Add parse alerting for rules files (#16601)

Builds over https://github.com/prometheus/prometheus/pull/16462
Addresses comments, adds invalid rules file

Signed-off-by: subhramit <subhramit.bb@live.in>
Co-authored-by: marcodebba <marcodebonis74@gmail.com>

cmd/prometheus/main.go

@@ -648,6 +648,17 @@ func main() {
 		logger.Error(fmt.Sprintf("Error loading dynamic scrape config files from config (--config.file=%q)", cfg.configFile), "file", absPath, "err", err)
 		os.Exit(2)
 	}
+
+	// Parse rule files to verify they exist and contain valid rules.
+	if err := rules.ParseFiles(cfgFile.RuleFiles); err != nil {
+		absPath, pathErr := filepath.Abs(cfg.configFile)
+		if pathErr != nil {
+			absPath = cfg.configFile
+		}
+		logger.Error(fmt.Sprintf("Error loading rule file patterns from config (--config.file=%q)", cfg.configFile), "file", absPath, "err", err)
+		os.Exit(2)
+	}
+
 	if cfg.tsdb.EnableExemplarStorage {
 		if cfgFile.StorageConfig.ExemplarsConfig == nil {
 			cfgFile.StorageConfig.ExemplarsConfig = &config.DefaultExemplarsConfig

rules/fixtures/invalid_rules.yaml

@@ -0,0 +1,6 @@
+groups:
+  - name: invalid
+    rules:
+      - record: job:http_requests:rate5m
+        expr: sum by (job)(rate(http_requests_total[5m]))
+        unexpected_field: this_field_should_not_be_here

rules/manager.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net/url"
+	"path/filepath"
 	"slices"
 	"strings"
 	"sync"
@@ -579,3 +580,32 @@ func FromMaps(maps ...map[string]string) labels.Labels {
 
 	return labels.FromMap(mLables)
 }
+
+// ParseFiles parses the rule files corresponding to glob patterns.
+func ParseFiles(patterns []string) error {
+	files := map[string]string{}
+	for _, pat := range patterns {
+		fns, err := filepath.Glob(pat)
+		if err != nil {
+			return fmt.Errorf("failed retrieving rule files for %q: %w", pat, err)
+		}
+		for _, fn := range fns {
+			absPath, err := filepath.Abs(fn)
+			if err != nil {
+				absPath = fn
+			}
+			cleanPath, err := filepath.EvalSymlinks(absPath)
+			if err != nil {
+				return fmt.Errorf("failed evaluating rule file path %q (pattern: %q): %w", absPath, pat, err)
+			}
+			files[cleanPath] = pat
+		}
+	}
+	for fn, pat := range files {
+		_, errs := rulefmt.ParseFile(fn, false)
+		if len(errs) > 0 {
+			return fmt.Errorf("parse rules from file %q (pattern: %q): %w", fn, pat, errors.Join(errs...))
+		}
+	}
+	return nil
+}

rules/manager_test.go

@@ -20,6 +20,7 @@ import (
 	"math"
 	"os"
 	"path"
+	"path/filepath"
 	"slices"
 	"sort"
 	"strconv"
@@ -2549,6 +2550,17 @@ func TestLabels_FromMaps(t *testing.T) {
 	require.Equal(t, expected, mLabels, "unexpected labelset")
 }
 
+func TestParseFiles(t *testing.T) {
+	t.Run("good files", func(t *testing.T) {
+		err := ParseFiles([]string{filepath.Join("fixtures", "rules.y*ml")})
+		require.NoError(t, err)
+	})
+	t.Run("bad files", func(t *testing.T) {
+		err := ParseFiles([]string{filepath.Join("fixtures", "invalid_rules.y*ml")})
+		require.ErrorContains(t, err, "field unexpected_field not found in type rulefmt.Rule")
+	})
+}
+
 func TestRuleDependencyController_AnalyseRules(t *testing.T) {
 	type expectedDependencies struct {
 		noDependentRules  bool