feat(AIP-133): ignore create methods with invalid LRO response types (#…

…1366)

* feat(AIP-133): ignore create methods with invalid LRO response types

* chore: clean up return type resolution logic

rules/aip0133/request_required_fields.go

@@ -28,7 +28,7 @@ import (
 // The create request message should not have unrecognized fields.
 var requestRequiredFields = &lint.MethodRule{
 	Name:   lint.NewRuleName(133, "request-required-fields"),
-	OnlyIf: utils.IsCreateMethod,
+	OnlyIf: utils.IsCreateMethodWithResolvedReturnType,
 	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
 		ot := utils.GetResponseType(m)
 		r := utils.GetResource(ot)

rules/internal/utils/method.go

@@ -36,6 +36,18 @@ func IsCreateMethod(m *desc.MethodDescriptor) bool {
 	return createMethodRegexp.MatchString(m.GetName())
 }
 
+// IsCreateMethod returns true if this is a AIP-133 Create method with
+// a non-nil response type. This method should be used for filtering in linter
+// rules which access the response type of the method, to avoid crashing due
+// to dereferencing a nil pointer to the response.
+func IsCreateMethodWithResolvedReturnType(m *desc.MethodDescriptor) bool {
+	if !IsCreateMethod(m) {
+		return false
+	}
+
+	return GetResponseType(m) != nil
+}
+
 // IsGetMethod returns true if this is a AIP-131 Get method.
 func IsGetMethod(m *desc.MethodDescriptor) bool {
 	methodName := m.GetName()