cmd/cgo: build unique C type cache keys from parent names

When translating C types, cache the in-progress type under its parent
names, so that anonymous structs can also be translated for multiple
typedefs, without clashing.

Standalone types are not affected by this change.

Also updated the test for issue 9026 because the C struct name
generation algorithm has changed.

Fixes #31891

Change-Id: I00cc64852a2617ce33da13f74caec886af05b9f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/181857
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/test/cgo_test.go

@@ -58,6 +58,7 @@ func Test27660(t *testing.T)                 { test27660(t) }
 func Test28896(t *testing.T)                 { test28896(t) }
 func Test30065(t *testing.T)                 { test30065(t) }
 func Test32579(t *testing.T)                 { test32579(t) }
+func Test31891(t *testing.T)                 { test31891(t) }
 func TestAlign(t *testing.T)                 { testAlign(t) }
 func TestAtol(t *testing.T)                  { testAtol(t) }
 func TestBlocking(t *testing.T)              { testBlocking(t) }

misc/cgo/test/issue31891.c

@@ -0,0 +1,13 @@
+// Copyright 2019 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.
+
+#include "_cgo_export.h"
+
+void callIssue31891() {
+    Issue31891A a;
+    useIssue31891A(&a);
+
+    Issue31891B b;
+    useIssue31891B(&b);
+}

misc/cgo/test/testdata/issue9026/issue9026.go

@@ -29,7 +29,7 @@ func Test(t *testing.T) {
 	// Brittle: the assertion may fail spuriously when the algorithm
 	// changes, but should remain stable otherwise.
 	got := fmt.Sprintf("%T %T", in, opts)
-	want := "issue9026._Ctype_struct___0 *issue9026._Ctype_struct___0"
+	want := "issue9026._Ctype_struct___0 *issue9026._Ctype_struct___1"
 	if got != want {
 		t.Errorf("Non-deterministic type names: got %s, want %s", got, want)
 	}

misc/cgo/test/testx.go

@@ -108,6 +108,17 @@ void callMulti(void);
 // issue 28772 part 2 - part 1 in issuex.go
 #define issue28772Constant2 2
 
+
+// issue 31891
+typedef struct {
+	long obj;
+} Issue31891A;
+
+typedef struct {
+	long obj;
+} Issue31891B;
+
+void callIssue31891(void);
 */
 import "C"
 
@@ -517,3 +528,15 @@ func test20910(t *testing.T) {
 // issue 28772 part 2
 
 const issue28772Constant2 = C.issue28772Constant2
+
+// issue 31891
+
+//export useIssue31891A
+func useIssue31891A(c *C.Issue31891A) {}
+
+//export useIssue31891B
+func useIssue31891B(c *C.Issue31891B) {}
+
+func test31891(t *testing.T) {
+	C.callIssue31891()
+}

src/cmd/cgo/gcc.go

@@ -2189,6 +2189,11 @@ func (c *typeConv) FinishType(pos token.Pos) {
 // Type returns a *Type with the same memory layout as
 // dtype when used as the type of a variable or a struct field.
 func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
+	return c.loadType(dtype, pos, "")
+}
+
+// loadType recursively loads the requested dtype and its dependency graph.
+func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Type {
 	// Always recompute bad pointer typedefs, as the set of such
 	// typedefs changes as we see more types.
 	checkCache := true
@@ -2196,7 +2201,9 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 		checkCache = false
 	}
 
-	key := dtype.String()
+	// The cache key should be relative to its parent.
+	// See issue https://golang.org/issue/31891
+	key := parent + " > " + dtype.String()
 
 	if checkCache {
 		if t, ok := c.m[key]; ok {
@@ -2236,7 +2243,7 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 			// Translate to zero-length array instead.
 			count = 0
 		}
-		sub := c.Type(dt.Type, pos)
+		sub := c.loadType(dt.Type, pos, key)
 		t.Align = sub.Align
 		t.Go = &ast.ArrayType{
 			Len: c.intExpr(count),
@@ -2381,7 +2388,7 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 		c.ptrs[key] = append(c.ptrs[key], t)
 
 	case *dwarf.QualType:
-		t1 := c.Type(dt.Type, pos)
+		t1 := c.loadType(dt.Type, pos, key)
 		t.Size = t1.Size
 		t.Align = t1.Align
 		t.Go = t1.Go
@@ -2465,7 +2472,7 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 		}
 		name := c.Ident("_Ctype_" + dt.Name)
 		goIdent[name.Name] = name
-		sub := c.Type(dt.Type, pos)
+		sub := c.loadType(dt.Type, pos, key)
 		if c.badPointerTypedef(dt) {
 			// Treat this typedef as a uintptr.
 			s := *sub