From 2d357d8da864fc8d14e7e7834d521aa638243772 Mon Sep 17 00:00:00 2001
From: LE Manh Cuong <cuong.manhle.vn@gmail.com>
Date: Thu, 16 May 2019 02:28:47 +0700
Subject: [PATCH] cmd/compile: fix typecheck type alias makes wrong export
 symbol metadata

typecheck type alias always replaces the original definition of the symbol.
This is wrong behavior because if the symbol's definition is replaced by a
local type alias, it ends up being written to compiled file as an alias,
instead of the original type.

To fix, only replace the definition of symbol with global type alias.

Fixes #31959

Change-Id: Id85a15e8a9d6a4b06727e655a95dc81e63df633a
Reviewed-on: https://go-review.googlesource.com/c/go/+/177378
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
---
 src/cmd/compile/internal/gc/typecheck.go |  6 +++++-
 test/fixedbugs/issue31959.dir/a.go       | 12 ++++++++++++
 test/fixedbugs/issue31959.dir/main.go    | 21 +++++++++++++++++++++
 test/fixedbugs/issue31959.go             |  7 +++++++
 test/fixedbugs/issue31959.out            |  2 ++
 5 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue31959.dir/a.go
 create mode 100644 test/fixedbugs/issue31959.dir/main.go
 create mode 100644 test/fixedbugs/issue31959.go
 create mode 100644 test/fixedbugs/issue31959.out

diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 81f59013f4ef02..4cb28d6100b149 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -3671,7 +3671,11 @@ func typecheckdef(n *Node) {
 					n.SetDiag(true)
 					goto ret
 				}
-				n.Sym.Def = asTypesNode(p.Ntype)
+				// For package-level type aliases, set n.Sym.Def so we can identify
+				// it as a type alias during export. See also #31959.
+				if n.Name.Curfn == nil {
+					n.Sym.Def = asTypesNode(p.Ntype)
+				}
 			}
 			break
 		}
diff --git a/test/fixedbugs/issue31959.dir/a.go b/test/fixedbugs/issue31959.dir/a.go
new file mode 100644
index 00000000000000..6c7ffa38c12b82
--- /dev/null
+++ b/test/fixedbugs/issue31959.dir/a.go
@@ -0,0 +1,12 @@
+// 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.
+
+package a
+
+type T struct{}
+
+func F() {
+	type T = int
+	println(T(0))
+}
diff --git a/test/fixedbugs/issue31959.dir/main.go b/test/fixedbugs/issue31959.dir/main.go
new file mode 100644
index 00000000000000..895c4e5345773e
--- /dev/null
+++ b/test/fixedbugs/issue31959.dir/main.go
@@ -0,0 +1,21 @@
+// run
+
+// 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.
+
+// Check import package contains type alias in function
+// with the same name with an export type not panic
+
+package main
+
+import (
+	"fmt"
+
+	"a"
+)
+
+func main() {
+	fmt.Println(a.T{})
+	a.F()
+}
diff --git a/test/fixedbugs/issue31959.go b/test/fixedbugs/issue31959.go
new file mode 100644
index 00000000000000..af6f1341729458
--- /dev/null
+++ b/test/fixedbugs/issue31959.go
@@ -0,0 +1,7 @@
+// rundir
+
+// 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.
+
+package ignored
diff --git a/test/fixedbugs/issue31959.out b/test/fixedbugs/issue31959.out
new file mode 100644
index 00000000000000..8ddcb67af1c72e
--- /dev/null
+++ b/test/fixedbugs/issue31959.out
@@ -0,0 +1,2 @@
+{}
+0