From 5fc55b31803e9929d104ce58a4dcbef97a87a83e Mon Sep 17 00:00:00 2001
From: LE Manh Cuong <cuong.manhle.vn@gmail.com>
Date: Sat, 30 Mar 2019 03:16:44 +0700
Subject: [PATCH] cmd/compile: use FmtLeft to generate symbol name for
 unexported interface methods

The bug in 29612 is that there are two similar-looking anonymous interface
types in two different packages, ./p1/ssa and ./p2/ssa:

v.(interface{ foo() }).foo()

These types should be treated differently because the unexported method
makes the types different (according to the spec).

But when generating the type descriptors for those two types, they
both have the name "interface { ssa.foo() }". They thus get the same
symbol, and the linker happily unifies them. It picks an arbitrary one
for the runtime to use, but that breaks conversions from concrete types
that have a foo method from the package which had its interface type
overwritten.

We need to encode the metadata symbol for unexported methods as package
path qualified (The same as we did in CL 27791 for struct fields).

So switching from FmtUnsigned to Fmtleft by default fixes the issue.
In case of generating namedata, FmtUnsigned is used.

The benchmark result ends up in no significant change of compiled binary
compare to the immediate parent.

Fixes #29612

Change-Id: I775aff91ae4a1bb16eb18a48d55e3b606f3f3352
Reviewed-on: https://go-review.googlesource.com/c/go/+/170157
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
---
 src/cmd/compile/internal/gc/fmt.go          |  6 ++++-
 test/fixedbugs/issue29612.dir/main.go       | 24 ++++++++++++++++++
 test/fixedbugs/issue29612.dir/p1/ssa/ssa.go | 18 +++++++++++++
 test/fixedbugs/issue29612.dir/p2/ssa/ssa.go | 28 +++++++++++++++++++++
 4 files changed, 75 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue29612.dir/main.go
 create mode 100644 test/fixedbugs/issue29612.dir/p1/ssa/ssa.go
 create mode 100644 test/fixedbugs/issue29612.dir/p2/ssa/ssa.go

diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index 12f341b660..67b521feed 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -752,7 +752,11 @@ func typefmt(t *types.Type, flag FmtFlag, mode fmtMode, depth int) string {
 			case types.IsExported(f.Sym.Name):
 				buf = append(buf, sconv(f.Sym, FmtShort, mode)...)
 			default:
-				buf = append(buf, sconv(f.Sym, FmtUnsigned, mode)...)
+				flag1 := FmtLeft
+				if flag&FmtUnsigned != 0 {
+					flag1 = FmtUnsigned
+				}
+				buf = append(buf, sconv(f.Sym, flag1, mode)...)
 			}
 			buf = append(buf, tconv(f.Type, FmtShort, mode, depth)...)
 		}
diff --git a/test/fixedbugs/issue29612.dir/main.go b/test/fixedbugs/issue29612.dir/main.go
new file mode 100644
index 0000000000..9dbc4c4cd9
--- /dev/null
+++ b/test/fixedbugs/issue29612.dir/main.go
@@ -0,0 +1,24 @@
+// 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.
+
+// Do not panic on conversion to anonymous interface, which
+// is similar-looking interface types in different packages.
+
+package main
+
+import (
+	ssa1 "./p1/ssa"
+	ssa2 "./p2/ssa"
+)
+
+func main() {
+	v1 := &ssa1.T{}
+	_ = v1
+
+	v2 := &ssa2.T{}
+	ssa2.Works(v2)
+	ssa2.Panics(v2) // This call must not panic
+}
diff --git a/test/fixedbugs/issue29612.dir/p1/ssa/ssa.go b/test/fixedbugs/issue29612.dir/p1/ssa/ssa.go
new file mode 100644
index 0000000000..8f6eb97f8f
--- /dev/null
+++ b/test/fixedbugs/issue29612.dir/p1/ssa/ssa.go
@@ -0,0 +1,18 @@
+// 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 ssa
+
+type T struct{}
+
+func (T) foo() {}
+
+type fooer interface {
+	foo()
+}
+
+func Unused(v interface{}) {
+	v.(fooer).foo()
+	v.(interface{ foo() }).foo()
+}
diff --git a/test/fixedbugs/issue29612.dir/p2/ssa/ssa.go b/test/fixedbugs/issue29612.dir/p2/ssa/ssa.go
new file mode 100644
index 0000000000..df57314b8c
--- /dev/null
+++ b/test/fixedbugs/issue29612.dir/p2/ssa/ssa.go
@@ -0,0 +1,28 @@
+// 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 ssa
+
+type T struct{}
+
+func (T) foo() {}
+
+type fooer interface {
+	foo()
+}
+
+func Works(v interface{}) {
+	switch v.(type) {
+	case interface{}:
+		v.(fooer).foo()
+	}
+}
+
+func Panics(v interface{}) {
+	switch v.(type) {
+	case interface{}:
+		v.(fooer).foo()
+		v.(interface{ foo() }).foo()
+	}
+}
-- 
2.50.0