Allow calling DecodeRuleConfig without rule config

hclext/structure.go

@@ -158,6 +158,14 @@ func PartialContent(body hcl.Body, schema *BodySchema) (*BodyContent, hcl.Diagno
 	return ret, diags
 }
 
+// IsEmpty returns whether the body content is empty
+func (b *BodyContent) IsEmpty() bool {
+	if b == nil {
+		return true
+	}
+	return len(b.Attributes) == 0 && len(b.Blocks) == 0
+}
+
 // AsNative returns self as hcl.Attributes
 func (as Attributes) AsNative() hcl.Attributes {
 	ret := hcl.Attributes{}

hclext/structure_test.go

@@ -695,3 +695,44 @@ func TestContent_PartialContent(t *testing.T) {
 		})
 	}
 }
+
+func Test_IsEmpty(t *testing.T) {
+	tests := []struct {
+		name string
+		body *BodyContent
+		want bool
+	}{
+		{
+			name: "body is not empty",
+			body: &BodyContent{
+				Attributes: Attributes{
+					"foo": &Attribute{Name: "foo"},
+				},
+			},
+			want: false,
+		},
+		{
+			name: "body has empty attributes and empty blocks",
+			body: &BodyContent{Attributes: Attributes{}, Blocks: Blocks{}},
+			want: true,
+		},
+		{
+			name: "body has nil attributes and nil blocks",
+			body: &BodyContent{},
+			want: true,
+		},
+		{
+			name: "body is nil",
+			body: nil,
+			want: true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if test.body.IsEmpty() != test.want {
+				t.Errorf("%t is expected, but got %t", test.want, test.body.IsEmpty())
+			}
+		})
+	}
+}

helper/runner.go

@@ -141,7 +141,7 @@ func (r *Runner) DecodeRuleConfig(name string, ret interface{}) error {
 		}
 	}
 
-	return fmt.Errorf("rule `%s` not found", name)
+	return nil
 }
 
 // EvaluateExpr returns a value of the passed expression.

helper/runner_test.go

@@ -280,6 +280,46 @@ func Test_GetModuleContent_json(t *testing.T) {
 	}
 }
 
+func Test_DecodeRuleConfig(t *testing.T) {
+	files := map[string]string{
+		".tflint.hcl": `
+rule "test" {
+  enabled = true
+  foo     = "bar"
+}`,
+	}
+
+	runner := TestRunner(t, files)
+
+	type ruleConfig struct {
+		Foo string `hclext:"foo"`
+	}
+	target := &ruleConfig{}
+	if err := runner.DecodeRuleConfig("test", target); err != nil {
+		t.Fatal(err)
+	}
+
+	if target.Foo != "bar" {
+		t.Errorf("target.Foo should be `bar`, but got `%s`", target.Foo)
+	}
+}
+
+func Test_DecodeRuleConfig_config_not_found(t *testing.T) {
+	runner := TestRunner(t, map[string]string{})
+
+	type ruleConfig struct {
+		Foo string `hclext:"foo"`
+	}
+	target := &ruleConfig{}
+	if err := runner.DecodeRuleConfig("test", target); err != nil {
+		t.Fatal(err)
+	}
+
+	if target.Foo != "" {
+		t.Errorf("target.Foo should be empty, but got `%s`", target.Foo)
+	}
+}
+
 func Test_EvaluateExpr(t *testing.T) {
 	tests := []struct {
 		Name string

plugin/plugin2host/client.go

@@ -180,6 +180,10 @@ func (c *GRPCClient) DecodeRuleConfig(name string, ret interface{}) error {
 	if diags.HasErrors() {
 		return diags
 	}
+	if content.IsEmpty() {
+		return nil
+	}
+
 	diags = hclext.DecodeBody(content, nil, ret)
 	if diags.HasErrors() {
 		return diags

plugin/plugin2host/plugin2host_test.go

@@ -984,6 +984,16 @@ rule "test_rule" {
 			ServerImpl: func(name string, schema *hclext.BodySchema) (*hclext.BodyContent, map[string][]byte, error) {
 				return &hclext.BodyContent{}, nil, nil
 			},
+			Want:     &ruleConfig{},
+			ErrCheck: neverHappend,
+		},
+		{
+			Name:     "config not found with non-empty config",
+			RuleName: "not_found",
+			Target:   &ruleConfig{},
+			ServerImpl: func(name string, schema *hclext.BodySchema) (*hclext.BodyContent, map[string][]byte, error) {
+				return &hclext.BodyContent{Attributes: hclext.Attributes{"foo": &hclext.Attribute{}}}, nil, nil
+			},
 			Want: &ruleConfig{},
 			ErrCheck: func(err error) bool {
 				return err == nil || err.Error() != "config file not found"

plugin/plugin2host/server.go

@@ -102,7 +102,7 @@ func (s *GRPCServer) GetRuleConfigContent(ctx context.Context, req *proto.GetRul
 	if body == nil {
 		return nil, status.Error(codes.FailedPrecondition, "response body is empty")
 	}
-	if len(sources) == 0 {
+	if len(sources) == 0 && !body.IsEmpty() {
 		return nil, status.Error(codes.NotFound, "config file not found")
 	}