cmd/cgo: for -godefs, promote first field of anonymous union

Update issue 6677

When a struct contains an anonymous union, use the type and
name of the first field in the union.

This should make the glibc <sys/resource.h> file work; in that
file struct rusage has fields like

__extension__ union
{
        long int ru_maxrss;
        __syscall_slong_t __ru_maxrss_word;
};

in which the field that matters is ru_maxrss and
__ru_maxrss_word just exists to advance to the next field on
systems where the kernel uses long long fields but userspace
expects long fields.

LGTM=mikioh.mikioh
R=golang-codereviews, mikioh.mikioh
CC=golang-codereviews
https://codereview.appspot.com/106260044

3 files changed, 58 insertions, 0 deletions

diff --git a/misc/cgo/testgodefs/anonunion.go b/misc/cgo/testgodefs/anonunion.go
new file mode 100644
index 000000000..7bc736b9d
--- /dev/null
+++ b/misc/cgo/testgodefs/anonunion.go
@@ -0,0 +1,26 @@
+// 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.
+//
+// +build ignore
+
+package main
+
+// This file tests that when cgo -godefs sees a struct with a field
+// that is an anonymous union, the first field in the union is
+// promoted to become a field of the struct.  See issue 6677 for
+// background.
+
+/*
+typedef struct {
+	union {
+		long l;
+		int c;
+	};
+} t;
+*/
+import "C"
+
+// Input for cgo -godefs.
+
+type T C.t
diff --git a/misc/cgo/testgodefs/main.go b/misc/cgo/testgodefs/main.go
new file mode 100644
index 000000000..eaf91bc11
--- /dev/null
+++ b/misc/cgo/testgodefs/main.go
@@ -0,0 +1,12 @@
+// 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
+
+// Test that the struct field in anonunion.go was promoted.
+var v1 T
+var v2 = v1.L
+
+func main() {
+}
diff --git a/misc/cgo/testgodefs/test.bash b/misc/cgo/testgodefs/test.bash
new file mode 100755
index 000000000..cfbeae7dc
--- /dev/null
+++ b/misc/cgo/testgodefs/test.bash
@@ -0,0 +1,20 @@
+# 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.
+
+# We are testing cgo -godefs, which translates Go files that use
+# import "C" into Go files with Go definitions of types defined in the
+# import "C" block.  Add more tests here.
+FILE_PREFIXES="anonunion"
+
+RM=
+for FP in $FILE_PREFIXES
+do
+  go tool cgo -godefs ${FP}.go > ${FP}_defs.go
+  RM="${RM} ${FP}_defs.go"
+done
+
+go build . && ./testgodefs
+EXIT=$?
+rm -rf _obj testgodefs ${RM}
+exit $EXIT