cmd/cgo, debug/dwarf: fix translation of zero-size arrays

In cgo, now that recursive calls to typeConv.Type() always work,
we can more robustly calculate the array sizes based on the size
of our element type.

Also, in debug/dwarf, the decision to call zeroType is made
based on a type's usage	within a particular struct, but dwarf.Type
values are cached in typeCache, so the modification might affect
uses of the type in other structs.  Current compilers don't appear
to share DWARF type entries for "[]foo" and "[0]foo", but they also
don't consistently share type entries in other cases.  Arguably
modifying the types is an improvement in some cases, but varying
translated types according to compiler whims seems like a bad idea.

Lastly, also in debug/dwarf, zeroType only needs to rewrite the
top-level dimension, and only if the rest of the array size is
non-zero.

Fixes issue 8428.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/127980043

Committer: Ian Lance Taylor <iant@golang.org>

1 files changed, 48 insertions, 0 deletions

diff --git a/misc/cgo/test/issue8428.go b/misc/cgo/test/issue8428.go
new file mode 100644
index 000000000..f5b0ee497
--- /dev/null
+++ b/misc/cgo/test/issue8428.go
@@ -0,0 +1,48 @@
+// 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 cgotest
+
+// Issue 8428.  Cgo inconsistently translated zero size arrays.
+
+/*
+struct issue8428one {
+	char b;
+	char rest[];
+};
+
+struct issue8428two {
+	void *p;
+	char b;
+	char rest[0];
+};
+
+struct issue8428three {
+	char w[1][2][3][0];
+	char x[2][3][0][1];
+	char y[3][0][1][2];
+	char z[0][1][2][3];
+};
+*/
+import "C"
+
+import "unsafe"
+
+var _ = C.struct_issue8428one{
+	b:    C.char(0),
+	rest: [0]C.char{},
+}
+
+var _ = C.struct_issue8428two{
+	p:    unsafe.Pointer(nil),
+	b:    C.char(0),
+	rest: [0]C.char{},
+}
+
+var _ = C.struct_issue8428three{
+	w: [1][2][3][0]C.char{},
+	x: [2][3][0][1]C.char{},
+	y: [3][0][1][2]C.char{},
+	z: [0][1][2][3]C.char{},
+}