cmd/cgo: treat simple C typedefs as go aliases

Fixes #21809

Change-Id: Ic43077c6bea3c7cdc9611e74abf07b6deab70433
Reviewed-on: https://go-review.googlesource.com/62670
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/test/cgo_test.go

@@ -82,5 +82,6 @@ func Test20266(t *testing.T)                 { test20266(t) }
 func Test20129(t *testing.T)                 { test20129(t) }
 func Test20910(t *testing.T)                 { test20910(t) }
 func Test21708(t *testing.T)                 { test21708(t) }
+func Test21809(t *testing.T)                 { test21809(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }

misc/cgo/test/issue21809.go

@@ -0,0 +1,45 @@
+// Copyright 2017 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 cgotest
+
+// Issue 21809.  Compile C `typedef` to go type aliases.
+
+// typedef long MySigned_t;
+// /* tests alias-to-alias */
+// typedef MySigned_t MySigned2_t;
+//
+// long takes_long(long x) { return x * x; }
+// MySigned_t takes_typedef(MySigned_t x) { return x * x; }
+import "C"
+
+import "testing"
+
+func test21809(t *testing.T) {
+    longVar := C.long(3)
+    typedefVar := C.MySigned_t(4)
+    typedefTypedefVar := C.MySigned2_t(5)
+
+    // all three should be considered identical to `long`
+    if ret := C.takes_long(longVar); ret != 9 {
+        t.Errorf("got %v but expected %v", ret, 9)
+    }
+    if ret := C.takes_long(typedefVar); ret != 16 {
+        t.Errorf("got %v but expected %v", ret, 16)
+    }
+    if ret := C.takes_long(typedefTypedefVar); ret != 25 {
+        t.Errorf("got %v but expected %v", ret, 25)
+    }
+
+    // They should also be identical to the typedef'd type
+    if ret := C.takes_typedef(longVar); ret != 9 {
+        t.Errorf("got %v but expected %v", ret, 9)
+    }
+    if ret := C.takes_typedef(typedefVar); ret != 16 {
+        t.Errorf("got %v but expected %v", ret, 16)
+    }
+    if ret := C.takes_typedef(typedefTypedefVar); ret != 25 {
+        t.Errorf("got %v but expected %v", ret, 25)
+    }
+}

src/cmd/cgo/out.go

@@ -110,7 +110,13 @@ func (p *Package) writeDefs() {
 		// Which is not useful. Moreover we never override source info,
 		// so subsequent source code uses the same source info.
 		// Moreover, empty file name makes compile emit no source debug info at all.
-		noSourceConf.Fprint(fgo2, fset, def.Go)
+		var buf bytes.Buffer
+		noSourceConf.Fprint(&buf, fset, def.Go)
+		if bytes.HasPrefix(buf.Bytes(), []byte("_Ctype_")) {
+			// This typedef is of the form `typedef a b` and should be an alias.
+			fmt.Fprintf(fgo2, "= ")
+		}
+		fmt.Fprintf(fgo2, "%s", buf.Bytes())
 		fmt.Fprintf(fgo2, "\n\n")
 	}
 	if *gccgo {