From 969b9d8127c0ef3bbffeb1fa7d13a7ec1afccce4 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Daniel=20Mart=C3=AD?= Date: Sun, 26 Aug 2018 06:24:33 -0600 Subject: [PATCH] encoding/json: fix handling of nil anonymous structs MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Given the following types: type S2 struct{ Field string } type S struct{ *S2 } Marshalling a value of type T1 should result in "{}", as there's no way to access any value of T2.Field. This is how Go 1.10 and earlier versions behave. However, in the recent refactor golang.org/cl/125417 I broke this logic. When the encoder found an anonymous struct pointer field that was nil, it no longer skipped the embedded fields underneath it. This can be seen in the added test: --- FAIL: TestAnonymousFields/EmbeddedFieldBehindNilPointer (0.00s) encode_test.go:430: Marshal() = "{\"Field\":\"\\u003c*json.S2 Value\\u003e\"}", want "{}" The human error was a misplaced label, meaning we weren't actually skipping the right loop iteration. Fix that. Change-Id: Iba8a4a77d358dac73dcba4018498fe4f81afa263 Reviewed-on: https://go-review.googlesource.com/131376 Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot Reviewed-by: Brad Fitzpatrick --- src/encoding/json/encode.go | 2 +- src/encoding/json/encode_test.go | 13 +++++++++++++ 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go index 7e5e209b4f..f10124e67d 100644 --- a/src/encoding/json/encode.go +++ b/src/encoding/json/encode.go @@ -629,12 +629,12 @@ type structEncoder struct { func (se structEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) { next := byte('{') +FieldLoop: for i := range se.fields { f := &se.fields[i] // Find the nested struct field by following f.index. fv := v - FieldLoop: for _, i := range f.index { if fv.Kind() == reflect.Ptr { if fv.IsNil() { diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go index 1b7838c895..cd5eadf3c1 100644 --- a/src/encoding/json/encode_test.go +++ b/src/encoding/json/encode_test.go @@ -405,6 +405,19 @@ func TestAnonymousFields(t *testing.T) { return S{s1{1, 2, s2{3, 4}}, 6} }, want: `{"MyInt1":1,"MyInt2":3}`, + }, { + // If an anonymous struct pointer field is nil, we should ignore + // the embedded fields behind it. Not properly doing so may + // result in the wrong output or reflect panics. + label: "EmbeddedFieldBehindNilPointer", + makeInput: func() interface{} { + type ( + S2 struct{ Field string } + S struct{ *S2 } + ) + return S{} + }, + want: `{}`, }} for _, tt := range tests { -- 2.48.1