cmd/cgo: given typedef struct S T, make C.T and C.struct_S interchangeable

For incomplete struct S, C.T and C.struct_S were interchangeable in Go 1.2
and earlier, because all incomplete types were interchangeable
(even C.struct_S1 and C.struct_S2).

CL 76450043, which fixed issue 7409, made different incomplete types
different from Go's point of view, so that they were no longer completely
interchangeable.

However, imprecision about C.T and C.struct_S - really the same
underlying C type - is the one behavior enabled by the bug that
is most likely to be depended on by existing cgo code.
Explicitly allow it, to keep that code working.

Fixes issue 7786.

LGTM=iant, r
R=golang-codereviews, iant, r
CC=golang-codereviews
https://codereview.appspot.com/98580046

1 files changed, 51 insertions, 0 deletions

diff --git a/misc/cgo/test/issue7786.go b/misc/cgo/test/issue7786.go
new file mode 100644
index 000000000..b92763789
--- /dev/null
+++ b/misc/cgo/test/issue7786.go
@@ -0,0 +1,51 @@
+// Copyright 2013 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 7786. No runtime test, just make sure that typedef and struct/union/class are interchangeable at compile time.
+
+package cgotest
+
+// struct test7786;
+// typedef struct test7786 typedef_test7786;
+// void f7786(struct test7786 *ctx) {}
+// void g7786(typedef_test7786 *ctx) {}
+//
+// typedef struct body7786 typedef_body7786;
+// struct body7786 { int x; };
+// void b7786(struct body7786 *ctx) {}
+// void c7786(typedef_body7786 *ctx) {}
+//
+// typedef union union7786 typedef_union7786;
+// void u7786(union union7786 *ctx) {}
+// void v7786(typedef_union7786 *ctx) {}
+import "C"
+
+func f() {
+	var x1 *C.typedef_test7786
+	var x2 *C.struct_test7786
+	x1 = x2
+	x2 = x1
+	C.f7786(x1)
+	C.f7786(x2)
+	C.g7786(x1)
+	C.g7786(x2)
+
+	var b1 *C.typedef_body7786
+	var b2 *C.struct_body7786
+	b1 = b2
+	b2 = b1
+	C.b7786(b1)
+	C.b7786(b2)
+	C.c7786(b1)
+	C.c7786(b2)
+
+	var u1 *C.typedef_union7786
+	var u2 *C.union_union7786
+	u1 = u2
+	u2 = u1
+	C.u7786(u1)
+	C.u7786(u2)
+	C.v7786(u1)
+	C.v7786(u2)
+}