config: parse TerraformVariables

config/interpolate.go

@@ -84,6 +84,13 @@ type SimpleVariable struct {
 	Key string
 }
 
+// TerraformVariable is a "terraform."-prefixed variable used to access
+// metadata about the Terraform run.
+type TerraformVariable struct {
+	Field string
+	key   string
+}
+
 // A UserVariable is a variable that is referencing a user variable
 // that is inputted from outside the configuration. This looks like
 // "${var.foo}"
@@ -101,6 +108,8 @@ func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
 		return NewPathVariable(v)
 	} else if strings.HasPrefix(v, "self.") {
 		return NewSelfVariable(v)
+	} else if strings.HasPrefix(v, "terraform.") {
+		return NewTerraformVariable(v)
 	} else if strings.HasPrefix(v, "var.") {
 		return NewUserVariable(v)
 	} else if strings.HasPrefix(v, "module.") {
@@ -278,6 +287,22 @@ func (v *SimpleVariable) GoString() string {
 	return fmt.Sprintf("*%#v", *v)
 }
 
+func NewTerraformVariable(key string) (*TerraformVariable, error) {
+	field := key[len("terraform."):]
+	return &TerraformVariable{
+		Field: field,
+		key:   key,
+	}, nil
+}
+
+func (v *TerraformVariable) FullKey() string {
+	return v.key
+}
+
+func (v *TerraformVariable) GoString() string {
+	return fmt.Sprintf("*%#v", *v)
+}
+
 func NewUserVariable(key string) (*UserVariable, error) {
 	name := key[len("var."):]
 	elem := ""

config/interpolate_test.go

@@ -63,6 +63,14 @@ func TestNewInterpolatedVariable(t *testing.T) {
 			},
 			false,
 		},
+		{
+			"terraform.env",
+			&TerraformVariable{
+				Field: "env",
+				key:   "terraform.env",
+			},
+			false,
+		},
 	}
 
 	for i, tc := range cases {