cmd/cgo: use type aliases for #define type macros

Cgo's initial design for handling "#define foo int*" involved
rewriting "C.foo" to "*_Ctype_int" everywhere. But now that we have
type aliases, we can declare "type _Ctype_foo = *_Ctype_int" once, and
then rewrite "C.foo" to just "_Ctype_foo".

This is important for go/types's UsesCgo mode, where go/types needs to
be able to figure out a type for each C.foo identifier using only the
information written into _cgo_gotypes.go.

Fixes #38649.

Change-Id: Ia0f8c2d82df81efb1be5bc26195ea9154c0af871
Reviewed-on: https://go-review.googlesource.com/c/go/+/230037
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 27 insertions, 0 deletions

diff --git a/misc/cgo/test/test.go b/misc/cgo/test/test.go
index b0148995fe..b5009d43ce 100644
--- a/misc/cgo/test/test.go
+++ b/misc/cgo/test/test.go
@@ -897,6 +897,10 @@ static uint16_t issue31093F(uint16_t v) { return v; }
 
 // issue 32579
 typedef struct S32579 { unsigned char data[1]; } S32579;
+
+// issue 38649
+// Test that #define'd type aliases work.
+#define netbsd_gid unsigned int
 */
 import "C"
 
@@ -2192,3 +2196,7 @@ func test32579(t *testing.T) {
 		t.Errorf("&s[0].data[0] failed: got %d, want %d", s[0].data[0], 1)
 	}
 }
+
+// issue 38649
+
+var issue38649 C.netbsd_gid = 42
diff --git a/misc/cgo/testgodefs/testdata/issue38649.go b/misc/cgo/testgodefs/testdata/issue38649.go
new file mode 100644
index 0000000000..6af74d6058
--- /dev/null
+++ b/misc/cgo/testgodefs/testdata/issue38649.go
@@ -0,0 +1,15 @@
+// Copyright 2020 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.
+//
+// +build ignore
+
+package main
+
+/*
+struct Issue38649 { int x; };
+#define issue38649 struct Issue38649
+*/
+import "C"
+
+type issue38649 C.issue38649
diff --git a/misc/cgo/testgodefs/testdata/main.go b/misc/cgo/testgodefs/testdata/main.go
index ef45b95e65..2e1ad3376a 100644
--- a/misc/cgo/testgodefs/testdata/main.go
+++ b/misc/cgo/testgodefs/testdata/main.go
@@ -19,5 +19,8 @@ var v6 = B{}
 // Test that S is fully defined
 var v7 = S{}
 
+// Test that #define'd type is fully defined
+var _ = issue38649{X: 0}
+
 func main() {
 }
diff --git a/misc/cgo/testgodefs/testgodefs_test.go b/misc/cgo/testgodefs/testgodefs_test.go
index 438d23d65c..178fff3fbc 100644
--- a/misc/cgo/testgodefs/testgodefs_test.go
+++ b/misc/cgo/testgodefs/testgodefs_test.go
@@ -23,6 +23,7 @@ var filePrefixes = []string{
 	"fieldtypedef",
 	"issue37479",
 	"issue37621",
+	"issue38649",
 }
 
 func TestGoDefs(t *testing.T) {