cmd/cgo, misc/cgo: only cache anonymous struct typedefs with parent name

CL 181857 broke the translation of certain C types using cmd/cgo -godefs
because it stores each typedef, array and qualified type with their
parent type name in the translation cache.

Fix this by only considering the parent type for typedefs of anonymous
structs which is the only case where types might become ambiguous.

Updates #31891
Fixes #37479
Fixes #37621

Change-Id: I301a749ec89585789cb0d213593bb8b7341beb88
Reviewed-on: https://go-review.googlesource.com/c/go/+/226341
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/testgodefs/testdata/issue37479.go

@@ -0,0 +1,33 @@
+// 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
+
+/*
+typedef struct A A;
+
+typedef struct {
+	struct A *next;
+	struct A **prev;
+} N;
+
+struct A
+{
+	N n;
+};
+
+typedef struct B
+{
+	A* a;
+} B;
+*/
+import "C"
+
+type N C.N
+
+type A C.A
+
+type B C.B

misc/cgo/testgodefs/testdata/issue37621.go

@@ -0,0 +1,23 @@
+// 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 tt {
+	long long a;
+	long long b;
+};
+
+struct s {
+	struct tt ts[3];
+};
+*/
+import "C"
+
+type TT C.struct_tt
+
+type S C.struct_s

misc/cgo/testgodefs/testdata/main.go

@@ -11,5 +11,13 @@ var v2 = v1.L
 // Test that P, Q, and R all point to byte.
 var v3 = Issue8478{P: (*byte)(nil), Q: (**byte)(nil), R: (***byte)(nil)}
 
+// Test that N, A and B are fully defined
+var v4 = N{}
+var v5 = A{}
+var v6 = B{}
+
+// Test that S is fully defined
+var v7 = S{}
+
 func main() {
 }

misc/cgo/testgodefs/testgodefs_test.go

@@ -21,6 +21,8 @@ var filePrefixes = []string{
 	"anonunion",
 	"issue8478",
 	"fieldtypedef",
+	"issue37479",
+	"issue37621",
 }
 
 func TestGoDefs(t *testing.T) {

src/cmd/cgo/gcc.go

@@ -2243,7 +2243,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 			// Translate to zero-length array instead.
 			count = 0
 		}
-		sub := c.loadType(dt.Type, pos, key)
+		sub := c.Type(dt.Type, pos)
 		t.Align = sub.Align
 		t.Go = &ast.ArrayType{
 			Len: c.intExpr(count),
@@ -2388,7 +2388,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 		c.ptrs[key] = append(c.ptrs[key], t)
 
 	case *dwarf.QualType:
-		t1 := c.loadType(dt.Type, pos, key)
+		t1 := c.Type(dt.Type, pos)
 		t.Size = t1.Size
 		t.Align = t1.Align
 		t.Go = t1.Go
@@ -2472,7 +2472,13 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 		}
 		name := c.Ident("_Ctype_" + dt.Name)
 		goIdent[name.Name] = name
-		sub := c.loadType(dt.Type, pos, key)
+		akey := ""
+		if c.anonymousStructTypedef(dt) {
+			// only load type recursively for typedefs of anonymous
+			// structs, see issues 37479 and 37621.
+			akey = key
+		}
+		sub := c.loadType(dt.Type, pos, akey)
 		if c.badPointerTypedef(dt) {
 			// Treat this typedef as a uintptr.
 			s := *sub
@@ -2993,6 +2999,13 @@ func fieldPrefix(fld []*ast.Field) string {
 	return prefix
 }
 
+// anonymousStructTypedef reports whether dt is a C typedef for an anonymous
+// struct.
+func (c *typeConv) anonymousStructTypedef(dt *dwarf.TypedefType) bool {
+	st, ok := dt.Type.(*dwarf.StructType)
+	return ok && st.StructName == ""
+}
+
 // badPointerTypedef reports whether t is a C typedef that should not be considered a pointer in Go.
 // A typedef is bad if C code sometimes stores non-pointers in this type.
 // TODO: Currently our best solution is to find these manually and list them as