[featuregate] Allow underscores in featuregate IDs

.chloggen/mx-psi_featuregate-validation.yaml

@@ -16,7 +16,7 @@ issues: [8766]
 # These lines will be padded with 2 spaces and then inserted directly into the document.
 # Use pipe (|) for multiline entries.
 subtext: |
-  Feature gates IDs are now explicitly restricted to ASCII alphanumerics and dots.
+  Feature gates IDs are now explicitly restricted to ASCII alphanumerics, underscores and dots.
 
 # Optional: The change log or logs in which this entry should be included.
 # e.g. '[user]' or '[user, api]'

featuregate/registry.go

@@ -18,8 +18,8 @@ var (
 	globalRegistry = NewRegistry()
 
 	// idRegexp is used to validate the ID of a Gate.
-	// IDs' characters must be alphanumeric or dots.
-	idRegexp = regexp.MustCompile(`^[0-9a-zA-Z\.]*$`)
+	// IDs' characters must be alphanumeric, underscores or dots.
+	idRegexp = regexp.MustCompile(`^[0-9a-zA-Z_\.]*$`)
 )
 
 // GlobalRegistry returns the global Registry.
@@ -122,7 +122,7 @@ func validateID(id string) error {
 }
 
 // Register a Gate and return it. The returned Gate can be used to check if is enabled or not.
-// id must be an ASCII alphanumeric nonempty string. Dots are allowed for namespacing.
+// id must be an ASCII alphanumeric nonempty string. Dots are allowed for namespacing and underscores for snake casing.
 func (r *Registry) Register(id string, stage Stage, opts ...RegisterOption) (*Gate, error) {
 	if err := validateID(id); err != nil {
 		return nil, fmt.Errorf("invalid ID %q: %w", id, err)

featuregate/registry_test.go

@@ -152,6 +152,12 @@ func TestRegisterGateLifecycle(t *testing.T) {
 			stage:     StageAlpha,
 			shouldErr: true,
 		},
+		{
+			name:      "Gate name with underscores",
+			id:        "gcp.untyped_double_export",
+			stage:     StageAlpha,
+			shouldErr: false,
+		},
 		{
 			name:      "Invalid empty gate",
 			id:        "",