config: parsing of local.foo variables for interpolation

config/interpolate.go

@@ -101,6 +101,12 @@ type UserVariable struct {
 	key string
 }
 
+// A LocalVariable is a variable that references a local value defined within
+// the current module, via a "locals" block. This looks like "${local.foo}".
+type LocalVariable struct {
+	Name string
+}
+
 func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
 	if strings.HasPrefix(v, "count.") {
 		return NewCountVariable(v)
@@ -112,6 +118,8 @@ func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
 		return NewTerraformVariable(v)
 	} else if strings.HasPrefix(v, "var.") {
 		return NewUserVariable(v)
+	} else if strings.HasPrefix(v, "local.") {
+		return NewLocalVariable(v)
 	} else if strings.HasPrefix(v, "module.") {
 		return NewModuleVariable(v)
 	} else if !strings.ContainsRune(v, '.') {
@@ -331,6 +339,25 @@ func (v *UserVariable) GoString() string {
 	return fmt.Sprintf("*%#v", *v)
 }
 
+func NewLocalVariable(key string) (*LocalVariable, error) {
+	name := key[len("local."):]
+	if idx := strings.Index(name, "."); idx > -1 {
+		return nil, fmt.Errorf("Can't use dot (.) attribute access in local.%s; use square bracket indexing", name)
+	}
+
+	return &LocalVariable{
+		Name: name,
+	}, nil
+}
+
+func (v *LocalVariable) FullKey() string {
+	return fmt.Sprintf("local.%s", v.Name)
+}
+
+func (v *LocalVariable) GoString() string {
+	return fmt.Sprintf("*%#v", *v)
+}
+
 // DetectVariables takes an AST root and returns all the interpolated
 // variables that are detected in the AST tree.
 func DetectVariables(root ast.Node) ([]InterpolatedVariable, error) {

config/interpolate_test.go

@@ -9,9 +9,9 @@ import (
 )
 
 func TestNewInterpolatedVariable(t *testing.T) {
-	cases := []struct {
+	tests := []struct {
 		Input string
-		Result InterpolatedVariable
+		Want  InterpolatedVariable
 		Error bool
 	}{
 		{
@@ -22,6 +22,18 @@ func TestNewInterpolatedVariable(t *testing.T) {
 			},
 			false,
 		},
+		{
+			"local.foo",
+			&LocalVariable{
+				Name: "foo",
+			},
+			false,
+		},
+		{
+			"local.foo.nope",
+			nil,
+			true,
+		},
 		{
 			"module.foo.bar",
 			&ModuleVariable{
@@ -73,14 +85,19 @@ func TestNewInterpolatedVariable(t *testing.T) {
 		},
 	}
 
-	for i, tc := range cases {
+	for i, test := range tests {
-		actual, err := NewInterpolatedVariable(tc.Input)
+		t.Run(test.Input, func(t *testing.T) {
-		if err != nil != tc.Error {
+			got, err := NewInterpolatedVariable(test.Input)
-			t.Fatalf("%d. Error: %s", i, err)
+			if err != nil != test.Error {
+				t.Errorf("%d. Error: %s", i, err)
 			}
-		if !reflect.DeepEqual(actual, tc.Result) {
+			if !test.Error && !reflect.DeepEqual(got, test.Want) {
-			t.Fatalf("%d bad: %#v", i, actual)
+				t.Errorf(
+					"wrong result\ninput: %s\ngot:   %#v\nwant:  %#v",
+					test.Input, got, test.Want,
+				)
 			}
+		})
 	}
 }