cmd/fix: don't depend on *GetTypeID functions being present

cgo uses the presence of these functions to determine whether
a given type is in the CFTypeRef hierarchy and thus should be
a uintptr instead of a pointer. But if the *GetTypeID functions
aren't used by the user code, then they won't be present in the
cgo output, and thus cmd/fix won't see them.

Use the simpler rule that anything ending in *Ref should be
rewritten. This could over-rewrite, but I don't see a simpler
solution. Unlike cgo, it is easy to edit the output to fix any
issues. And fix is a much rarer operation than cgo.

This is a revert of portions of CL 87616.

Update #23091

Change-Id: I74ecd9fb25490a3d279b372e107248452bb62185
Reviewed-on: https://go-review.googlesource.com/88075
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/fix/cftype.go

@@ -30,19 +30,17 @@ var cftypeFix = fix{
 // and similar for other *Ref types.
 // This fix finds nils initializing these types and replaces the nils with 0s.
 func cftypefix(f *ast.File) bool {
-	var tc TypeConfig
-	return typefix(f, &tc, func(s string) bool {
-		return strings.HasPrefix(s, "C.") && strings.HasSuffix(s, "Ref") &&
-			(s == "C.CFTypeRef" || tc.External[s[:len(s)-3]+"GetTypeID"] == "func() C.CFTypeID")
+	return typefix(f, func(s string) bool {
+		return strings.HasPrefix(s, "C.") && strings.HasSuffix(s, "Ref") && s != "C.CFAllocatorRef"
 	})
 }
 
 // typefix replaces nil with 0 for all nils whose type, when passed to badType, returns true.
-func typefix(f *ast.File, tc *TypeConfig, badType func(string) bool) bool {
+func typefix(f *ast.File, badType func(string) bool) bool {
 	if !imports(f, "C") {
 		return false
 	}
-	typeof, _ := typecheck(tc, f)
+	typeof, _ := typecheck(&TypeConfig{}, f)
 
 	// step 1: Find all the nils with the offending types.
 	// Compute their replacement.

src/cmd/fix/jnitype.go

@@ -27,8 +27,7 @@ var jniFix = fix{
 // and similar for subtypes of jobject.
 // This fix finds nils initializing these types and replaces the nils with 0s.
 func jnifix(f *ast.File) bool {
-	var tc TypeConfig
-	return typefix(f, &tc, func(s string) bool {
+	return typefix(f, func(s string) bool {
 		switch s {
 		case "C.jobject":
 			return true

src/cmd/fix/typecheck.go

@@ -152,6 +152,7 @@ func typecheck(cfg *TypeConfig, f *ast.File) (typeof map[interface{}]string, ass
 
 	// If we import "C", add types of cgo objects.
 	cfg.External = map[string]string{}
+	cfg1.External = cfg.External
 	if imports(f, "C") {
 		// Run cgo on gofmtFile(f)
 		// Parse, extract decls from _cgo_gotypes.go