cmd/cgo: enforce typing of 0-sized types

cgo represents all 0-sized and unsized types internally as [0]byte. This means that pointers to incomplete types would be interchangable, even if given a name by typedef.

Fixes #7409.

LGTM=iant
R=golang-codereviews, bradfitz, iant
CC=golang-codereviews
https://golang.org/cl/76450043

2 files changed, 19 insertions, 0 deletions

diff --git a/misc/cgo/errors/err3.go b/misc/cgo/errors/err3.go
new file mode 100644
index 0000000000..3680a4a4c1
--- /dev/null
+++ b/misc/cgo/errors/err3.go
@@ -0,0 +1,18 @@
+// Copyright 2014 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 main
+
+/*
+typedef struct foo foo_t;
+typedef struct bar bar_t;
+
+foo_t *foop;
+*/
+import "C"
+
+func main() {
+	x := (*C.bar_t)(nil)
+	C.foop = x // ERROR HERE
+}
diff --git a/misc/cgo/errors/test.bash b/misc/cgo/errors/test.bash
index 697ae2fed2..f0f60c8445 100755
--- a/misc/cgo/errors/test.bash
+++ b/misc/cgo/errors/test.bash
@@ -26,6 +26,7 @@ check() {
 
 check err1.go
 check err2.go
+check err3.go
 
 rm -rf errs _obj
 exit 0