Fix UTF-8 not allowed in Equal field for inhibition rules

This commit fixes a bug where UTF-8 characters are not allowed
in the Equal field for inhibition rules, even when UTF-8 strict
mode is enabled.

This bug occurred because we forgot to override the validation
in model.LabelName. I have copied the same logic used for
GroupBy with GroupByStr, adding EqualByStr.

We would like to upgrade prometheus/common in future and use
the validation there instead, but it presents challenges with
downstream projects like Mimir and Cortex where, at present,
UTF-8 can be enabled and disabled in separate components at the
same time, which is not supported in prometheus/common.

Signed-off-by: George Robinson <[email protected]>

config/config.go

@@ -942,7 +942,11 @@ type InhibitRule struct {
 	TargetMatchers Matchers `yaml:"target_matchers,omitempty" json:"target_matchers,omitempty"`
 	// A set of labels that must be equal between the source and target alert
 	// for them to be a match.
-	Equal model.LabelNames `yaml:"equal,omitempty" json:"equal,omitempty"`
+	Equal model.LabelNames `yaml:"-" json:"-"`
+	// EqualStr allows us to validate the label depending on whether UTF-8 is
+	// enabled or disabled. It should be removed when Alertmanager is updated
+	// to use the switchable validation in recent versions of prometheus/common.
+	EqualStr []string `yaml:"equal,omitempty" json:"equal,omitempty"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface for InhibitRule.
@@ -964,6 +968,14 @@ func (r *InhibitRule) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		}
 	}
 
+	for _, l := range r.EqualStr {
+		labelName := model.LabelName(l)
+		if !compat.IsValidLabelName(labelName) {
+			return fmt.Errorf("invalid label name %q in equal list", l)
+		}
+		r.Equal = append(r.Equal, labelName)
+	}
+
 	return nil
 }
 

config/config_test.go

@@ -25,8 +25,12 @@ import (
 
 	commoncfg "github.com/prometheus/common/config"
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/common/promslog"
 	"github.com/stretchr/testify/require"
 	"gopkg.in/yaml.v2"
+
+	"github.com/prometheus/alertmanager/featurecontrol"
+	"github.com/prometheus/alertmanager/matcher/compat"
 )
 
 func TestLoadEmptyString(t *testing.T) {
@@ -1387,3 +1391,39 @@ func TestNilRegexp(t *testing.T) {
 		})
 	}
 }
+
+func TestInhibitRuleEqual(t *testing.T) {
+	_, err := LoadFile("testdata/conf.inhibit-equal.yml")
+	if err != nil {
+		t.Errorf("Error parsing %s: %s", "testdata/conf.inhibit-equal.yml", err)
+	}
+	// Should not be able to load configuration with UTF-8 in equals
+	_, err = LoadFile("testdata/conf.inhibit-equal-utf8.yml")
+	if err == nil {
+		t.Errorf("Expected error parsing %s, got nil", "testdata/conf.inhibit-equal-utf8.yml")
+	}
+	expected := "invalid label name \"qux🙂\" in equal list"
+	if err.Error() != expected {
+		t.Errorf("Expected error \n%s, got \n%s", expected, err)
+	}
+
+	// Change the mode to UTF-8 mode.
+	ff, err := featurecontrol.NewFlags(promslog.NewNopLogger(), featurecontrol.FeatureUTF8StrictMode)
+	require.NoError(t, err)
+	compat.InitFromFlags(promslog.NewNopLogger(), ff)
+
+	// Restore the mode to classic at the end of the test.
+	ff, err = featurecontrol.NewFlags(promslog.NewNopLogger(), featurecontrol.FeatureClassicMode)
+	require.NoError(t, err)
+	defer compat.InitFromFlags(promslog.NewNopLogger(), ff)
+
+	_, err = LoadFile("testdata/conf.inhibit-equal.yml")
+	if err != nil {
+		t.Errorf("Error parsing %s: %s", "testdata/conf.inhibit-equal.yml", err)
+	}
+	// Should also be able to load configuration with UTF-8 in equals
+	_, err = LoadFile("testdata/conf.inhibit-equal-utf8.yml")
+	if err != nil {
+		t.Errorf("Error parsing %s: %s", "testdata/conf.inhibit-equal-utf8.yml", err)
+	}
+}

config/testdata/conf.inhibit-equal-utf8.yml

@@ -0,0 +1,10 @@
+route:
+  receiver: test
+receivers:
+  - name: test
+inhibit_rules:
+  - source_matchers:
+    - foo=bar
+    target_matchers:
+    - bar=baz
+    equal: ['qux🙂']

config/testdata/conf.inhibit-equal.yml

@@ -0,0 +1,10 @@
+route:
+  receiver: test
+receivers:
+  - name: test
+inhibit_rules:
+  - source_matchers:
+    - foo=bar
+    target_matchers:
+    - bar=baz
+    equal: ['qux']