Test template expansion while loading groups (#4537)

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

pkg/rulefmt/rulefmt.go

@@ -14,11 +14,16 @@
 package rulefmt
 
 import (
+	"context"
+	"fmt"
 	"io/ioutil"
+	"time"
 
 	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/pkg/timestamp"
 	"github.com/prometheus/prometheus/promql"
+	"github.com/prometheus/prometheus/template"
 	yaml "gopkg.in/yaml.v2"
 )
 
@@ -137,6 +142,50 @@ func (r *Rule) Validate() (errs []error) {
 		}
 	}
 
+	errs = append(errs, testTemplateParsing(r)...)
+	return errs
+}
+
+// testTemplateParsing checks if the templates used in labels and annotations
+// of the alerting rules are parsed correctly.
+func testTemplateParsing(rl *Rule) (errs []error) {
+	if rl.Alert == "" {
+		// Not an alerting rule.
+		return errs
+	}
+
+	// Trying to parse templates.
+	tmplData := template.AlertTemplateData(make(map[string]string), 0)
+	defs := "{{$labels := .Labels}}{{$value := .Value}}"
+	parseTest := func(text string) error {
+		tmpl := template.NewTemplateExpander(
+			context.TODO(),
+			defs+text,
+			"__alert_"+rl.Alert,
+			tmplData,
+			model.Time(timestamp.FromTime(time.Now())),
+			nil,
+			nil,
+		)
+		return tmpl.ParseTest()
+	}
+
+	// Parsing Labels.
+	for _, val := range rl.Labels {
+		err := parseTest(val)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("msg=%s", err.Error()))
+		}
+	}
+
+	// Parsing Annotations.
+	for _, val := range rl.Annotations {
+		err := parseTest(val)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("msg=%s", err.Error()))
+		}
+	}
+
 	return errs
 }
 

pkg/rulefmt/rulefmt_test.go

@@ -17,6 +17,8 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+
+	"github.com/prometheus/prometheus/util/testutil"
 )
 
 func TestParseFileSuccess(t *testing.T) {
@@ -79,3 +81,83 @@ func TestParseFileFailure(t *testing.T) {
 	}
 
 }
+
+func TestTemplateParsing(t *testing.T) {
+	tests := []struct {
+		ruleString string
+		shouldPass bool
+	}{
+		{
+			ruleString: `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 5m
+    labels:
+      severity: "page"
+    annotations:
+      summary: "Instance {{ $labels.instance }} down"
+`,
+			shouldPass: true,
+		},
+		{
+			// `$label` instead of `$labels`.
+			ruleString: `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 5m
+    labels:
+      severity: "page"
+    annotations:
+      summary: "Instance {{ $label.instance }} down"
+`,
+			shouldPass: false,
+		},
+		{
+			// `$this_is_wrong`.
+			ruleString: `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 5m
+    labels:
+      severity: "{{$this_is_wrong}}"
+    annotations:
+      summary: "Instance {{ $labels.instance }} down"
+`,
+			shouldPass: false,
+		},
+		{
+			// `$labels.quantile * 100`.
+			ruleString: `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 5m
+    labels:
+      severity: "page"
+    annotations:
+      summary: "Instance {{ $labels.instance }} down"
+      description: "{{$labels.quantile * 100}}"
+`,
+			shouldPass: false,
+		},
+	}
+
+	for _, tst := range tests {
+		rgs, errs := Parse([]byte(tst.ruleString))
+		testutil.Assert(t, rgs != nil, "Rule parsing, rule=\n"+tst.ruleString)
+		passed := (tst.shouldPass && len(errs) == 0) || (!tst.shouldPass && len(errs) > 0)
+		testutil.Assert(t, passed, "Rule validation failed, rule=\n"+tst.ruleString)
+	}
+
+}

rules/alerting.go

@@ -292,13 +292,7 @@ func (r *AlertingRule) Eval(ctx context.Context, ts time.Time, query QueryFunc,
 			l[lbl.Name] = lbl.Value
 		}
 
-		tmplData := struct {
-			Labels map[string]string
-			Value  float64
-		}{
-			Labels: l,
-			Value:  smpl.V,
-		}
+		tmplData := template.AlertTemplateData(l, smpl.V)
 		// Inject some convenience variables that are easier to remember for users
 		// who are not used to Go's templating system.
 		defs := "{{$labels := .Labels}}{{$value := .Value}}"

template/template.go

@@ -243,6 +243,17 @@ func NewTemplateExpander(
 	}
 }
 
+// AlertTemplateData returns the interface to be used in expanding the template.
+func AlertTemplateData(labels map[string]string, value float64) interface{} {
+	return struct {
+		Labels map[string]string
+		Value  float64
+	}{
+		Labels: labels,
+		Value:  value,
+	}
+}
+
 // Funcs adds the functions in fm to the Expander's function map.
 // Existing functions will be overwritten in case of conflict.
 func (te Expander) Funcs(fm text_template.FuncMap) {
@@ -315,3 +326,12 @@ func (te Expander) ExpandHTML(templateFiles []string) (result string, resultErr
 	}
 	return buffer.String(), nil
 }
+
+// ParseTest parses the templates and returns the error if any.
+func (te Expander) ParseTest() error {
+	_, err := text_template.New(te.name).Funcs(te.funcMap).Option("missingkey=zero").Parse(te.text)
+	if err != nil {
+		return err
+	}
+	return nil
+}