rulefmt: warn when multi-document rule files are detected (#18114)

Signed-off-by: Divyansh Mishra <divyanshmishra@Divyanshs-MacBook-Air-3.local>
Co-authored-by: Divyansh Mishra <mishraa-G@users.noreply.github.com>
Co-authored-by: Divyansh Mishra <divyanshmishra@Divyanshs-MacBook-Air-3.local>

model/rulefmt/rulefmt.go

@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"os"
 	"strings"
 	"time"
@@ -339,7 +340,13 @@ func testTemplateParsing(rl *Rule) (errs []error) {
 }
 
 // Parse parses and validates a set of rules.
-func Parse(content []byte, ignoreUnknownFields bool, nameValidationScheme model.ValidationScheme, p parser.Parser) (*RuleGroups, []error) {
+func Parse(
+	content []byte,
+	ignoreUnknownFields bool,
+	nameValidationScheme model.ValidationScheme,
+	p parser.Parser,
+	logger *slog.Logger,
+) (*RuleGroups, []error) {
 	var (
 		groups RuleGroups
 		node   ruleGroups
@@ -355,6 +362,13 @@ func Parse(content []byte, ignoreUnknownFields bool, nameValidationScheme model.
 	if err != nil && !errors.Is(err, io.EOF) {
 		errs = append(errs, err)
 	}
+	// Check for a second document.
+	var secondDoc any
+	err = decoder.Decode(&secondDoc)
+	if !errors.Is(err, io.EOF) {
+		logger.Warn("Multiple document yaml rules files are not supported, only the first document is processed")
+	}
+
 	err = yaml.Unmarshal(content, &node)
 	if err != nil {
 		errs = append(errs, err)
@@ -368,12 +382,18 @@ func Parse(content []byte, ignoreUnknownFields bool, nameValidationScheme model.
 }
 
 // ParseFile reads and parses rules from a file.
-func ParseFile(file string, ignoreUnknownFields bool, nameValidationScheme model.ValidationScheme, p parser.Parser) (*RuleGroups, []error) {
+func ParseFile(
+	file string,
+	ignoreUnknownFields bool,
+	nameValidationScheme model.ValidationScheme,
+	p parser.Parser,
+	logger *slog.Logger,
+) (*RuleGroups, []error) {
 	b, err := os.ReadFile(file)
 	if err != nil {
 		return nil, []error{fmt.Errorf("%s: %w", file, err)}
 	}
-	rgs, errs := Parse(b, ignoreUnknownFields, nameValidationScheme, p)
+	rgs, errs := Parse(b, ignoreUnknownFields, nameValidationScheme, p, logger)
 	for i := range errs {
 		errs[i] = fmt.Errorf("%s: %w", file, errs[i])
 	}

model/rulefmt/rulefmt_test.go

@@ -14,29 +14,35 @@
 package rulefmt
 
 import (
+	"bytes"
 	"errors"
 	"io"
+	"log/slog"
 	"path/filepath"
 	"testing"
 
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/common/promslog"
 	"github.com/stretchr/testify/require"
 	"go.yaml.in/yaml/v3"
 
 	"github.com/prometheus/prometheus/promql/parser"
 )
 
-var testParser = parser.NewParser(parser.Options{})
+var (
+	testParser = parser.NewParser(parser.Options{})
+	testLogger = promslog.NewNopLogger()
+)
 
 func TestParseFileSuccess(t *testing.T) {
-	_, errs := ParseFile("testdata/test.yaml", false, model.UTF8Validation, testParser)
+	_, errs := ParseFile("testdata/test.yaml", false, model.UTF8Validation, testParser, testLogger)
 	require.Empty(t, errs, "unexpected errors parsing file")
 
-	_, errs = ParseFile("testdata/utf-8_lname.good.yaml", false, model.UTF8Validation, testParser)
+	_, errs = ParseFile("testdata/utf-8_lname.good.yaml", false, model.UTF8Validation, testParser, testLogger)
 	require.Empty(t, errs, "unexpected errors parsing file")
-	_, errs = ParseFile("testdata/utf-8_annotation.good.yaml", false, model.UTF8Validation, testParser)
+	_, errs = ParseFile("testdata/utf-8_annotation.good.yaml", false, model.UTF8Validation, testParser, testLogger)
 	require.Empty(t, errs, "unexpected errors parsing file")
-	_, errs = ParseFile("testdata/legacy_validation_annotation.good.yaml", false, model.LegacyValidation, testParser)
+	_, errs = ParseFile("testdata/legacy_validation_annotation.good.yaml", false, model.LegacyValidation, testParser, testLogger)
 	require.Empty(t, errs, "unexpected errors parsing file")
 }
 
@@ -45,7 +51,7 @@ func TestParseFileSuccessWithAliases(t *testing.T) {
 /
 sum without(instance) (rate(requests_total[5m]))
 `
-	rgs, errs := ParseFile("testdata/test_aliases.yaml", false, model.UTF8Validation, testParser)
+	rgs, errs := ParseFile("testdata/test_aliases.yaml", false, model.UTF8Validation, testParser, testLogger)
 	require.Empty(t, errs, "unexpected errors parsing file")
 	for _, rg := range rgs.Groups {
 		require.Equal(t, "HighAlert", rg.Rules[0].Alert)
@@ -123,7 +129,7 @@ func TestParseFileFailure(t *testing.T) {
 			if c.nameValidationScheme == model.UnsetValidation {
 				c.nameValidationScheme = model.UTF8Validation
 			}
-			_, errs := ParseFile(filepath.Join("testdata", c.filename), false, c.nameValidationScheme, testParser)
+			_, errs := ParseFile(filepath.Join("testdata", c.filename), false, c.nameValidationScheme, testParser, testLogger)
 			require.NotEmpty(t, errs, "Expected error parsing %s but got none", c.filename)
 			require.ErrorContainsf(t, errs[0], c.errMsg, "Expected error for %s.", c.filename)
 		})
@@ -219,7 +225,7 @@ groups:
 	}
 
 	for _, tst := range tests {
-		rgs, errs := Parse([]byte(tst.ruleString), false, model.UTF8Validation, testParser)
+		rgs, errs := Parse([]byte(tst.ruleString), false, model.UTF8Validation, testParser, testLogger)
 		require.NotNil(t, rgs, "Rule parsing, rule=\n"+tst.ruleString)
 		passed := (tst.shouldPass && len(errs) == 0) || (!tst.shouldPass && len(errs) > 0)
 		require.True(t, passed, "Rule validation failed, rule=\n"+tst.ruleString)
@@ -246,7 +252,7 @@ groups:
     annotations:
       summary: "Instance {{ $labels.instance }} up"
 `
-	_, errs := Parse([]byte(group), false, model.UTF8Validation, testParser)
+	_, errs := Parse([]byte(group), false, model.UTF8Validation, testParser, testLogger)
 	require.Len(t, errs, 2, "Expected two errors")
 	var err00 *Error
 	require.ErrorAs(t, errs[0], &err00)
@@ -391,3 +397,59 @@ func TestErrorUnwrap(t *testing.T) {
 		})
 	}
 }
+
+func TestMultiDocParse(t *testing.T) {
+	const (
+		valid = `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+`
+		multi = `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+---
+groups:
+- name: example2
+  rules:
+  - alert: InstanceDown2
+    expr: up == 0
+`
+		multiEmpty = `
+groups:
+- name: example
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+---
+`
+	)
+
+	var buf bytes.Buffer
+	bufLogger := slog.New(slog.NewTextHandler(&buf, nil))
+
+	rgs, errs := Parse([]byte(valid), false, model.UTF8Validation, testParser, bufLogger)
+	require.Empty(t, errs)
+	require.NotNil(t, rgs)
+	require.Len(t, rgs.Groups, 1)
+	require.NotContains(t, buf.String(), "Multiple document yaml rules files are not supported")
+	buf.Reset()
+
+	rgs, errs = Parse([]byte(multi), false, model.UTF8Validation, testParser, bufLogger)
+	require.Empty(t, errs)
+	require.NotNil(t, rgs)
+	require.Len(t, rgs.Groups, 1)
+	require.Contains(t, buf.String(), "Multiple document yaml rules files are not supported")
+	buf.Reset()
+
+	rgs, errs = Parse([]byte(multiEmpty), false, model.UTF8Validation, testParser, bufLogger)
+	require.Empty(t, errs)
+	require.NotNil(t, rgs)
+	require.Len(t, rgs.Groups, 1)
+	require.Contains(t, buf.String(), "Multiple document yaml rules files are not supported")
+}