go/doc: hide methods on locally-declared predeclared types

Currently if you declare a type overwriting a predeclared type
and export methods on it they will be exposed in godoc, even
though the type itself is not exported. This corrects that
by making all methods on these types hidden, since that's
the expected output.

Fixes #9860

Change-Id: I14037bdcef1b4bbefcf299a143bac8bf363718e0
Reviewed-on: https://go-review.googlesource.com/20610Reviewed-by: Russ Cox <rsc@golang.org>

src/go/doc/reader.go

@@ -645,7 +645,9 @@ func (r *reader) computeMethodSets() {
 func (r *reader) cleanupTypes() {
 	for _, t := range r.types {
 		visible := r.isVisible(t.name)
-		if t.decl == nil && (predeclaredTypes[t.name] || visible && (t.isEmbedded || r.hasDotImp)) {
+		predeclared := predeclaredTypes[t.name]
+
+		if t.decl == nil && (predeclared || visible && (t.isEmbedded || r.hasDotImp)) {
 			// t.name is a predeclared type (and was not redeclared in this package),
 			// or it was embedded somewhere but its declaration is missing (because
 			// the AST is incomplete), or we have a dot-import (and all bets are off):
@@ -660,6 +662,7 @@ func (r *reader) cleanupTypes() {
 				r.funcs[name] = f
 			}
 			// 3) move methods
+			if !predeclared {
 				for name, m := range t.methods {
 					// don't overwrite functions with the same name - drop them
 					if _, found := r.funcs[name]; !found {
@@ -667,6 +670,7 @@ func (r *reader) cleanupTypes() {
 					}
 				}
 			}
+		}
 		// remove types w/o declaration or which are not visible
 		if t.decl == nil || !visible {
 			delete(r.types, t.name)

src/go/doc/testdata/predeclared.0.golden

+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go

src/go/doc/testdata/predeclared.1.golden

+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go
+
+TYPES
+	// 
+	type bool int
+
+	// Must not be visible. 
+	func (b bool) String() string
+
+	// 
+	type error struct{}
+
+	// Must not be visible. 
+	func (e error) Error() string
+

src/go/doc/testdata/predeclared.2.golden

+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go

src/go/doc/testdata/predeclared.go

+// Copyright 2016 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 predeclared is a go/doc test for handling of
+// exported methods on locally-defined predeclared types.
+// See issue 9860.
+package predeclared
+
+type error struct{}
+
+// Must not be visible.
+func (e error) Error() string {
+	return ""
+}
+
+type bool int
+
+// Must not be visible.
+func (b bool) String() string {
+	return ""
+}