Add simple rule file checker tool.

This tool does the simple job of checking a Prometheus rule file for validity
and printing the parsed rules if the loading succeeds. This came out of
an immediate need to quickly verify changes to existing rule files.

tools/Makefile

@@ -11,7 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-all: dumper pruner
+all: dumper pruner rule_checker
 
 SUFFIXES:
 
@@ -23,8 +23,12 @@ dumper:
 pruner:
 	$(MAKE) -C pruner
 
+rule_checker:
+	$(MAKE) -C rule_checker
+
 clean:
 	$(MAKE) -C dumper clean
 	$(MAKE) -C pruner clean
+	$(MAKE) -C rule_checker clean
 
-.PHONY: clean dumper pruner
+.PHONY: clean dumper pruner rule_checker

tools/rule_checker/.gitignore

@@ -0,0 +1 @@
+rule_checker

tools/rule_checker/Makefile

@@ -0,0 +1,28 @@
+# Copyright 2013 Prometheus Team
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+MAKE_ARTIFACTS = rule_checker
+
+all: rule_checker
+
+SUFFIXES:
+
+include ../../Makefile.INCLUDE
+
+rule_checker: $(shell find . -iname '*.go')
+	$(GO) build -o rule_checker .
+
+clean:
+	rm -rf $(MAKE_ARTIFACTS)
+
+.PHONY: clean

tools/rule_checker/main.go

@@ -0,0 +1,46 @@
+// Copyright 2013 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Rule-Checker allows checking the validity of a Prometheus rule file. It
+// prints an error if the specified rule file is invalid, while it prints a
+// string representation of the parsed rules otherwise.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+
+	"github.com/prometheus/prometheus/rules"
+)
+
+var ruleFile = flag.String("ruleFile", "", "The path to the rule file to check.")
+
+func main() {
+	flag.Parse()
+
+	if *ruleFile == "" {
+		log.Fatal("Must provide a rule file path")
+	}
+
+	rules, err := rules.LoadRulesFromFile(*ruleFile)
+	if err != nil {
+		log.Fatalf("Error loading rule file %s: %s", *ruleFile, err)
+	}
+
+	fmt.Printf("Successfully loaded %d rules:\n\n", len(rules))
+
+	for _, rule := range rules {
+		fmt.Println(rule)
+	}
+}