rf)
 		}
 	}
 	// Do global overrides and validate unique names.
 	jobNames := map[string]struct{}{}
 	for _, scfg := range c.ScrapeConfigs {
 		if scfg == nil {
-			return fmt.Errorf("empty or null scrape config section")
+			return errors.New("empty or null scrape config section")
 		}
 		// First set the correct scrape interval, then check that the timeout
 		// (inferred or explicit) is not greater than that.
@@ -249,7 +250,7 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 			scfg.ScrapeInterval = c.GlobalConfig.ScrapeInterval
 		}
 		if scfg.ScrapeTimeout > scfg.ScrapeInterval {
-			return fmt.Errorf("scrape timeout greater than scrape interval for scrape config with job name %q", scfg.JobName)
+			return errors.Errorf("scrape timeout greater than scrape interval for scrape config with job name %q", scfg.JobName)
 		}
 		if scfg.ScrapeTimeout == 0 {
 			if c.GlobalConfig.ScrapeTimeout > scfg.ScrapeInterval {
@@ -260,18 +261,18 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		}
 
 		if _, ok := jobNames[scfg.JobName]; ok {
-			return fmt.Errorf("found multiple scrape configs with job name %q", scfg.JobName)
+			return errors.Errorf("found multiple scrape configs with job name %q", scfg.JobName)
 		}
 		jobNames[scfg.JobName] = struct{}{}
 	}
 	for _, rwcfg := range c.RemoteWriteConfigs {
 		if rwcfg == nil {
-			return fmt.Errorf("empty or null remote write config section")
+			return errors.New("empty or null remote write config section")
 		}
 	}
 	for _, rrcfg := range c.RemoteReadConfigs {
 		if rrcfg == nil {
-			return fmt.Errorf("empty or null remote read config section")
+			return errors.New("empty or null remote read config section")
 		}
 	}
 	return nil
@@ -302,10 +303,10 @@ func (c *GlobalConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 
 	for _, l := range gc.ExternalLabels {
 		if !model.LabelName(l.Name).IsValid() {
-			return fmt.Errorf("%q is not a valid label name", l.Name)
+			return errors.Errorf("%q is not a valid label name", l.Name)
 		}
 		if !model.LabelValue(l.Value).IsValid() {
-			return fmt.Errorf("%q is not a valid label value", l.Value)
+			return errors.Errorf("%q is not a valid label value", l.Value)
 		}
 	}
 
@@ -315,7 +316,7 @@ func (c *GlobalConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		gc.ScrapeInterval = DefaultGlobalConfig.ScrapeInterval
 	}
 	if gc.ScrapeTimeout > gc.ScrapeInterval {
-		return fmt.Errorf("global scrape timeout greater than scrape interval")
+		return errors.New("global scrape timeout greater than scrape interval")
 	}
 	if gc.ScrapeTimeout == 0 {
 		if DefaultGlobalConfig.ScrapeTimeout > gc.ScrapeInterval {
@@ -381,7 +382,7 @@ func (c *ScrapeConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if len(c.JobName) == 0 {
-		return fmt.Errorf("job_name is empty")
+		return errors.New("job_name is empty")
 	}
 
 	// The UnmarshalYAML method of HTTPClientConfig is not being called because it's not a pointer.
@@ -411,12 +412,12 @@ func (c *ScrapeConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 
 	for _, rlcfg := range c.RelabelConfigs {
 		if rlcfg == nil {
-			return fmt.Errorf("empty or null target relabeling rule in scrape config")
+			return errors.New("empty or null target relabeling rule in scrape config")
 		}
 	}
 	for _, rlcfg := range c.MetricRelabelConfigs {
 		if rlcfg == nil {
-			return fmt.Errorf("empty or null metric relabeling rule in scrape config")
+			return errors.New("empty or null metric relabeling rule in scrape config")
 		}
 	}
 
@@ -447,7 +448,7 @@ func (c *AlertingConfig) UnmarshalYAML(unmarshal func(interface{}) error) error
 
 	for _, rlcfg := range c.AlertRelabelConfigs {
 		if rlcfg == nil {
-			return fmt.Errorf("empty or null alert relabeling rule")
+			return errors.New("empty or null alert relabeling rule")
 		}
 	}
 	return nil
@@ -507,7 +508,7 @@ func (c *AlertmanagerConfig) UnmarshalYAML(unmarshal func(interface{}) error) er
 
 	for _, rlcfg := range c.RelabelConfigs {
 		if rlcfg == nil {
-			return fmt.Errorf("empty or null Alertmanager target relabeling rule")
+			return errors.New("empty or null Alertmanager target relabeling rule")
 		}
 	}
 
@@ -524,7 +525,7 @@ func (c *AlertmanagerConfig) UnmarshalYAML(unmarshal func(interface{}) error) er
 func CheckTargetAddress(address model.LabelValue) error {
 	// For now check for a URL, we may want to expand this later.
 	if strings.Contains(string(address), "/") {
-		return fmt.Errorf("%q is not a valid hostname", address)
+		return errors.Errorf("%q is not a valid hostname", address)
 	}
 	return nil
 }
@@ -561,11 +562,11 @@ func (c *RemoteWriteConfig) UnmarshalYAML(unmarshal func(interface{}) error) err
 		return err
 	}
 	if c.URL == nil {
-		return fmt.Errorf("url for remote_write is empty")
+		return errors.New("url for remote_write is empty")
 	}
 	for _, rlcfg := range c.WriteRelabelConfigs {
 		if rlcfg == nil {
-			return fmt.Errorf("empty or null relabeling rule in remote write config")
+			return errors.New("empty or null relabeling rule in remote write config")
 		}
 	}
 
@@ -623,7 +624,7 @@ func (c *RemoteReadConfig) UnmarshalYAML(unmarshal func(interface{}) error) erro
 		return err
 	}
 	if c.URL == nil {
-		return fmt.Errorf("url for remote_read is empty")
+		return errors.New("url for remote_read is empty")
 	}
 	// The UnmarshalYAML method of HTTPClientConfig is not being called because it's not a pointer.
 	// We cannot make it a pointer as the parser panics for inlined pointer structs.

discovery/azure/azure.go

@@ -29,6 +29,7 @@ import (
 	"github.com/Azure/go-autorest/autorest/azure"
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 
@@ -76,7 +77,7 @@ type SDConfig struct {
 
 func validateAuthParam(param, name string) error {
 	if len(param) == 0 {
-		return fmt.Errorf("azure SD configuration requires a %s", name)
+		return errors.Errorf("azure SD configuration requires a %s", name)
 	}
 	return nil
 }
@@ -107,7 +108,7 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	}
 
 	if c.AuthenticationMethod != authMethodOAuth && c.AuthenticationMethod != authMethodManagedIdentity {
-		return fmt.Errorf("unknown authentication_type %q. Supported types are %q or %q", c.AuthenticationMethod, authMethodOAuth, authMethodManagedIdentity)
+		return errors.Errorf("unknown authentication_type %q. Supported types are %q or %q", c.AuthenticationMethod, authMethodOAuth, authMethodManagedIdentity)
 	}
 
 	return nil
@@ -227,7 +228,7 @@ func newAzureResourceFromID(id string, logger log.Logger) (azureResource, error)
 	// /subscriptions/SUBSCRIPTION_ID/resourceGroups/RESOURCE_GROUP/providers/PROVIDER/TYPE/NAME/TYPE/NAME
 	s := strings.Split(id, "/")
 	if len(s) != 9 && len(s) != 11 {
-		err := fmt.Errorf("invalid ID '%s'. Refusing to create azureResource", id)
+		err := errors.Errorf("invalid ID '%s'. Refusing to create azureResource", id)
 		level.Error(logger).Log("err", err)
 		return azureResource{}, err
 	}
@@ -243,12 +244,12 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 
 	client, err := createAzureClient(*d.cfg)
 	if err != nil {
-		return nil, fmt.Errorf("could not create Azure client: %s", err)
+		return nil, errors.Wrap(err, "could not create Azure client")
 	}
 
 	machines, err := client.getVMs(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("could not get virtual machines: %s", err)
+		return nil, errors.Wrap(err, "could not get virtual machines")
 	}
 
 	level.Debug(d.logger).Log("msg", "Found virtual machines during Azure discovery.", "count", len(machines))
@@ -256,13 +257,13 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 	// Load the vms managed by scale sets.
 	scaleSets, err := client.getScaleSets(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("could not get virtual machine scale sets: %s", err)
+		return nil, errors.Wrap(err, "could not get virtual machine scale sets")
 	}
 
 	for _, scaleSet := range scaleSets {
 		scaleSetVms, err := client.getScaleSetVMs(ctx, scaleSet)
 		if err != nil {
-			return nil, fmt.Errorf("could not get virtual machine scale set vms: %s", err)
+			return nil, errors.Wrap(err, "could not get virtual machine scale set vms")
 		}
 		machines = append(machines, scaleSetVms...)
 	}
@@ -342,7 +343,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 						}
 						// If we made it here, we don't have a private IP which should be impossible.
 						// Return an empty target and error to ensure an all or nothing situation.
-						err = fmt.Errorf("unable to find a private IP for VM %s", vm.Name)
+						err = errors.Errorf("unable to find a private IP for VM %s", vm.Name)
 						ch <- target{labelSet: nil, err: err}
 						return
 					}
@@ -357,7 +358,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 	var tg targetgroup.Group
 	for tgt := range ch {
 		if tgt.err != nil {
-			return nil, fmt.Errorf("unable to complete Azure service discovery: %s", err)
+			return nil, errors.Wrap(err, "unable to complete Azure service discovery")
 		}
 		if tgt.labelSet != nil {
 			tg.Targets = append(tg.Targets, tgt.labelSet)
@@ -371,7 +372,7 @@ func (client *azureClient) getVMs(ctx context.Context) ([]virtualMachine, error)
 	var vms []virtualMachine
 	result, err := client.vm.ListAll(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("could not list virtual machines: %s", err.Error())
+		return nil, errors.Wrap(err, "could not list virtual machines")
 	}
 	for result.NotDone() {
 		for _, vm := range result.Values() {
@@ -379,7 +380,7 @@ func (client *azureClient) getVMs(ctx context.Context) ([]virtualMachine, error)
 		}
 		err = result.NextWithContext(ctx)
 		if err != nil {
-			return nil, fmt.Errorf("could not list virtual machines: %s", err.Error())
+			return nil, errors.Wrap(err, "could not list virtual machines")
 		}
 	}
 
@@ -390,13 +391,13 @@ func (client *azureClient) getScaleSets(ctx context.Context) ([]compute.VirtualM
 	var scaleSets []compute.VirtualMachineScaleSet
 	result, err := client.vmss.ListAll(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("could not list virtual machine scale sets: %s", err.Error())
+		return nil, errors.Wrap(err, "could not list virtual machine scale sets")
 	}
 	for result.NotDone() {
 		scaleSets = append(scaleSets, result.Values()...)
 		err = result.NextWithContext(ctx)
 		if err != nil {
-			return nil, fmt.Errorf("could not list virtual machine scale sets: %s", err.Error())
+			return nil, errors.Wrap(err, "could not list virtual machine scale sets")
 		}
 	}
 
@@ -409,12 +410,12 @@ func (client *azureClient) getScaleSetVMs(ctx context.Context, scaleSet compute.
 	r, err := newAzureResourceFromID(*scaleSet.ID, nil)
 
 	if err != nil {
-		return nil, fmt.Errorf("could not parse scale set ID: %s", err)
+		return nil, errors.Wrap(err, "could not parse scale set ID")
 	}
 
 	result, err := client.vmssvm.List(ctx, r.ResourceGroup, *(scaleSet.Name), "", "", "")
 	if err != nil {
-		return nil, fmt.Errorf("could not list virtual machine scale set vms: %s", err.Error())
+		return nil, errors.Wrap(err, "could not list virtual machine scale set vms")
 	}
 	for result.NotDone() {
 		for _, vm := range result.Values() {
@@ -422,7 +423,7 @@ func (client *azureClient) getScaleSetVMs(ctx context.Context, scaleSet compute.
 		}
 		err = result.NextWithContext(ctx)
 		if err != nil {
-			return nil, fmt.Errorf("could not list virtual machine scale set vms: %s", err.Error())
+			return nil, errors.Wrap(err, "could not list virtual machine scale set vms")
 		}
 	}
 

discovery/config/config.go

@@ -14,7 +14,7 @@
 package config
 
 import (
-	"fmt"
+	"github.com/pkg/errors"
 
 	"github.com/prometheus/prometheus/discovery/azure"
 	"github.com/prometheus/prometheus/discovery/consul"
@@ -64,62 +64,62 @@ type ServiceDiscoveryConfig struct {
 func (c *ServiceDiscoveryConfig) Validate() error {
 	for _, cfg := range c.AzureSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in azure_sd_configs")
+			return errors.New("empty or null section in azure_sd_configs")
 		}
 	}
 	for _, cfg := range c.ConsulSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in consul_sd_configs")
+			return errors.New("empty or null section in consul_sd_configs")
 		}
 	}
 	for _, cfg := range c.DNSSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in dns_sd_configs")
+			return errors.New("empty or null section in dns_sd_configs")
 		}
 	}
 	for _, cfg := range c.EC2SDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in ec2_sd_configs")
+			return errors.New("empty or null section in ec2_sd_configs")
 		}
 	}
 	for _, cfg := range c.FileSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in file_sd_configs")
+			return errors.New("empty or null section in file_sd_configs")
 		}
 	}
 	for _, cfg := range c.GCESDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in gce_sd_configs")
+			return errors.New("empty or null section in gce_sd_configs")
 		}
 	}
 	for _, cfg := range c.KubernetesSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in kubernetes_sd_configs")
+			return errors.New("empty or null section in kubernetes_sd_configs")
 		}
 	}
 	for _, cfg := range c.MarathonSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in marathon_sd_configs")
+			return errors.New("empty or null section in marathon_sd_configs")
 		}
 	}
 	for _, cfg := range c.NerveSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in nerve_sd_configs")
+			return errors.New("empty or null section in nerve_sd_configs")
 		}
 	}
 	for _, cfg := range c.OpenstackSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in openstack_sd_configs")
+			return errors.New("empty or null section in openstack_sd_configs")
 		}
 	}
 	for _, cfg := range c.ServersetSDConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in serverset_sd_configs")
+			return errors.New("empty or null section in serverset_sd_configs")
 		}
 	}
 	for _, cfg := range c.StaticConfigs {
 		if cfg == nil {
-			return fmt.Errorf("empty or null section in static_configs")
+			return errors.New("empty or null section in static_configs")
 		}
 	}
 	return nil

discovery/consul/consul.go

@@ -25,10 +25,12 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	consul "github.com/hashicorp/consul/api"
-	"github.com/mwitkow/go-conntrack"
+	conntrack "github.com/mwitkow/go-conntrack"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/util/strutil"
 )
@@ -130,7 +132,7 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if strings.TrimSpace(c.Server) == "" {
-		return fmt.Errorf("consul SD configuration requires a server address")
+		return errors.New("consul SD configuration requires a server address")
 	}
 	return nil
 }
@@ -270,7 +272,7 @@ func (d *Discovery) getDatacenter() error {
 
 	dc, ok := info["Config"]["Datacenter"].(string)
 	if !ok {
-		err := fmt.Errorf("invalid value '%v' for Config.Datacenter", info["Config"]["Datacenter"])
+		err := errors.Errorf("invalid value '%v' for Config.Datacenter", info["Config"]["Datacenter"])
 		level.Error(d.logger).Log("msg", "Error retrieving datacenter name", "err", err)
 		return err
 	}

discovery/dns/dns.go

@@ -24,8 +24,10 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/miekg/dns"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/discovery/refresh"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 )
@@ -77,16 +79,16 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if len(c.Names) == 0 {
-		return fmt.Errorf("DNS-SD config must contain at least one SRV record name")
+		return errors.New("DNS-SD config must contain at least one SRV record name")
 	}
 	switch strings.ToUpper(c.Type) {
 	case "SRV":
 	case "A", "AAAA":
 		if c.Port == 0 {
-			return fmt.Errorf("a port is required in DNS-SD configs for all record types except SRV")
+			return errors.New("a port is required in DNS-SD configs for all record types except SRV")
 		}
 	default:
-		return fmt.Errorf("invalid DNS-SD records type %s", c.Type)
+		return errors.Errorf("invalid DNS-SD records type %s", c.Type)
 	}
 	return nil
 }
@@ -239,7 +241,7 @@ func (d *Discovery) refreshOne(ctx context.Context, name string, ch chan<- *targ
 func lookupWithSearchPath(name string, qtype uint16, logger log.Logger) (*dns.Msg, error) {
 	conf, err := dns.ClientConfigFromFile(resolvConf)
 	if err != nil {
-		return nil, fmt.Errorf("could not load resolv.conf: %s", err)
+		return nil, errors.Wrap(err, "could not load resolv.conf")
 	}
 
 	allResponsesValid := true
@@ -265,7 +267,7 @@ func lookupWithSearchPath(name string, qtype uint16, logger log.Logger) (*dns.Ms
 		return &dns.Msg{}, nil
 	}
 	// Outcome 3: boned.
-	return nil, fmt.Errorf("could not resolve %q: all servers responded with errors to at least one search domain", name)
+	return nil, errors.Errorf("could not resolve %q: all servers responded with errors to at least one search domain", name)
 }
 
 // lookupFromAnyServer uses all configured servers to try and resolve a specific
@@ -301,7 +303,7 @@ func lookupFromAnyServer(name string, qtype uint16, conf *dns.ClientConfig, logg
 		}
 	}
 
-	return nil, fmt.Errorf("could not resolve %s: no servers returned a viable answer", name)
+	return nil, errors.Errorf("could not resolve %s: no servers returned a viable answer", name)
 }
 
 // askServerForName makes a request to a specific DNS server for a specific
@@ -323,7 +325,7 @@ func askServerForName(name string, queryType uint16, client *dns.Client, servAdd
 
 	if response.Truncated {
 		if client.Net == "tcp" {
-			return nil, fmt.Errorf("got truncated message on TCP (64kiB limit exceeded?)")
+			return nil, errors.New("got truncated message on TCP (64kiB limit exceeded?)")
 		}
 
 		client.Net = "tcp"

discovery/ec2/ec2.go

@@ -25,11 +25,12 @@ import (
 	"github.com/aws/aws-sdk-go/aws/credentials/stscreds"
 	"github.com/aws/aws-sdk-go/aws/ec2metadata"
 	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/ec2"
 	"github.com/go-kit/kit/log"
+	"github.com/pkg/errors"
+	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 
-	"github.com/aws/aws-sdk-go/service/ec2"
-	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/prometheus/discovery/refresh"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/util/strutil"
@@ -95,13 +96,13 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		metadata := ec2metadata.New(sess)
 		region, err := metadata.Region()
 		if err != nil {
-			return fmt.Errorf("EC2 SD configuration requires a region")
+			return errors.New("EC2 SD configuration requires a region")
 		}
 		c.Region = region
 	}
 	for _, f := range c.Filters {
 		if len(f.Values) == 0 {
-			return fmt.Errorf("EC2 SD configuration filter values cannot be empty")
+			return errors.New("EC2 SD configuration filter values cannot be empty")
 		}
 	}
 	return nil
@@ -155,7 +156,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 		Profile: d.profile,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("could not create aws session: %s", err)
+		return nil, errors.Wrap(err, "could not create aws session")
 	}
 
 	var ec2s *ec2.EC2
@@ -247,7 +248,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 		}
 		return true
 	}); err != nil {
-		return nil, fmt.Errorf("could not describe instances: %s", err)
+		return nil, errors.Wrap(err, "could not describe instances")
 	}
 	return []*targetgroup.Group{tg}, nil
 }

discovery/file/file.go

@@ -16,7 +16,6 @@ package file
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -28,11 +27,13 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
+	fsnotify "gopkg.in/fsnotify/fsnotify.v1"
+	yaml "gopkg.in/yaml.v2"
+
 	"github.com/prometheus/prometheus/discovery/targetgroup"
-	"gopkg.in/fsnotify/fsnotify.v1"
-	"gopkg.in/yaml.v2"
 )
 
 var (
@@ -59,11 +60,11 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if len(c.Files) == 0 {
-		return fmt.Errorf("file service discovery config must contain at least one path name")
+		return errors.New("file service discovery config must contain at least one path name")
 	}
 	for _, name := range c.Files {
 		if !patFileSDName.MatchString(name) {
-			return fmt.Errorf("path name %q is not valid for file discovery", name)
+			return errors.Errorf("path name %q is not valid for file discovery", name)
 		}
 	}
 	return nil
@@ -382,7 +383,7 @@ func (d *Discovery) readFile(filename string) ([]*targetgroup.Group, error) {
 			return nil, err
 		}
 	default:
-		panic(fmt.Errorf("discovery.File.readFile: unhandled file extension %q", ext))
+		panic(errors.Errorf("discovery.File.readFile: unhandled file extension %q", ext))
 	}
 
 	for i, tg := range targetGroups {

discovery/gce/gce.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/go-kit/kit/log"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 	"golang.org/x/oauth2/google"
 	compute "google.golang.org/api/compute/v1"
@@ -83,10 +84,10 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if c.Project == "" {
-		return fmt.Errorf("GCE SD configuration requires a project")
+		return errors.New("GCE SD configuration requires a project")
 	}
 	if c.Zone == "" {
-		return fmt.Errorf("GCE SD configuration requires a zone")
+		return errors.New("GCE SD configuration requires a zone")
 	}
 	return nil
 }
@@ -117,11 +118,11 @@ func NewDiscovery(conf SDConfig, logger log.Logger) (*Discovery, error) {
 	var err error
 	d.client, err = google.DefaultClient(context.Background(), compute.ComputeReadonlyScope)
 	if err != nil {
-		return nil, fmt.Errorf("error setting up communication with GCE service: %s", err)
+		return nil, errors.Wrap(err, "error setting up communication with GCE service")
 	}
 	d.svc, err = compute.New(d.client)
 	if err != nil {
-		return nil, fmt.Errorf("error setting up communication with GCE service: %s", err)
+		return nil, errors.Wrap(err, "error setting up communication with GCE service")
 	}
 	d.isvc = compute.NewInstancesService(d.svc)
 
@@ -200,7 +201,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 		return nil
 	})
 	if err != nil {
-		return nil, fmt.Errorf("error retrieving refresh targets from gce: %s", err)
+		return nil, errors.Wrap(err, "error retrieving refresh targets from gce")
 	}
 	return []*targetgroup.Group{tg}, nil
 }

discovery/kubernetes/endpoints.go

@@ -15,17 +15,18 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 	"net"
 	"strconv"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/discovery/targetgroup"
 	apiv1 "k8s.io/api/core/v1"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/client-go/util/workqueue"
+
+	"github.com/prometheus/prometheus/discovery/targetgroup"
 )
 
 // Endpoints discovers new endpoint targets.
@@ -178,7 +179,7 @@ func convertToEndpoints(o interface{}) (*apiv1.Endpoints, error) {
 		return endpoints, nil
 	}
 
-	return nil, fmt.Errorf("received unexpected object: %v", o)
+	return nil, errors.Errorf("received unexpected object: %v", o)
 }
 
 func endpointsSource(ep *apiv1.Endpoints) string {

discovery/kubernetes/ingress.go

@@ -15,16 +15,17 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/discovery/targetgroup"
-	"github.com/prometheus/prometheus/util/strutil"
 	"k8s.io/api/extensions/v1beta1"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/client-go/util/workqueue"
+
+	"github.com/prometheus/prometheus/discovery/targetgroup"
+	"github.com/prometheus/prometheus/util/strutil"
 )
 
 // Ingress implements discovery of Kubernetes ingresss.
@@ -118,7 +119,7 @@ func convertToIngress(o interface{}) (*v1beta1.Ingress, error) {
 		return ingress, nil
 	}
 
-	return nil, fmt.Errorf("received unexpected object: %v", o)
+	return nil, errors.Errorf("received unexpected object: %v", o)
 }
 
 func ingressSource(s *v1beta1.Ingress) string {

discovery/kubernetes/kubernetes.go

@@ -15,13 +15,13 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 	"reflect"
 	"sync"
 	"time"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
@@ -80,7 +80,7 @@ func (c *Role) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	case RoleNode, RolePod, RoleService, RoleEndpoint, RoleIngress:
 		return nil
 	default:
-		return fmt.Errorf("unknown Kubernetes SD role %q", *c)
+		return errors.Errorf("unknown Kubernetes SD role %q", *c)
 	}
 }
 
@@ -101,14 +101,14 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if c.Role == "" {
-		return fmt.Errorf("role missing (one of: pod, service, endpoints, node, ingress)")
+		return errors.Errorf("role missing (one of: pod, service, endpoints, node, ingress)")
 	}
 	err = c.HTTPClientConfig.Validate()
 	if err != nil {
 		return err
 	}
 	if c.APIServer.URL == nil && !reflect.DeepEqual(c.HTTPClientConfig, config_util.HTTPClientConfig{}) {
-		return fmt.Errorf("to use custom HTTP client configuration please provide the 'api_server' URL explicitly")
+		return errors.Errorf("to use custom HTTP client configuration please provide the 'api_server' URL explicitly")
 	}
 	return nil
 }

discovery/kubernetes/node.go

@@ -15,18 +15,19 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 	"net"
 	"strconv"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/discovery/targetgroup"
-	"github.com/prometheus/prometheus/util/strutil"
 	apiv1 "k8s.io/api/core/v1"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/client-go/util/workqueue"
+
+	"github.com/prometheus/prometheus/discovery/targetgroup"
+	"github.com/prometheus/prometheus/util/strutil"
 )
 
 const (
@@ -127,7 +128,7 @@ func convertToNode(o interface{}) (*apiv1.Node, error) {
 		return node, nil
 	}
 
-	return nil, fmt.Errorf("received unexpected object: %v", o)
+	return nil, errors.Errorf("received unexpected object: %v", o)
 }
 
 func nodeSource(n *apiv1.Node) string {
@@ -214,5 +215,5 @@ func nodeAddress(node *apiv1.Node) (string, map[apiv1.NodeAddressType][]string,
 	if addresses, ok := m[apiv1.NodeHostName]; ok {
 		return addresses[0], m, nil
 	}
-	return "", m, fmt.Errorf("host address unknown")
+	return "", m, errors.New("host address unknown")
 }

discovery/kubernetes/pod.go

@@ -15,13 +15,13 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 	"net"
 	"strconv"
 	"strings"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 	apiv1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -131,7 +131,7 @@ func convertToPod(o interface{}) (*apiv1.Pod, error) {
 		return pod, nil
 	}
 
-	return nil, fmt.Errorf("received unexpected object: %v", o)
+	return nil, errors.Errorf("received unexpected object: %v", o)
 }
 
 const (

discovery/kubernetes/service.go

@@ -15,12 +15,12 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 	"net"
 	"strconv"
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 	apiv1 "k8s.io/api/core/v1"
 	"k8s.io/client-go/tools/cache"
@@ -123,7 +123,7 @@ func convertToService(o interface{}) (*apiv1.Service, error) {
 	if ok {
 		return service, nil
 	}
-	return nil, fmt.Errorf("received unexpected object: %v", o)
+	return nil, errors.Errorf("received unexpected object: %v", o)
 }
 
 func serviceSource(s *apiv1.Service) string {

discovery/marathon/marathon.go

@@ -26,6 +26,7 @@ import (
 	"time"
 
 	"github.com/go-kit/kit/log"
+	"github.com/pkg/errors"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 
@@ -79,16 +80,16 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if len(c.Servers) == 0 {
-		return fmt.Errorf("marathon_sd: must contain at least one Marathon server")
+		return errors.New("marathon_sd: must contain at least one Marathon server")
 	}
 	if len(c.AuthToken) > 0 && len(c.AuthTokenFile) > 0 {
-		return fmt.Errorf("marathon_sd: at most one of auth_token & auth_token_file must be configured")
+		return errors.New("marathon_sd: at most one of auth_token & auth_token_file must be configured")
 	}
 	if c.HTTPClientConfig.BasicAuth != nil && (len(c.AuthToken) > 0 || len(c.AuthTokenFile) > 0) {
-		return fmt.Errorf("marathon_sd: at most one of basic_auth, auth_token & auth_token_file must be configured")
+		return errors.New("marathon_sd: at most one of basic_auth, auth_token & auth_token_file must be configured")
 	}
 	if (len(c.HTTPClientConfig.BearerToken) > 0 || len(c.HTTPClientConfig.BearerTokenFile) > 0) && (len(c.AuthToken) > 0 || len(c.AuthTokenFile) > 0) {
-		return fmt.Errorf("marathon_sd: at most one of bearer_token, bearer_token_file, auth_token & auth_token_file must be configured")
+		return errors.New("marathon_sd: at most one of bearer_token, bearer_token_file, auth_token & auth_token_file must be configured")
 	}
 	return c.HTTPClientConfig.Validate()
 }
@@ -163,7 +164,7 @@ func newAuthTokenFileRoundTripper(tokenFile string, rt http.RoundTripper) (http.
 	// fail-fast if we can't read the file.
 	_, err := ioutil.ReadFile(tokenFile)
 	if err != nil {
-		return nil, fmt.Errorf("unable to read auth token file %s: %s", tokenFile, err)
+		return nil, errors.Wrapf(err, "unable to read auth token file %s", tokenFile)
 	}
 	return &authTokenFileRoundTripper{tokenFile, rt}, nil
 }
@@ -171,7 +172,7 @@ func newAuthTokenFileRoundTripper(tokenFile string, rt http.RoundTripper) (http.
 func (rt *authTokenFileRoundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
 	b, err := ioutil.ReadFile(rt.authTokenFile)
 	if err != nil {
-		return nil, fmt.Errorf("unable to read auth token file %s: %s", rt.authTokenFile, err)
+		return nil, errors.Wrapf(err, "unable to read auth token file %s", rt.authTokenFile)
 	}
 	authToken := strings.TrimSpace(string(b))
 
@@ -308,13 +309,13 @@ func fetchApps(ctx context.Context, client *http.Client, url string) (*appList,
 	defer resp.Body.Close()
 
 	if (resp.StatusCode < 200) || (resp.StatusCode >= 300) {
-		return nil, fmt.Errorf("non 2xx status '%v' response during marathon service discovery", resp.StatusCode)
+		return nil, errors.Errorf("non 2xx status '%v' response during marathon service discovery", resp.StatusCode)
 	}
 
 	var apps appList
 	err = json.NewDecoder(resp.Body).Decode(&apps)
 	if err != nil {
-		return nil, fmt.Errorf("%q: %v", url, err)
+		return nil, errors.Wrapf(err, "%q", url)
 	}
 	return &apps, nil
 }

discovery/openstack/hypervisor.go

@@ -23,7 +23,9 @@ import (
 	"github.com/gophercloud/gophercloud/openstack"
 	"github.com/gophercloud/gophercloud/openstack/compute/v2/extensions/hypervisors"
 	"github.com/gophercloud/gophercloud/pagination"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 )
 
@@ -55,13 +57,13 @@ func (h *HypervisorDiscovery) refresh(ctx context.Context) ([]*targetgroup.Group
 	h.provider.Context = ctx
 	err := openstack.Authenticate(h.provider, *h.authOpts)
 	if err != nil {
-		return nil, fmt.Errorf("could not authenticate to OpenStack: %s", err)
+		return nil, errors.Wrap(err, "could not authenticate to OpenStack")
 	}
 	client, err := openstack.NewComputeV2(h.provider, gophercloud.EndpointOpts{
 		Region: h.region,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("could not create OpenStack compute session: %s", err)
+		return nil, errors.Wrap(err, "could not create OpenStack compute session")
 	}
 
 	tg := &targetgroup.Group{
@@ -73,7 +75,7 @@ func (h *HypervisorDiscovery) refresh(ctx context.Context) ([]*targetgroup.Group
 	err = pagerHypervisors.EachPage(func(page pagination.Page) (bool, error) {
 		hypervisorList, err := hypervisors.ExtractHypervisors(page)
 		if err != nil {
-			return false, fmt.Errorf("could not extract hypervisors: %s", err)
+			return false, errors.Wrap(err, "could not extract hypervisors")
 		}
 		for _, hypervisor := range hypervisorList {
 			labels := model.LabelSet{}

discovery/openstack/instance.go

@@ -25,6 +25,7 @@ import (
 	"github.com/gophercloud/gophercloud/openstack/compute/v2/extensions/floatingips"
 	"github.com/gophercloud/gophercloud/openstack/compute/v2/servers"
 	"github.com/gophercloud/gophercloud/pagination"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/discovery/targetgroup"
@@ -72,13 +73,13 @@ func (i *InstanceDiscovery) refresh(ctx context.Context) ([]*targetgroup.Group,
 	i.provider.Context = ctx
 	err := openstack.Authenticate(i.provider, *i.authOpts)
 	if err != nil {
-		return nil, fmt.Errorf("could not authenticate to OpenStack: %s", err)
+		return nil, errors.Wrap(err, "could not authenticate to OpenStack")
 	}
 	client, err := openstack.NewComputeV2(i.provider, gophercloud.EndpointOpts{
 		Region: i.region,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("could not create OpenStack compute session: %s", err)
+		return nil, errors.Wrap(err, "could not create OpenStack compute session")
 	}
 
 	// OpenStack API reference
@@ -89,7 +90,7 @@ func (i *InstanceDiscovery) refresh(ctx context.Context) ([]*targetgroup.Group,
 	err = pagerFIP.EachPage(func(page pagination.Page) (bool, error) {
 		result, err := floatingips.ExtractFloatingIPs(page)
 		if err != nil {
-			return false, fmt.Errorf("could not extract floatingips: %s", err)
+			return false, errors.Wrap(err, "could not extract floatingips")
 		}
 		for _, ip := range result {
 			// Skip not associated ips
@@ -116,11 +117,11 @@ func (i *InstanceDiscovery) refresh(ctx context.Context) ([]*targetgroup.Group,
 	}
 	err = pager.EachPage(func(page pagination.Page) (bool, error) {
 		if ctx.Err() != nil {
-			return false, fmt.Errorf("could not extract instances: %s", ctx.Err())
+			return false, errors.Wrap(ctx.Err(), "could not extract instances")
 		}
 		instanceList, err := servers.ExtractServers(page)
 		if err != nil {
-			return false, fmt.Errorf("could not extract instances: %s", err)
+			return false, errors.Wrap(err, "could not extract instances")
 		}
 
 		for _, s := range instanceList {

discovery/openstack/openstack.go

@@ -15,15 +15,14 @@ package openstack
 
 import (
 	"context"
-	"errors"
-	"fmt"
 	"net/http"
 	"time"
 
 	"github.com/go-kit/kit/log"
 	"github.com/gophercloud/gophercloud"
 	"github.com/gophercloud/gophercloud/openstack"
-	"github.com/mwitkow/go-conntrack"
+	conntrack "github.com/mwitkow/go-conntrack"
+	"github.com/pkg/errors"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 
@@ -80,7 +79,7 @@ func (c *Role) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	case OpenStackRoleHypervisor, OpenStackRoleInstance:
 		return nil
 	default:
-		return fmt.Errorf("unknown OpenStack SD role %q", *c)
+		return errors.Errorf("unknown OpenStack SD role %q", *c)
 	}
 }
 
@@ -93,10 +92,10 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if c.Role == "" {
-		return fmt.Errorf("role missing (one of: instance, hypervisor)")
+		return errors.New("role missing (one of: instance, hypervisor)")
 	}
 	if c.Region == "" {
-		return fmt.Errorf("openstack SD configuration requires a region")
+		return errors.New("openstack SD configuration requires a region")
 	}
 	return nil
 }

discovery/triton/triton.go

@@ -24,7 +24,8 @@ import (
 	"time"
 
 	"github.com/go-kit/kit/log"
-	"github.com/mwitkow/go-conntrack"
+	conntrack "github.com/mwitkow/go-conntrack"
+	"github.com/pkg/errors"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 
@@ -70,16 +71,16 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if c.Account == "" {
-		return fmt.Errorf("triton SD configuration requires an account")
+		return errors.New("triton SD configuration requires an account")
 	}
 	if c.DNSSuffix == "" {
-		return fmt.Errorf("triton SD configuration requires a dns_suffix")
+		return errors.New("triton SD configuration requires a dns_suffix")
 	}
 	if c.Endpoint == "" {
-		return fmt.Errorf("triton SD configuration requires an endpoint")
+		return errors.New("triton SD configuration requires an endpoint")
 	}
 	if c.RefreshInterval <= 0 {
-		return fmt.Errorf("triton SD configuration requires RefreshInterval to be a positive integer")
+		return errors.New("triton SD configuration requires RefreshInterval to be a positive integer")
 	}
 	return nil
 }
@@ -153,20 +154,20 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 	req = req.WithContext(ctx)
 	resp, err := d.client.Do(req)
 	if err != nil {
-		return nil, fmt.Errorf("an error occurred when requesting targets from the discovery endpoint: %s", err)
+		return nil, errors.Wrap(err, "an error occurred when requesting targets from the discovery endpoint")
 	}
 
 	defer resp.Body.Close()
 
 	data, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
-		return nil, fmt.Errorf("an error occurred when reading the response body: %s", err)
+		return nil, errors.Wrap(err, "an error occurred when reading the response body")
 	}
 
 	dr := discoveryResponse{}
 	err = json.Unmarshal(data, &dr)
 	if err != nil {
-		return nil, fmt.Errorf("an error occurred unmarshaling the discovery response json: %s", err)
+		return nil, errors.Wrap(err, "an error occurred unmarshaling the discovery response json")
 	}
 
 	for _, container := range dr.Containers {

discovery/zookeeper/zookeeper.go

@@ -23,6 +23,7 @@ import (
 	"time"
 
 	"github.com/go-kit/kit/log"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 	"github.com/samuel/go-zookeeper/zk"
 
@@ -58,14 +59,14 @@ func (c *ServersetSDConfig) UnmarshalYAML(unmarshal func(interface{}) error) err
 		return err
 	}
 	if len(c.Servers) == 0 {
-		return fmt.Errorf("serverset SD config must contain at least one Zookeeper server")
+		return errors.New("serverset SD config must contain at least one Zookeeper server")
 	}
 	if len(c.Paths) == 0 {
-		return fmt.Errorf("serverset SD config must contain at least one path")
+		return errors.New("serverset SD config must contain at least one path")
 	}
 	for _, path := range c.Paths {
 		if !strings.HasPrefix(path, "/") {
-			return fmt.Errorf("serverset SD config paths must begin with '/': %s", path)
+			return errors.Errorf("serverset SD config paths must begin with '/': %s", path)
 		}
 	}
 	return nil
@@ -87,14 +88,14 @@ func (c *NerveSDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		return err
 	}
 	if len(c.Servers) == 0 {
-		return fmt.Errorf("nerve SD config must contain at least one Zookeeper server")
+		return errors.New("nerve SD config must contain at least one Zookeeper server")
 	}
 	if len(c.Paths) == 0 {
-		return fmt.Errorf("nerve SD config must contain at least one path")
+		return errors.New("nerve SD config must contain at least one path")
 	}
 	for _, path := range c.Paths {
 		if !strings.HasPrefix(path, "/") {
-			return fmt.Errorf("nerve SD config paths must begin with '/': %s", path)
+			return errors.Errorf("nerve SD config paths must begin with '/': %s", path)
 		}
 	}
 	return nil
@@ -223,7 +224,7 @@ func parseServersetMember(data []byte, path string) (model.LabelSet, error) {
 	member := serversetMember{}
 
 	if err := json.Unmarshal(data, &member); err != nil {
-		return nil, fmt.Errorf("error unmarshaling serverset member %q: %s", path, err)
+		return nil, errors.Wrapf(err, "error unmarshaling serverset member %q", path)
 	}
 
 	labels := model.LabelSet{}
@@ -265,7 +266,7 @@ func parseNerveMember(data []byte, path string) (model.LabelSet, error) {
 	member := nerveMember{}
 	err := json.Unmarshal(data, &member)
 	if err != nil {
-		return nil, fmt.Errorf("error unmarshaling nerve member %q: %s", path, err)
+		return nil, errors.Wrapf(err, "error unmarshaling nerve member %q", path)
 	}
 
 	labels := model.LabelSet{}

documentation/examples/remote_storage/remote_storage_adapter/influxdb/client.go

@@ -22,11 +22,12 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	influx "github.com/influxdata/influxdb/client/v2"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/prompb"
 
-	influx "github.com/influxdata/influxdb/client/v2"
+	"github.com/prometheus/prometheus/prompb"
 )
 
 // Client allows sending batches of Prometheus samples to InfluxDB.
@@ -125,7 +126,7 @@ func (c *Client) Read(req *prompb.ReadRequest) (*prompb.ReadResponse, error) {
 			return nil, err
 		}
 		if resp.Err != "" {
-			return nil, fmt.Errorf(resp.Err)
+			return nil, errors.New(resp.Err)
 		}
 
 		if err = mergeResult(labelsToSeries, resp.Results); err != nil {
@@ -158,7 +159,7 @@ func (c *Client) buildCommand(q *prompb.Query) (string, error) {
 				from = fmt.Sprintf("FROM %q./^%s$/", c.retentionPolicy, escapeSlashes(m.Value))
 			default:
 				// TODO: Figure out how to support these efficiently.
-				return "", fmt.Errorf("non-equal or regex-non-equal matchers are not supported on the metric name yet")
+				return "", errors.New("non-equal or regex-non-equal matchers are not supported on the metric name yet")
 			}
 			continue
 		}
@@ -173,7 +174,7 @@ func (c *Client) buildCommand(q *prompb.Query) (string, error) {
 		case prompb.LabelMatcher_NRE:
 			matchers = append(matchers, fmt.Sprintf("%q !~ /^%s$/", m.Name, escapeSlashes(m.Value)))
 		default:
-			return "", fmt.Errorf("unknown match type %v", m.Type)
+			return "", errors.Errorf("unknown match type %v", m.Type)
 		}
 	}
 	matchers = append(matchers, fmt.Sprintf("time >= %vms", q.StartTimestampMs))
@@ -252,27 +253,27 @@ func valuesToSamples(values [][]interface{}) ([]prompb.Sample, error) {
 	samples := make([]prompb.Sample, 0, len(values))
 	for _, v := range values {
 		if len(v) != 2 {
-			return nil, fmt.Errorf("bad sample tuple length, expected [<timestamp>, <value>], got %v", v)
+			return nil, errors.Errorf("bad sample tuple length, expected [<timestamp>, <value>], got %v", v)
 		}
 
 		jsonTimestamp, ok := v[0].(json.Number)
 		if !ok {
-			return nil, fmt.Errorf("bad timestamp: %v", v[0])
+			return nil, errors.Errorf("bad timestamp: %v", v[0])
 		}
 
 		jsonValue, ok := v[1].(json.Number)
 		if !ok {
-			return nil, fmt.Errorf("bad sample value: %v", v[1])
+			return nil, errors.Errorf("bad sample value: %v", v[1])
 		}
 
 		timestamp, err := jsonTimestamp.Int64()
 		if err != nil {
-			return nil, fmt.Errorf("unable to convert sample timestamp to int64: %v", err)
+			return nil, errors.Wrap(err, "unable to convert sample timestamp to int64")
 		}
 
 		value, err := jsonValue.Float64()
 		if err != nil {
-			return nil, fmt.Errorf("unable to convert sample value to float64: %v", err)
+			return nil, errors.Wrap(err, "unable to convert sample value to float64")
 		}
 
 		samples = append(samples, prompb.Sample{

documentation/examples/remote_storage/remote_storage_adapter/opentsdb/client.go

@@ -17,7 +17,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"math"
 	"net/http"
@@ -26,6 +25,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 )
 
@@ -133,7 +133,7 @@ func (c *Client) Write(samples model.Samples) error {
 	if err := json.Unmarshal(buf, &r); err != nil {
 		return err
 	}
-	return fmt.Errorf("failed to write %d samples to OpenTSDB, %d succeeded", r["failed"], r["success"])
+	return errors.Errorf("failed to write %d samples to OpenTSDB, %d succeeded", r["failed"], r["success"])
 }
 
 // Name identifies the client as an OpenTSDB client.

documentation/examples/remote_storage/remote_storage_adapter/opentsdb/tagvalue.go

@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"fmt"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 )
 
@@ -97,13 +98,13 @@ func (tv *TagValue) UnmarshalJSON(json []byte) error {
 	for i, b := range json {
 		if i == 0 {
 			if b != '"' {
-				return fmt.Errorf("expected '\"', got %q", b)
+				return errors.Errorf("expected '\"', got %q", b)
 			}
 			continue
 		}
 		if i == len(json)-1 {
 			if b != '"' {
-				return fmt.Errorf("expected '\"', got %q", b)
+				return errors.Errorf("expected '\"', got %q", b)
 			}
 			break
 		}
@@ -129,7 +130,7 @@ func (tv *TagValue) UnmarshalJSON(json []byte) error {
 				parsedByte = (b - 55) << 4
 				escapeLevel = 2
 			default:
-				return fmt.Errorf(
+				return errors.Errorf(
 					"illegal escape sequence at byte %d (%c)",
 					i, b,
 				)
@@ -141,7 +142,7 @@ func (tv *TagValue) UnmarshalJSON(json []byte) error {
 			case b >= 'A' && b <= 'F': // A-F
 				parsedByte += b - 55
 			default:
-				return fmt.Errorf(
+				return errors.Errorf(
 					"illegal escape sequence at byte %d (%c)",
 					i, b,
 				)

notifier/notifier.go

@@ -30,6 +30,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
@@ -511,7 +512,7 @@ func (n *Manager) sendOne(ctx context.Context, c *http.Client, url string, b []b
 
 	// Any HTTP status 2xx is OK.
 	if resp.StatusCode/100 != 2 {
-		return fmt.Errorf("bad response status %v", resp.Status)
+		return errors.Errorf("bad response status %s", resp.Status)
 	}
 	return err
 }
@@ -662,7 +663,7 @@ func alertmanagerFromGroup(tg *targetgroup.Group, cfg *config.AlertmanagerConfig
 			case "https":
 				addr = addr + ":443"
 			default:
-				return nil, nil, fmt.Errorf("invalid scheme: %q", cfg.Scheme)
+				return nil, nil, errors.Errorf("invalid scheme: %q", cfg.Scheme)
 			}
 			lb.Set(model.AddressLabel, addr)
 		}

pkg/relabel/relabel.go

@@ -19,6 +19,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/pkg/labels"
@@ -66,7 +67,7 @@ func (a *Action) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		*a = act
 		return nil
 	}
-	return fmt.Errorf("unknown relabel action %q", s)
+	return errors.Errorf("unknown relabel action %q", s)
 }
 
 // Config is the configuration for relabeling of target label sets.
@@ -100,19 +101,19 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		c.Regex = MustNewRegexp("")
 	}
 	if c.Modulus == 0 && c.Action == HashMod {
-		return fmt.Errorf("relabel configuration for hashmod requires non-zero modulus")
+		return errors.Errorf("relabel configuration for hashmod requires non-zero modulus")
 	}
 	if (c.Action == Replace || c.Action == HashMod) && c.TargetLabel == "" {
-		return fmt.Errorf("relabel configuration for %s action requires 'target_label' value", c.Action)
+		return errors.Errorf("relabel configuration for %s action requires 'target_label' value", c.Action)
 	}
 	if c.Action == Replace && !relabelTarget.MatchString(c.TargetLabel) {
-		return fmt.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
+		return errors.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
 	}
 	if c.Action == LabelMap && !relabelTarget.MatchString(c.Replacement) {
-		return fmt.Errorf("%q is invalid 'replacement' for %s action", c.Replacement, c.Action)
+		return errors.Errorf("%q is invalid 'replacement' for %s action", c.Replacement, c.Action)
 	}
 	if c.Action == HashMod && !model.LabelName(c.TargetLabel).IsValid() {
-		return fmt.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
+		return errors.Errorf("%q is invalid 'target_label' for %s action", c.TargetLabel, c.Action)
 	}
 
 	if c.Action == LabelDrop || c.Action == LabelKeep {
@@ -121,7 +122,7 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 			c.Modulus != DefaultRelabelConfig.Modulus ||
 			c.Separator != DefaultRelabelConfig.Separator ||
 			c.Replacement != DefaultRelabelConfig.Replacement {
-			return fmt.Errorf("%s action requires only 'regex', and no other fields", c.Action)
+			return errors.Errorf("%s action requires only 'regex', and no other fields", c.Action)
 		}
 	}
 
@@ -247,7 +248,7 @@ func relabel(lset labels.Labels, cfg *Config) labels.Labels {
 			}
 		}
 	default:
-		panic(fmt.Errorf("relabel: unknown relabel action type %q", cfg.Action))
+		panic(errors.Errorf("relabel: unknown relabel action type %q", cfg.Action))
 	}
 
 	return lb.Labels()

pkg/rulefmt/rulefmt.go

@@ -15,16 +15,16 @@ package rulefmt
 
 import (
 	"context"
-	"fmt"
 	"io/ioutil"
 	"time"
 
 	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+	yaml "gopkg.in/yaml.v2"
+
 	"github.com/prometheus/prometheus/pkg/timestamp"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/template"
-	"gopkg.in/yaml.v2"
 )
 
 // Error represents semantical errors on parsing rule groups.
@@ -174,7 +174,7 @@ func testTemplateParsing(rl *Rule) (errs []error) {
 	for _, val := range rl.Labels {
 		err := parseTest(val)
 		if err != nil {
-			errs = append(errs, fmt.Errorf("msg=%s", err.Error()))
+			errs = append(errs, errors.Errorf("msg=%s", err.Error()))
 		}
 	}
 
@@ -182,7 +182,7 @@ func testTemplateParsing(rl *Rule) (errs []error) {
 	for _, val := range rl.Annotations {
 		err := parseTest(val)
 		if err != nil {
-			errs = append(errs, fmt.Errorf("msg=%s", err.Error()))
+			errs = append(errs, errors.Errorf("msg=%s", err.Error()))
 		}
 	}
 

pkg/textparse/openmetricslex.l.go

@@ -16,7 +16,7 @@
 package textparse
 
 import (
-	"fmt"
+	"github.com/pkg/errors"
 )
 
 // Lex is called by the parser generated by "go tool yacc" to obtain each
@@ -33,7 +33,7 @@ yystate0:
 
 	switch yyt := l.state; yyt {
 	default:
-		panic(fmt.Errorf(`invalid start condition %d`, yyt))
+		panic(errors.Errorf(`invalid start condition %d`, yyt))
 	case 0: // start condition: INITIAL
 		goto yystart1
 	case 1: // start condition: sComment

pkg/textparse/openmetricsparse.go

@@ -17,8 +17,6 @@
 package textparse
 
 import (
-	"errors"
-	"fmt"
 	"io"
 	"math"
 	"sort"
@@ -26,6 +24,8 @@ import (
 	"strings"
 	"unicode/utf8"
 
+	"github.com/pkg/errors"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/value"
 )
@@ -185,7 +185,7 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 	switch t := p.nextToken(); t {
 	case tEofWord:
 		if t := p.nextToken(); t != tEOF {
-			return EntryInvalid, fmt.Errorf("unexpected data after # EOF")
+			return EntryInvalid, errors.New("unexpected data after # EOF")
 		}
 		return EntryInvalid, io.EOF
 	case tEOF:
@@ -227,11 +227,11 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 			case "unknown":
 				p.mtype = MetricTypeUnknown
 			default:
-				return EntryInvalid, fmt.Errorf("invalid metric type %q", s)
+				return EntryInvalid, errors.Errorf("invalid metric type %q", s)
 			}
 		case tHelp:
 			if !utf8.Valid(p.text) {
-				return EntryInvalid, fmt.Errorf("help text is not a valid utf8 string")
+				return EntryInvalid, errors.New("help text is not a valid utf8 string")
 			}
 		}
 		switch t {
@@ -244,7 +244,7 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 			u := yoloString(p.text)
 			if len(u) > 0 {
 				if !strings.HasSuffix(m, u) || len(m) < len(u)+1 || p.l.b[p.offsets[1]-len(u)-1] != '_' {
-					return EntryInvalid, fmt.Errorf("unit not a suffix of metric %q", m)
+					return EntryInvalid, errors.Errorf("unit not a suffix of metric %q", m)
 				}
 			}
 			return EntryUnit, nil
@@ -293,7 +293,7 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 		return EntrySeries, nil
 
 	default:
-		err = fmt.Errorf("%q %q is not a valid start token", t, string(p.l.cur()))
+		err = errors.Errorf("%q %q is not a valid start token", t, string(p.l.cur()))
 	}
 	return EntryInvalid, err
 }
@@ -336,7 +336,7 @@ func (p *OpenMetricsParser) parseLVals() error {
 			return parseError("expected label value", t)
 		}
 		if !utf8.Valid(p.l.buf()) {
-			return fmt.Errorf("invalid UTF-8 label value")
+			return errors.New("invalid UTF-8 label value")
 		}
 
 		// The openMetricsLexer ensures the value string is quoted. Strip first

pkg/textparse/promlex.l.go

@@ -16,7 +16,7 @@
 package textparse
 
 import (
-	"fmt"
+	"github.com/pkg/errors"
 )
 
 const (
@@ -44,7 +44,7 @@ yystate0:
 
 	switch yyt := l.state; yyt {
 	default:
-		panic(fmt.Errorf(`invalid start condition %d`, yyt))
+		panic(errors.Errorf(`invalid start condition %d`, yyt))
 	case 0: // start condition: INITIAL
 		goto yystart1
 	case 1: // start condition: sComment

pkg/textparse/promparse.go

@@ -17,7 +17,6 @@
 package textparse
 
 import (
-	"errors"
 	"fmt"
 	"io"
 	"math"
@@ -27,6 +26,8 @@ import (
 	"unicode/utf8"
 	"unsafe"
 
+	"github.com/pkg/errors"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/value"
 )
@@ -244,7 +245,7 @@ func (p *PromParser) nextToken() token {
 }
 
 func parseError(exp string, got token) error {
-	return fmt.Errorf("%s, got %q", exp, got)
+	return errors.Errorf("%s, got %q", exp, got)
 }
 
 // Next advances the parser to the next sample. It returns false if no
@@ -293,11 +294,11 @@ func (p *PromParser) Next() (Entry, error) {
 			case "untyped":
 				p.mtype = MetricTypeUnknown
 			default:
-				return EntryInvalid, fmt.Errorf("invalid metric type %q", s)
+				return EntryInvalid, errors.Errorf("invalid metric type %q", s)
 			}
 		case tHelp:
 			if !utf8.Valid(p.text) {
-				return EntryInvalid, fmt.Errorf("help text is not a valid utf8 string")
+				return EntryInvalid, errors.Errorf("help text is not a valid utf8 string")
 			}
 		}
 		if t := p.nextToken(); t != tLinebreak {
@@ -356,7 +357,7 @@ func (p *PromParser) Next() (Entry, error) {
 		return EntrySeries, nil
 
 	default:
-		err = fmt.Errorf("%q is not a valid start token", t)
+		err = errors.Errorf("%q is not a valid start token", t)
 	}
 	return EntryInvalid, err
 }
@@ -380,7 +381,7 @@ func (p *PromParser) parseLVals() error {
 			return parseError("expected label value", t)
 		}
 		if !utf8.Valid(p.l.buf()) {
-			return fmt.Errorf("invalid UTF-8 label value")
+			return errors.Errorf("invalid UTF-8 label value")
 		}
 
 		// The promlexer ensures the value string is quoted. Strip first

promql/ast.go

@@ -14,9 +14,10 @@
 package promql
 
 import (
-	"fmt"
 	"time"
 
+	"github.com/pkg/errors"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/storage"
 )
@@ -301,7 +302,7 @@ func Walk(v Visitor, node Node, path []Node) error {
 		// nothing to do
 
 	default:
-		panic(fmt.Errorf("promql.Walk: unhandled node type %T", node))
+		panic(errors.Errorf("promql.Walk: unhandled node type %T", node))
 	}
 
 	_, err = v.Visit(nil, nil)

promql/engine.go

@@ -29,8 +29,10 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/pkg/gate"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/timestamp"
@@ -307,7 +309,7 @@ func (ng *Engine) NewRangeQuery(q storage.Queryable, qs string, start, end time.
 		return nil, err
 	}
 	if expr.Type() != ValueTypeVector && expr.Type() != ValueTypeScalar {
-		return nil, fmt.Errorf("invalid expression type %q for range query, must be Scalar or instant Vector", documentedType(expr.Type()))
+		return nil, errors.Errorf("invalid expression type %q for range query, must be Scalar or instant Vector", documentedType(expr.Type()))
 	}
 	qry := ng.newQuery(q, expr, start, end, interval)
 	qry.q = qs
@@ -391,7 +393,7 @@ func (ng *Engine) exec(ctx context.Context, q *query) (Value, storage.Warnings,
 		return nil, nil, s(ctx)
 	}
 
-	panic(fmt.Errorf("promql.Engine.exec: unhandled statement of type %T", q.Statement()))
+	panic(errors.Errorf("promql.Engine.exec: unhandled statement of type %T", q.Statement()))
 }
 
 func timeMilliseconds(t time.Time) int64 {
@@ -441,7 +443,7 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *EvalStmt) (
 
 		mat, ok := val.(Matrix)
 		if !ok {
-			panic(fmt.Errorf("promql.Engine.exec: invalid expression type %q", val.Type()))
+			panic(errors.Errorf("promql.Engine.exec: invalid expression type %q", val.Type()))
 		}
 		query.matrix = mat
 		switch s.Expr.Type() {
@@ -459,7 +461,7 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *EvalStmt) (
 		case ValueTypeMatrix:
 			return mat, warnings, nil
 		default:
-			panic(fmt.Errorf("promql.Engine.exec: unexpected expression type %q", s.Expr.Type()))
+			panic(errors.Errorf("promql.Engine.exec: unexpected expression type %q", s.Expr.Type()))
 		}
 
 	}
@@ -482,7 +484,7 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *EvalStmt) (
 
 	mat, ok := val.(Matrix)
 	if !ok {
-		panic(fmt.Errorf("promql.Engine.exec: invalid expression type %q", val.Type()))
+		panic(errors.Errorf("promql.Engine.exec: invalid expression type %q", val.Type()))
 	}
 	query.matrix = mat
 
@@ -666,7 +668,7 @@ type evaluator struct {
 
 // errorf causes a panic with the input formatted into an error.
 func (ev *evaluator) errorf(format string, args ...interface{}) {
-	ev.error(fmt.Errorf(format, args...))
+	ev.error(errors.Errorf(format, args...))
 }
 
 // error causes a panic with the given error.
@@ -686,7 +688,7 @@ func (ev *evaluator) recover(errp *error) {
 		buf = buf[:runtime.Stack(buf, false)]
 
 		level.Error(ev.logger).Log("msg", "runtime panic in parser", "err", e, "stacktrace", string(buf))
-		*errp = fmt.Errorf("unexpected error: %s", err)
+		*errp = errors.Wrap(err, "unexpected error")
 	} else {
 		*errp = e.(error)
 	}
@@ -1127,7 +1129,7 @@ func (ev *evaluator) eval(expr Expr) Value {
 
 	case *MatrixSelector:
 		if ev.startTimestamp != ev.endTimestamp {
-			panic(fmt.Errorf("cannot do range evaluation of matrix selector"))
+			panic(errors.New("cannot do range evaluation of matrix selector"))
 		}
 		return ev.matrixSelector(e)
 
@@ -1160,7 +1162,7 @@ func (ev *evaluator) eval(expr Expr) Value {
 		return res
 	}
 
-	panic(fmt.Errorf("unhandled expression of type: %T", expr))
+	panic(errors.Errorf("unhandled expression of type: %T", expr))
 }
 
 func durationToInt64Millis(d time.Duration) int64 {
@@ -1629,7 +1631,7 @@ func scalarBinop(op ItemType, lhs, rhs float64) float64 {
 	case ItemLTE:
 		return btos(lhs <= rhs)
 	}
-	panic(fmt.Errorf("operator %q not allowed for Scalar operations", op))
+	panic(errors.Errorf("operator %q not allowed for Scalar operations", op))
 }
 
 // vectorElemBinop evaluates a binary operation between two Vector elements.
@@ -1660,7 +1662,7 @@ func vectorElemBinop(op ItemType, lhs, rhs float64) (float64, bool) {
 	case ItemLTE:
 		return lhs, lhs <= rhs
 	}
-	panic(fmt.Errorf("operator %q not allowed for operations between Vectors", op))
+	panic(errors.Errorf("operator %q not allowed for operations between Vectors", op))
 }
 
 type groupedAggregation struct {
@@ -1824,7 +1826,7 @@ func (ev *evaluator) aggregation(op ItemType, grouping []string, without bool, p
 			group.heap = append(group.heap, s)
 
 		default:
-			panic(fmt.Errorf("expected aggregation operator but got %q", op))
+			panic(errors.Errorf("expected aggregation operator but got %q", op))
 		}
 	}
 

promql/engine_test.go

@@ -15,12 +15,13 @@ package promql
 
 import (
 	"context"
-	"fmt"
 	"reflect"
 	"testing"
 	"time"
 
 	"github.com/go-kit/kit/log"
+	"github.com/pkg/errors"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/util/testutil"
@@ -194,7 +195,7 @@ func TestQueryError(t *testing.T) {
 		Timeout:       10 * time.Second,
 	}
 	engine := NewEngine(opts)
-	errStorage := ErrStorage{fmt.Errorf("storage error")}
+	errStorage := ErrStorage{errors.New("storage error")}
 	queryable := storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
 		return &errQuerier{err: errStorage}, nil
 	})
@@ -641,7 +642,7 @@ func TestRecoverEvaluatorError(t *testing.T) {
 	ev := &evaluator{logger: log.NewNopLogger()}
 	var err error
 
-	e := fmt.Errorf("custom error")
+	e := errors.New("custom error")
 
 	defer func() {
 		if err.Error() != e.Error() {

promql/functions.go

@@ -14,7 +14,6 @@
 package promql
 
 import (
-	"fmt"
 	"math"
 	"regexp"
 	"sort"
@@ -22,7 +21,9 @@ import (
 	"strings"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 )
 
@@ -232,10 +233,10 @@ func funcHoltWinters(vals []Value, args Expressions, enh *EvalNodeHelper) Vector
 
 	// Sanity check the input.
 	if sf <= 0 || sf >= 1 {
-		panic(fmt.Errorf("invalid smoothing factor. Expected: 0 < sf < 1, got: %f", sf))
+		panic(errors.Errorf("invalid smoothing factor. Expected: 0 < sf < 1, got: %f", sf))
 	}
 	if tf <= 0 || tf >= 1 {
-		panic(fmt.Errorf("invalid trend factor. Expected: 0 < tf < 1, got: %f", tf))
+		panic(errors.Errorf("invalid trend factor. Expected: 0 < tf < 1, got: %f", tf))
 	}
 
 	var l int
@@ -730,10 +731,10 @@ func funcLabelReplace(vals []Value, args Expressions, enh *EvalNodeHelper) Vecto
 		var err error
 		enh.regex, err = regexp.Compile("^(?:" + regexStr + ")$")
 		if err != nil {
-			panic(fmt.Errorf("invalid regular expression in label_replace(): %s", regexStr))
+			panic(errors.Errorf("invalid regular expression in label_replace(): %s", regexStr))
 		}
 		if !model.LabelNameRE.MatchString(dst) {
-			panic(fmt.Errorf("invalid destination label name in label_replace(): %s", dst))
+			panic(errors.Errorf("invalid destination label name in label_replace(): %s", dst))
 		}
 		enh.dmn = make(map[uint64]labels.Labels, len(enh.out))
 	}
@@ -795,13 +796,13 @@ func funcLabelJoin(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
 	for i := 3; i < len(args); i++ {
 		src := args[i].(*StringLiteral).Val
 		if !model.LabelName(src).IsValid() {
-			panic(fmt.Errorf("invalid source label name in label_join(): %s", src))
+			panic(errors.Errorf("invalid source label name in label_join(): %s", src))
 		}
 		srcLabels[i-3] = src
 	}
 
 	if !model.LabelName(dst).IsValid() {
-		panic(fmt.Errorf("invalid destination label name in label_join(): %s", dst))
+		panic(errors.Errorf("invalid destination label name in label_join(): %s", dst))
 	}
 
 	srcVals := make([]string, len(srcLabels))

promql/parse.go

@@ -23,7 +23,9 @@ import (
 	"strings"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/value"
 	"github.com/prometheus/prometheus/util/strutil"
@@ -285,7 +287,7 @@ func (p *parser) backup() {
 
 // errorf formats the error and terminates processing.
 func (p *parser) errorf(format string, args ...interface{}) {
-	p.error(fmt.Errorf(format, args...))
+	p.error(errors.Errorf(format, args...))
 }
 
 // error terminates processing.
@@ -319,7 +321,7 @@ func (p *parser) expectOneOf(exp1, exp2 ItemType, context string) item {
 	return token
 }
 
-var errUnexpected = fmt.Errorf("unexpected error")
+var errUnexpected = errors.New("unexpected error")
 
 // recover is the handler that turns panics into returns from the top level of Parse.
 func (p *parser) recover(errp *error) {
@@ -1070,7 +1072,7 @@ func parseDuration(ds string) (time.Duration, error) {
 		return 0, err
 	}
 	if dur == 0 {
-		return 0, fmt.Errorf("duration must be greater than 0")
+		return 0, errors.New("duration must be greater than 0")
 	}
 	return time.Duration(dur), nil
 }

promql/parse_test.go

@@ -14,16 +14,17 @@
 package promql
 
 import (
-	"fmt"
 	"math"
 	"reflect"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/stretchr/testify/require"
+
+	"github.com/prometheus/prometheus/pkg/labels"
 )
 
 var testExpr = []struct {
@@ -1644,7 +1645,7 @@ func mustLabelMatcher(mt labels.MatchType, name, val string) *labels.Matcher {
 func mustGetFunction(name string) *Function {
 	f, ok := getFunction(name)
 	if !ok {
-		panic(fmt.Errorf("function %q does not exist", name))
+		panic(errors.Errorf("function %q does not exist", name))
 	}
 	return f
 }
@@ -1795,7 +1796,7 @@ func TestRecoverParserError(t *testing.T) {
 	p := newParser("foo bar")
 	var err error
 
-	e := fmt.Errorf("custom error")
+	e := errors.New("custom error")
 
 	defer func() {
 		if err.Error() != e.Error() {

promql/test.go

@@ -15,7 +15,6 @@ package promql
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"math"
@@ -24,6 +23,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/pkg/labels"
@@ -102,7 +102,7 @@ func (t *Test) Storage() storage.Storage {
 func raise(line int, format string, v ...interface{}) error {
 	return &ParseErr{
 		Line: line + 1,
-		Err:  fmt.Errorf(format, v...),
+		Err:  errors.Errorf(format, v...),
 	}
 }
 
@@ -356,21 +356,21 @@ func (ev *evalCmd) expect(pos int, m labels.Labels, vals ...sequenceValue) {
 func (ev *evalCmd) compareResult(result Value) error {
 	switch val := result.(type) {
 	case Matrix:
-		return fmt.Errorf("received range result on instant evaluation")
+		return errors.New("received range result on instant evaluation")
 
 	case Vector:
 		seen := map[uint64]bool{}
 		for pos, v := range val {
 			fp := v.Metric.Hash()
 			if _, ok := ev.metrics[fp]; !ok {
-				return fmt.Errorf("unexpected metric %s in result", v.Metric)
+				return errors.Errorf("unexpected metric %s in result", v.Metric)
 			}
 			exp := ev.expected[fp]
 			if ev.ordered && exp.pos != pos+1 {
-				return fmt.Errorf("expected metric %s with %v at position %d but was at %d", v.Metric, exp.vals, exp.pos, pos+1)
+				return errors.Errorf("expected metric %s with %v at position %d but was at %d", v.Metric, exp.vals, exp.pos, pos+1)
 			}
 			if !almostEqual(exp.vals[0].value, v.V) {
-				return fmt.Errorf("expected %v for %s but got %v", exp.vals[0].value, v.Metric, v.V)
+				return errors.Errorf("expected %v for %s but got %v", exp.vals[0].value, v.Metric, v.V)
 			}
 
 			seen[fp] = true
@@ -381,17 +381,17 @@ func (ev *evalCmd) compareResult(result Value) error {
 				for _, ss := range val {
 					fmt.Println("    ", ss.Metric, ss.Point)
 				}
-				return fmt.Errorf("expected metric %s with %v not found", ev.metrics[fp], expVals)
+				return errors.Errorf("expected metric %s with %v not found", ev.metrics[fp], expVals)
 			}
 		}
 
 	case Scalar:
 		if !almostEqual(ev.expected[0].vals[0].value, val.V) {
-			return fmt.Errorf("expected Scalar %v but got %v", val.V, ev.expected[0].vals[0].value)
+			return errors.Errorf("expected Scalar %v but got %v", val.V, ev.expected[0].vals[0].value)
 		}
 
 	default:
-		panic(fmt.Errorf("promql.Test.compareResult: unexpected result type %T", result))
+		panic(errors.Errorf("promql.Test.compareResult: unexpected result type %T", result))
 	}
 	return nil
 }
@@ -447,16 +447,16 @@ func (t *Test) exec(tc testCommand) error {
 			if cmd.fail {
 				return nil
 			}
-			return fmt.Errorf("error evaluating query %q (line %d): %s", cmd.expr, cmd.line, res.Err)
+			return errors.Wrapf(res.Err, "error evaluating query %q (line %d)", cmd.expr, cmd.line)
 		}
 		defer q.Close()
 		if res.Err == nil && cmd.fail {
-			return fmt.Errorf("expected error evaluating query %q (line %d) but got none", cmd.expr, cmd.line)
+			return errors.Errorf("expected error evaluating query %q (line %d) but got none", cmd.expr, cmd.line)
 		}
 
 		err = cmd.compareResult(res.Value)
 		if err != nil {
-			return fmt.Errorf("error in %s %s: %s", cmd, cmd.expr, err)
+			return errors.Wrapf(err, "error in %s %s", cmd, cmd.expr)
 		}
 
 		// Check query returns same result in range mode,
@@ -467,7 +467,7 @@ func (t *Test) exec(tc testCommand) error {
 		}
 		rangeRes := q.Exec(t.context)
 		if rangeRes.Err != nil {
-			return fmt.Errorf("error evaluating query %q (line %d) in range mode: %s", cmd.expr, cmd.line, rangeRes.Err)
+			return errors.Wrapf(rangeRes.Err, "error evaluating query %q (line %d) in range mode", cmd.expr, cmd.line)
 		}
 		defer q.Close()
 		if cmd.ordered {
@@ -490,7 +490,7 @@ func (t *Test) exec(tc testCommand) error {
 			err = cmd.compareResult(vec)
 		}
 		if err != nil {
-			return fmt.Errorf("error in %s %s (line %d) rande mode: %s", cmd, cmd.expr, cmd.line, err)
+			return errors.Wrapf(err, "error in %s %s (line %d) rande mode", cmd, cmd.expr, cmd.line)
 		}
 
 	default:
@@ -561,7 +561,7 @@ func parseNumber(s string) (float64, error) {
 		f, err = strconv.ParseFloat(s, 64)
 	}
 	if err != nil {
-		return 0, fmt.Errorf("error parsing number: %s", err)
+		return 0, errors.Wrap(err, "error parsing number")
 	}
 	return f, nil
 }

promql/value.go

@@ -19,6 +19,8 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/pkg/errors"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/storage"
 )
@@ -215,7 +217,7 @@ func (r *Result) Vector() (Vector, error) {
 	}
 	v, ok := r.Value.(Vector)
 	if !ok {
-		return nil, fmt.Errorf("query result is not a Vector")
+		return nil, errors.New("query result is not a Vector")
 	}
 	return v, nil
 }
@@ -228,7 +230,7 @@ func (r *Result) Matrix() (Matrix, error) {
 	}
 	v, ok := r.Value.(Matrix)
 	if !ok {
-		return nil, fmt.Errorf("query result is not a range Vector")
+		return nil, errors.New("query result is not a range Vector")
 	}
 	return v, nil
 }
@@ -241,7 +243,7 @@ func (r *Result) Scalar() (Scalar, error) {
 	}
 	v, ok := r.Value.(Scalar)
 	if !ok {
-		return Scalar{}, fmt.Errorf("query result is not a Scalar")
+		return Scalar{}, errors.New("query result is not a Scalar")
 	}
 	return v, nil
 }

rules/alerting.go

@@ -26,6 +26,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/pkg/labels"
@@ -71,7 +72,7 @@ func (s AlertState) String() string {
 	case StateFiring:
 		return "firing"
 	}
-	panic(fmt.Errorf("unknown alert state: %v", s.String()))
+	panic(errors.Errorf("unknown alert state: %s", s.String()))
 }
 
 // Alert is the user-level representation of a single instance of an alerting rule.

rules/manager.go

@@ -16,7 +16,6 @@ package rules
 import (
 	"context"
 	"errors"
-	"fmt"
 	"math"
 	"net/url"
 	"sort"
@@ -29,8 +28,8 @@ import (
 	"github.com/go-kit/kit/log/level"
 	opentracing "github.com/opentracing/opentracing-go"
 	"github.com/prometheus/client_golang/prometheus"
-
 	"github.com/prometheus/common/model"
+
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/rulefmt"
 	"github.com/prometheus/prometheus/pkg/timestamp"
@@ -180,7 +179,7 @@ func EngineQueryFunc(engine *promql.Engine, q storage.Queryable) QueryFunc {
 				Metric: labels.Labels{},
 			}}, nil
 		default:
-			return nil, fmt.Errorf("rule result is not a vector or scalar")
+			return nil, errors.New("rule result is not a vector or scalar")
 		}
 	}
 }

scrape/manager.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
@@ -199,7 +200,7 @@ func (m *Manager) ApplyConfig(cfg *config.Config) error {
 	}
 
 	if failed {
-		return fmt.Errorf("failed to apply the new configuration")
+		return errors.New("failed to apply the new configuration")
 	}
 	return nil
 }

scrape/manager_test.go

@@ -14,18 +14,19 @@
 package scrape
 
 import (
-	"fmt"
 	"strconv"
 	"testing"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+	yaml "gopkg.in/yaml.v2"
+
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/relabel"
 	"github.com/prometheus/prometheus/util/testutil"
-	yaml "gopkg.in/yaml.v2"
 )
 
 func TestPopulateLabels(t *testing.T) {
@@ -127,7 +128,7 @@ func TestPopulateLabels(t *testing.T) {
 			},
 			res:     nil,
 			resOrig: nil,
-			err:     fmt.Errorf("no address"),
+			err:     errors.New("no address"),
 		},
 		// Address label missing, but added in relabelling.
 		{
@@ -206,14 +207,14 @@ func TestPopulateLabels(t *testing.T) {
 			},
 			res:     nil,
 			resOrig: nil,
-			err:     fmt.Errorf("invalid label value for \"custom\": \"\\xbd\""),
+			err:     errors.New("invalid label value for \"custom\": \"\\xbd\""),
 		},
 	}
 	for _, c := range cases {
 		in := c.in.Copy()
 
 		res, orig, err := populateLabels(c.in, c.cfg)
-		testutil.Equals(t, c.err, err)
+		testutil.ErrorEqual(err, c.err)
 		testutil.Equals(t, c.in, in)
 		testutil.Equals(t, c.res, res)
 		testutil.Equals(t, c.resOrig, orig)

scrape/scrape.go

@@ -536,7 +536,7 @@ func (s *targetScraper) scrape(ctx context.Context, w io.Writer) (string, error)
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		return "", fmt.Errorf("server returned HTTP status %s", resp.Status)
+		return "", errors.Errorf("server returned HTTP status %s", resp.Status)
 	}
 
 	if resp.Header.Get("Content-Encoding") != "gzip" {

scrape/scrape_test.go

@@ -29,6 +29,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/pkg/errors"
 	dto "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
@@ -690,7 +691,7 @@ func TestScrapeLoopRunCreatesStaleMarkersOnFailedScrape(t *testing.T) {
 		} else if numScrapes == 5 {
 			cancel()
 		}
-		return fmt.Errorf("scrape failed")
+		return errors.New("scrape failed")
 	}
 
 	go func() {
@@ -752,7 +753,7 @@ func TestScrapeLoopRunCreatesStaleMarkersOnParseFailure(t *testing.T) {
 		} else if numScrapes == 3 {
 			cancel()
 		}
-		return fmt.Errorf("scrape failed")
+		return errors.New("scrape failed")
 	}
 
 	go func() {
@@ -1079,7 +1080,7 @@ func TestScrapeLoopRunReportsTargetDownOnScrapeError(t *testing.T) {
 
 	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
 		cancel()
-		return fmt.Errorf("scrape failed")
+		return errors.New("scrape failed")
 	}
 
 	sl.run(10*time.Millisecond, time.Hour, nil)
@@ -1292,9 +1293,9 @@ func TestTargetScrapeScrapeCancel(t *testing.T) {
 	go func() {
 		_, err := ts.scrape(ctx, ioutil.Discard)
 		if err == nil {
-			errc <- fmt.Errorf("Expected error but got nil")
+			errc <- errors.New("Expected error but got nil")
 		} else if ctx.Err() != context.Canceled {
-			errc <- fmt.Errorf("Expected context cancelation error but got: %s", ctx.Err())
+			errc <- errors.Errorf("Expected context cancelation error but got: %s", ctx.Err())
 		}
 		close(errc)
 	}()

scrape/target.go

@@ -14,7 +14,6 @@
 package scrape
 
 import (
-	"errors"
 	"fmt"
 	"hash/fnv"
 	"net"
@@ -23,6 +22,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/config"
@@ -345,7 +345,7 @@ func populateLabels(lset labels.Labels, cfg *config.ScrapeConfig) (res, orig lab
 		return nil, preRelabelLabels, nil
 	}
 	if v := lset.Get(model.AddressLabel); v == "" {
-		return nil, nil, fmt.Errorf("no address")
+		return nil, nil, errors.New("no address")
 	}
 
 	lb = labels.NewBuilder(lset)
@@ -372,7 +372,7 @@ func populateLabels(lset labels.Labels, cfg *config.ScrapeConfig) (res, orig lab
 		case "https":
 			addr = addr + ":443"
 		default:
-			return nil, nil, fmt.Errorf("invalid scheme: %q", cfg.Scheme)
+			return nil, nil, errors.Errorf("invalid scheme: %q", cfg.Scheme)
 		}
 		lb.Set(model.AddressLabel, addr)
 	}
@@ -398,7 +398,7 @@ func populateLabels(lset labels.Labels, cfg *config.ScrapeConfig) (res, orig lab
 	for _, l := range res {
 		// Check label values are valid, drop the target if not.
 		if !model.LabelValue(l.Value).IsValid() {
-			return nil, nil, fmt.Errorf("invalid label value for %q: %q", l.Name, l.Value)
+			return nil, nil, errors.Errorf("invalid label value for %q: %q", l.Name, l.Value)
 		}
 	}
 	return res, preRelabelLabels, nil
@@ -424,7 +424,7 @@ func targetsFromGroup(tg *targetgroup.Group, cfg *config.ScrapeConfig) ([]*Targe
 
 		lbls, origLabels, err := populateLabels(lset, cfg)
 		if err != nil {
-			return nil, fmt.Errorf("instance %d in group %s: %s", i, tg, err)
+			return nil, errors.Wrapf(err, "instance %d in group %s", i, tg)
 		}
 		if lbls != nil || origLabels != nil {
 			targets = append(targets, NewTarget(lbls, origLabels, cfg.Params))

storage/remote/client.go

@@ -25,10 +25,11 @@ import (
 
 	"github.com/gogo/protobuf/proto"
 	"github.com/golang/snappy"
+	"github.com/pkg/errors"
+	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/version"
 
-	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/prometheus/prompb"
 )
 
@@ -102,7 +103,7 @@ func (c *Client) Store(ctx context.Context, req []byte) error {
 		if scanner.Scan() {
 			line = scanner.Text()
 		}
-		err = fmt.Errorf("server returned HTTP status %s: %s", httpResp.Status, line)
+		err = errors.Errorf("server returned HTTP status %s: %s", httpResp.Status, line)
 	}
 	if httpResp.StatusCode/100 == 5 {
 		return recoverableError{err}
@@ -126,13 +127,13 @@ func (c *Client) Read(ctx context.Context, query *prompb.Query) (*prompb.QueryRe
 	}
 	data, err := proto.Marshal(req)
 	if err != nil {
-		return nil, fmt.Errorf("unable to marshal read request: %v", err)
+		return nil, errors.Wrapf(err, "unable to marshal read request")
 	}
 
 	compressed := snappy.Encode(nil, data)
 	httpReq, err := http.NewRequest("POST", c.url.String(), bytes.NewReader(compressed))
 	if err != nil {
-		return nil, fmt.Errorf("unable to create request: %v", err)
+		return nil, errors.Wrap(err, "unable to create request")
 	}
 	httpReq.Header.Add("Content-Encoding", "snappy")
 	httpReq.Header.Add("Accept-Encoding", "snappy")
@@ -145,31 +146,31 @@ func (c *Client) Read(ctx context.Context, query *prompb.Query) (*prompb.QueryRe
 
 	httpResp, err := c.client.Do(httpReq.WithContext(ctx))
 	if err != nil {
-		return nil, fmt.Errorf("error sending request: %v", err)
+		return nil, errors.Wrap(err, "error sending request")
 	}
 	defer httpResp.Body.Close()
 	if httpResp.StatusCode/100 != 2 {
-		return nil, fmt.Errorf("server returned HTTP status %s", httpResp.Status)
+		return nil, errors.Errorf("server returned HTTP status %s", httpResp.Status)
 	}
 
 	compressed, err = ioutil.ReadAll(httpResp.Body)
 	if err != nil {
-		return nil, fmt.Errorf("error reading response: %v", err)
+		return nil, errors.Wrap(err, "error reading response")
 	}
 
 	uncompressed, err := snappy.Decode(nil, compressed)
 	if err != nil {
-		return nil, fmt.Errorf("error reading response: %v", err)
+		return nil, errors.Wrap(err, "error reading response")
 	}
 
 	var resp prompb.ReadResponse
 	err = proto.Unmarshal(uncompressed, &resp)
 	if err != nil {
-		return nil, fmt.Errorf("unable to unmarshal response body: %v", err)
+		return nil, errors.Wrap(err, "unable to unmarshal response body")
 	}
 
 	if len(resp.Results) != len(req.Queries) {
-		return nil, fmt.Errorf("responses: want %d, got %d", len(req.Queries), len(resp.Results))
+		return nil, errors.Errorf("responses: want %d, got %d", len(req.Queries), len(resp.Results))
 	}
 
 	return resp.Results[0], nil

storage/remote/client_test.go

@@ -15,17 +15,18 @@ package remote
 
 import (
 	"context"
-	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
-	"reflect"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/pkg/errors"
 	config_util "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
+
+	"github.com/prometheus/prometheus/util/testutil"
 )
 
 var longErrMessage = strings.Repeat("error message", maxErrMsgLen)
@@ -41,15 +42,15 @@ func TestStoreHTTPErrorHandling(t *testing.T) {
 		},
 		{
 			code: 300,
-			err:  fmt.Errorf("server returned HTTP status 300 Multiple Choices: " + longErrMessage[:maxErrMsgLen]),
+			err:  errors.New("server returned HTTP status 300 Multiple Choices: " + longErrMessage[:maxErrMsgLen]),
 		},
 		{
 			code: 404,
-			err:  fmt.Errorf("server returned HTTP status 404 Not Found: " + longErrMessage[:maxErrMsgLen]),
+			err:  errors.New("server returned HTTP status 404 Not Found: " + longErrMessage[:maxErrMsgLen]),
 		},
 		{
 			code: 500,
-			err:  recoverableError{fmt.Errorf("server returned HTTP status 500 Internal Server Error: " + longErrMessage[:maxErrMsgLen])},
+			err:  recoverableError{errors.New("server returned HTTP status 500 Internal Server Error: " + longErrMessage[:maxErrMsgLen])},
 		},
 	}
 
@@ -74,7 +75,7 @@ func TestStoreHTTPErrorHandling(t *testing.T) {
 		}
 
 		err = c.Store(context.Background(), []byte{})
-		if !reflect.DeepEqual(err, test.err) {
+		if !testutil.ErrorEqual(err, test.err) {
 			t.Errorf("%d. Unexpected error; want %v, got %v", i, test.err, err)
 		}
 

storage/remote/codec.go

@@ -22,6 +22,7 @@ import (
 
 	"github.com/gogo/protobuf/proto"
 	"github.com/golang/snappy"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/pkg/labels"
@@ -280,13 +281,13 @@ func (c *concreteSeriesIterator) Err() error {
 func validateLabelsAndMetricName(ls labels.Labels) error {
 	for _, l := range ls {
 		if l.Name == labels.MetricName && !model.IsValidMetricName(model.LabelValue(l.Value)) {
-			return fmt.Errorf("invalid metric name: %v", l.Value)
+			return errors.Errorf("invalid metric name: %v", l.Value)
 		}
 		if !model.LabelName(l.Name).IsValid() {
-			return fmt.Errorf("invalid label name: %v", l.Name)
+			return errors.Errorf("invalid label name: %v", l.Name)
 		}
 		if !model.LabelValue(l.Value).IsValid() {
-			return fmt.Errorf("invalid label value: %v", l.Value)
+			return errors.Errorf("invalid label value: %v", l.Value)
 		}
 	}
 	return nil
@@ -306,7 +307,7 @@ func toLabelMatchers(matchers []*labels.Matcher) ([]*prompb.LabelMatcher, error)
 		case labels.MatchNotRegexp:
 			mType = prompb.LabelMatcher_NRE
 		default:
-			return nil, fmt.Errorf("invalid matcher type")
+			return nil, errors.New("invalid matcher type")
 		}
 		pbMatchers = append(pbMatchers, &prompb.LabelMatcher{
 			Type:  mType,
@@ -331,7 +332,7 @@ func fromLabelMatchers(matchers []*prompb.LabelMatcher) ([]*labels.Matcher, erro
 		case prompb.LabelMatcher_NRE:
 			mtype = labels.MatchNotRegexp
 		default:
-			return nil, fmt.Errorf("invalid matcher type")
+			return nil, errors.New("invalid matcher type")
 		}
 		matcher, err := labels.NewMatcher(mtype, matcher.Name, matcher.Value)
 		if err != nil {

storage/remote/wal_watcher.go

@@ -27,12 +27,12 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/pkg/errors"
-
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/prometheus/pkg/timestamp"
 	"github.com/prometheus/tsdb"
 	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/wal"
+
+	"github.com/prometheus/prometheus/pkg/timestamp"
 )
 
 const (

template/template.go

@@ -16,7 +16,6 @@ package template
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"math"
 	"net/url"
@@ -28,9 +27,10 @@ import (
 	html_template "html/template"
 	text_template "text/template"
 
+	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 
-	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/util/strutil"
 )
@@ -288,7 +288,7 @@ func (te Expander) Expand() (result string, resultErr error) {
 			var ok bool
 			resultErr, ok = r.(error)
 			if !ok {
-				resultErr = fmt.Errorf("panic expanding template %v: %v", te.name, r)
+				resultErr = errors.Errorf("panic expanding template %v: %v", te.name, r)
 			}
 		}
 		if resultErr != nil {
@@ -300,12 +300,12 @@ func (te Expander) Expand() (result string, resultErr error) {
 
 	tmpl, err := text_template.New(te.name).Funcs(te.funcMap).Option("missingkey=zero").Parse(te.text)
 	if err != nil {
-		return "", fmt.Errorf("error parsing template %v: %v", te.name, err)
+		return "", errors.Wrapf(err, "error parsing template %v", te.name)
 	}
 	var buffer bytes.Buffer
 	err = tmpl.Execute(&buffer, te.data)
 	if err != nil {
-		return "", fmt.Errorf("error executing template %v: %v", te.name, err)
+		return "", errors.Wrapf(err, "error executing template %v", te.name)
 	}
 	return buffer.String(), nil
 }
@@ -317,7 +317,7 @@ func (te Expander) ExpandHTML(templateFiles []string) (result string, resultErr
 			var ok bool
 			resultErr, ok = r.(error)
 			if !ok {
-				resultErr = fmt.Errorf("panic expanding template %v: %v", te.name, r)
+				resultErr = errors.Errorf("panic expanding template %s: %v", te.name, r)
 			}
 		}
 	}()
@@ -333,18 +333,18 @@ func (te Expander) ExpandHTML(templateFiles []string) (result string, resultErr
 	})
 	tmpl, err := tmpl.Parse(te.text)
 	if err != nil {
-		return "", fmt.Errorf("error parsing template %v: %v", te.name, err)
+		return "", errors.Wrapf(err, "error parsing template %v", te.name)
 	}
 	if len(templateFiles) > 0 {
 		_, err = tmpl.ParseFiles(templateFiles...)
 		if err != nil {
-			return "", fmt.Errorf("error parsing template files for %v: %v", te.name, err)
+			return "", errors.Wrapf(err, "error parsing template files for %v", te.name)
 		}
 	}
 	var buffer bytes.Buffer
 	err = tmpl.Execute(&buffer, te.data)
 	if err != nil {
-		return "", fmt.Errorf("error executing template %v: %v", te.name, err)
+		return "", errors.Wrapf(err, "error executing template %v", te.name)
 	}
 	return buffer.String(), nil
 }

util/treecache/treecache.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/samuel/go-zookeeper/zk"
 )
@@ -195,7 +196,7 @@ func (tc *ZookeeperTreeCache) recursiveNodeUpdate(path string, node *zookeeperTr
 	if err == zk.ErrNoNode {
 		tc.recursiveDelete(path, node)
 		if node == tc.head {
-			return fmt.Errorf("path %s does not exist", path)
+			return errors.Errorf("path %s does not exist", path)
 		}
 		return nil
 	} else if err != nil {

web/api/v1/api.go

@@ -15,7 +15,6 @@ package v1
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"math"
 	"math/rand"
@@ -32,6 +31,7 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	jsoniter "github.com/json-iterator/go"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/route"
@@ -271,7 +271,7 @@ func (api *API) query(r *http.Request) apiFuncResult {
 		var err error
 		ts, err = parseTime(t)
 		if err != nil {
-			err = fmt.Errorf("invalid parameter 'time': %s", err)
+			err = errors.Wrapf(err, "invalid parameter 'time'")
 			return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 		}
 	} else {
@@ -283,7 +283,7 @@ func (api *API) query(r *http.Request) apiFuncResult {
 		var cancel context.CancelFunc
 		timeout, err := parseDuration(to)
 		if err != nil {
-			err = fmt.Errorf("invalid parameter 'timeout': %s", err)
+			err = errors.Wrapf(err, "invalid parameter 'timeout'")
 			return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 		}
 
@@ -293,7 +293,7 @@ func (api *API) query(r *http.Request) apiFuncResult {
 
 	qry, err := api.QueryEngine.NewInstantQuery(api.Queryable, r.FormValue("query"), ts)
 	if err != nil {
-		err = fmt.Errorf("invalid parameter 'query': %s", err)
+		err = errors.Wrapf(err, "invalid parameter 'query'")
 		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 	}
 
@@ -318,12 +318,12 @@ func (api *API) query(r *http.Request) apiFuncResult {
 func (api *API) queryRange(r *http.Request) apiFuncResult {
 	start, err := parseTime(r.FormValue("start"))
 	if err != nil {
-		err = fmt.Errorf("invalid parameter 'start': %s", err)
+		err = errors.Wrapf(err, "invalid parameter 'start'")
 		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 	}
 	end, err := parseTime(r.FormValue("end"))
 	if err != nil {
-		err = fmt.Errorf("invalid parameter 'end': %s", err)
+		err = errors.Wrapf(err, "invalid parameter 'end'")
 		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 	}
 	if end.Before(start) {
@@ -333,7 +333,7 @@ func (api *API) queryRange(r *http.Request) apiFuncResult {
 
 	step, err := parseDuration(r.FormValue("step"))
 	if err != nil {
-		err = fmt.Errorf("invalid parameter 'step': %s", err)
+		err = errors.Wrapf(err, "invalid parameter 'step'")
 		return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 	}
 
@@ -354,7 +354,7 @@ func (api *API) queryRange(r *http.Request) apiFuncResult {
 		var cancel context.CancelFunc
 		timeout, err := parseDuration(to)
 		if err != nil {
-			err = fmt.Errorf("invalid parameter 'timeout': %s", err)
+			err = errors.Wrap(err, "invalid parameter 'timeout'")
 			return apiFuncResult{nil, &apiError{errorBadData, err}, nil, nil}
 		}
 
@@ -421,7 +421,7 @@ func (api *API) labelValues(r *http.Request) apiFuncResult {
 	name := route.Param(ctx, "name")
 
 	if !model.LabelNameRE.MatchString(name) {
-		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("invalid label name: %q", name)}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorBadData, errors.Errorf("invalid label name: %q", name)}, nil, nil}
 	}
 	q, err := api.Queryable.Querier(ctx, math.MinInt64, math.MaxInt64)
 	if err != nil {
@@ -444,10 +444,10 @@ var (
 
 func (api *API) series(r *http.Request) apiFuncResult {
 	if err := r.ParseForm(); err != nil {
-		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing form values: %v", err)}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorBadData, errors.Wrapf(err, "error parsing form values")}, nil, nil}
 	}
 	if len(r.Form["match[]"]) == 0 {
-		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("no match[] parameter provided")}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no match[] parameter provided")}, nil, nil}
 	}
 
 	var start time.Time
@@ -511,7 +511,7 @@ func (api *API) series(r *http.Request) apiFuncResult {
 }
 
 func (api *API) dropSeries(r *http.Request) apiFuncResult {
-	return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("not implemented")}, nil, nil}
+	return apiFuncResult{nil, &apiError{errorInternal, errors.New("not implemented")}, nil, nil}
 }
 
 // Target has the information for one target.
@@ -599,7 +599,7 @@ func (api *API) targetMetadata(r *http.Request) apiFuncResult {
 	if s := r.FormValue("limit"); s != "" {
 		var err error
 		if limit, err = strconv.Atoi(s); err != nil {
-			return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("limit must be a number")}, nil, nil}
+			return apiFuncResult{nil, &apiError{errorBadData, errors.New("limit must be a number")}, nil, nil}
 		}
 	}
 
@@ -810,7 +810,7 @@ func (api *API) rules(r *http.Request) apiFuncResult {
 					Type:      "recording",
 				}
 			default:
-				err := fmt.Errorf("failed to assert type of rule '%v'", rule.Name())
+				err := errors.Errorf("failed to assert type of rule '%v'", rule.Name())
 				return apiFuncResult{nil, &apiError{errorInternal, err}, nil, nil}
 			}
 
@@ -933,10 +933,10 @@ func (api *API) deleteSeries(r *http.Request) apiFuncResult {
 	}
 
 	if err := r.ParseForm(); err != nil {
-		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("error parsing form values: %v", err)}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorBadData, errors.Wrap(err, "error parsing form values")}, nil, nil}
 	}
 	if len(r.Form["match[]"]) == 0 {
-		return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("no match[] parameter provided")}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorBadData, errors.New("no match[] parameter provided")}, nil, nil}
 	}
 
 	var start time.Time
@@ -991,7 +991,7 @@ func (api *API) snapshot(r *http.Request) apiFuncResult {
 	if r.FormValue("skip_head") != "" {
 		skipHead, err = strconv.ParseBool(r.FormValue("skip_head"))
 		if err != nil {
-			return apiFuncResult{nil, &apiError{errorBadData, fmt.Errorf("unable to parse boolean 'skip_head' argument: %v", err)}, nil, nil}
+			return apiFuncResult{nil, &apiError{errorBadData, errors.Wrapf(err, "unable to parse boolean 'skip_head' argument")}, nil, nil}
 		}
 	}
 
@@ -1008,10 +1008,10 @@ func (api *API) snapshot(r *http.Request) apiFuncResult {
 		dir = filepath.Join(snapdir, name)
 	)
 	if err := os.MkdirAll(dir, 0777); err != nil {
-		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("create snapshot directory: %s", err)}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorInternal, errors.Wrap(err, "create snapshot directory")}, nil, nil}
 	}
 	if err := db.Snapshot(dir, !skipHead); err != nil {
-		return apiFuncResult{nil, &apiError{errorInternal, fmt.Errorf("create snapshot: %s", err)}, nil, nil}
+		return apiFuncResult{nil, &apiError{errorInternal, errors.Wrap(err, "create snapshot")}, nil, nil}
 	}
 
 	return apiFuncResult{struct {
@@ -1158,21 +1158,21 @@ func parseTime(s string) (time.Time, error) {
 	if t, err := time.Parse(time.RFC3339Nano, s); err == nil {
 		return t, nil
 	}
-	return time.Time{}, fmt.Errorf("cannot parse %q to a valid timestamp", s)
+	return time.Time{}, errors.Errorf("cannot parse %q to a valid timestamp", s)
 }
 
 func parseDuration(s string) (time.Duration, error) {
 	if d, err := strconv.ParseFloat(s, 64); err == nil {
 		ts := d * float64(time.Second)
 		if ts > float64(math.MaxInt64) || ts < float64(math.MinInt64) {
-			return 0, fmt.Errorf("cannot parse %q to a valid duration. It overflows int64", s)
+			return 0, errors.Errorf("cannot parse %q to a valid duration. It overflows int64", s)
 		}
 		return time.Duration(ts), nil
 	}
 	if d, err := model.ParseDuration(s); err == nil {
 		return time.Duration(d), nil
 	}
-	return 0, fmt.Errorf("cannot parse %q to a valid duration", s)
+	return 0, errors.Errorf("cannot parse %q to a valid duration", s)
 }
 
 func marshalPointJSON(ptr unsafe.Pointer, stream *jsoniter.Stream) {

web/api/v1/api_test.go

@@ -38,6 +38,7 @@ import (
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/promlog"
 	"github.com/prometheus/common/route"
+	tsdbLabels "github.com/prometheus/tsdb/labels"
 
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/pkg/gate"
@@ -50,7 +51,6 @@ import (
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/storage/remote"
 	"github.com/prometheus/prometheus/util/testutil"
-	tsdbLabels "github.com/prometheus/tsdb/labels"
 )
 
 type testTargetRetriever struct{}
@@ -1026,7 +1026,7 @@ func (f *fakeDB) Dir() string {
 func (f *fakeDB) Snapshot(dir string, withHead bool) error { return f.err }
 
 func TestAdminEndpoints(t *testing.T) {
-	tsdb, tsdbWithError := &fakeDB{}, &fakeDB{err: fmt.Errorf("some error")}
+	tsdb, tsdbWithError := &fakeDB{}, &fakeDB{err: errors.New("some error")}
 	snapshotAPI := func(api *API) apiFunc { return api.snapshot }
 	cleanAPI := func(api *API) apiFunc { return api.cleanTombstones }
 	deleteAPI := func(api *API) apiFunc { return api.deleteSeries }

web/web.go

@@ -34,26 +34,24 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
-	"time"
-
-	"google.golang.org/grpc"
-
 	template_text "text/template"
+	"time"
 
 	"github.com/cockroachdb/cmux"
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
-	"github.com/mwitkow/go-conntrack"
+	conntrack "github.com/mwitkow/go-conntrack"
 	"github.com/opentracing-contrib/go-stdlib/nethttp"
-	"github.com/opentracing/opentracing-go"
+	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
-	"github.com/prometheus/client_model/go"
+	io_prometheus_client "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/common/route"
-	prometheus_tsdb "github.com/prometheus/prometheus/storage/tsdb"
 	"github.com/prometheus/tsdb"
 	"golang.org/x/net/netutil"
+	"google.golang.org/grpc"
 
 	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/notifier"
@@ -61,6 +59,7 @@ import (
 	"github.com/prometheus/prometheus/rules"
 	"github.com/prometheus/prometheus/scrape"
 	"github.com/prometheus/prometheus/storage"
+	prometheus_tsdb "github.com/prometheus/prometheus/storage/tsdb"
 	"github.com/prometheus/prometheus/template"
 	"github.com/prometheus/prometheus/util/httputil"
 	api_v1 "github.com/prometheus/prometheus/web/api/v1"
@@ -875,11 +874,11 @@ func (h *Handler) getTemplate(name string) (string, error) {
 
 	err := appendf("_base.html")
 	if err != nil {
-		return "", fmt.Errorf("error reading base template: %s", err)
+		return "", errors.Wrap(err, "error reading base template")
 	}
 	err = appendf(name)
 	if err != nil {
-		return "", fmt.Errorf("error reading page template %s: %s", name, err)
+		return "", errors.Wrapf(err, "error reading page template %s", name)
 	}
 
 	return tmpl, nil