From d5df4d61ce87e6ba9ba0bad06b835e0b100660e7 Mon Sep 17 00:00:00 2001 From: Dominik Honnef Date: Sun, 28 Jul 2019 15:19:43 +0200 Subject: [PATCH] cmd/gofmt: don't turn nil slices into empty slices during rewriting MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The go/ast package uses and guarantees nil slices for optional elements that weren't present in the parsed source code, such as the list of return values of a function. Packages using go/ast rely on this attribute and check for nils explicitly. One such package is go/printer. In the presence of empty slices instead of nil slices, it generates invalid code, such as "case :" instead of "default:". The issues that this CL fixes are all manifestations of that problem, each for a different syntactic element. Fixes #33103 Fixes #33104 Fixes #33105 Change-Id: I219f95a7da820eaf697a4ee227d458ab6e4a80bd Reviewed-on: https://go-review.googlesource.com/c/go/+/187917 Reviewed-by: Daniel Martí Reviewed-by: Robert Griesemer Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot --- src/cmd/gofmt/rewrite.go | 6 ++++++ src/cmd/gofmt/testdata/rewrite10.golden | 19 +++++++++++++++++++ src/cmd/gofmt/testdata/rewrite10.input | 19 +++++++++++++++++++ 3 files changed, 44 insertions(+) create mode 100644 src/cmd/gofmt/testdata/rewrite10.golden create mode 100644 src/cmd/gofmt/testdata/rewrite10.input diff --git a/src/cmd/gofmt/rewrite.go b/src/cmd/gofmt/rewrite.go index 79b7858a5a..bab22e04cd 100644 --- a/src/cmd/gofmt/rewrite.go +++ b/src/cmd/gofmt/rewrite.go @@ -271,6 +271,12 @@ func subst(m map[string]reflect.Value, pattern reflect.Value, pos reflect.Value) // Otherwise copy. switch p := pattern; p.Kind() { case reflect.Slice: + if p.IsNil() { + // Do not turn nil slices into empty slices. go/ast + // guarantees that certain lists will be nil if not + // populated. + return reflect.Zero(p.Type()) + } v := reflect.MakeSlice(p.Type(), p.Len(), p.Len()) for i := 0; i < p.Len(); i++ { v.Index(i).Set(subst(m, p.Index(i), pos)) diff --git a/src/cmd/gofmt/testdata/rewrite10.golden b/src/cmd/gofmt/testdata/rewrite10.golden new file mode 100644 index 0000000000..1dd781fbb0 --- /dev/null +++ b/src/cmd/gofmt/testdata/rewrite10.golden @@ -0,0 +1,19 @@ +//gofmt -r=a->a + +// Copyright 2019 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Issue 33103, 33104, and 33105. + +package pkg + +func fn() { + _ = func() { + switch { + default: + } + } + _ = func() string {} + _ = func() { var ptr *string; println(ptr) } +} diff --git a/src/cmd/gofmt/testdata/rewrite10.input b/src/cmd/gofmt/testdata/rewrite10.input new file mode 100644 index 0000000000..1dd781fbb0 --- /dev/null +++ b/src/cmd/gofmt/testdata/rewrite10.input @@ -0,0 +1,19 @@ +//gofmt -r=a->a + +// Copyright 2019 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Issue 33103, 33104, and 33105. + +package pkg + +func fn() { + _ = func() { + switch { + default: + } + } + _ = func() string {} + _ = func() { var ptr *string; println(ptr) } +} -- 2.50.0