Decode into non-nil pointer's existing value.

Slight adaptation of Ian Remmler <[email protected]>'s fix in pr hashicorp#39:

> If decoding into a pointer, and the pointer points to a value, decode
> into the exitsing value.  Otherwise, decode into a new value and point
> to it.
> Addresses issue hashicorp#38.

decoder.go

@@ -404,6 +404,11 @@ func (d *decoder) decodeMap(name string, node ast.Node, result reflect.Value) er
 }
 
 func (d *decoder) decodePtr(name string, node ast.Node, result reflect.Value) error {
+ // if pointer is not nil, decode into existing value
+ if !result.IsNil() {
+ return d.decode(name, node, result.Elem())
+ }
+
  // Create an element of the concrete (non pointer) type and decode
  // into that. Then set the value of the pointer to this type.
  resultType := result.Type()

decoder_test.go

@@ -616,6 +616,35 @@ func TestDecode_structurePtr(t *testing.T) {
  }
 }
 
+func TestDecode_nonNilStructurePtr(t *testing.T) {
+ type V struct {
+ Key int
+ Foo string
+ DontChange string
+ }
+
+ actual := &V{
+ Key: 42,
+ Foo: "foo",
+ DontChange: "don't change me",
+ }
+
+ err := Decode(&actual, testReadFile(t, "flat.hcl"))
+ if err != nil {
+ t.Fatalf("err: %s", err)
+ }
+
+ expected := &V{
+ Key: 7,
+ Foo: "bar",
+ DontChange: "don't change me",
+ }
+
+ if !reflect.DeepEqual(actual, expected) {
+ t.Fatalf("Actual: %#v\n\nExpected: %#v", actual, expected)
+ }
+}
+
 func TestDecode_structureArray(t *testing.T) {
  // This test is extracted from a failure in Consul (consul.io),
  // hence the interesting structure naming.