go/doc: don't drop "factory" functions with dot-imported result types

Fixes #13742.

Change-Id: I7c8b51b60e31402bf708bf8d70e07fd06295e8ce
Reviewed-on: https://go-review.googlesource.com/18393Reviewed-by: Russ Cox <rsc@golang.org>

src/go/doc/reader.go

@@ -152,6 +152,7 @@ type reader struct {
 
 	// declarations
 	imports   map[string]int
+	hasDotImp bool     // if set, package contains a dot import
 	values    []*Value // consts and vars
 	types     map[string]*namedType
 	funcs     methodSet
@@ -471,6 +472,9 @@ func (r *reader) readFile(src *ast.File) {
 					if s, ok := spec.(*ast.ImportSpec); ok {
 						if import_, err := strconv.Unquote(s.Path.Value); err == nil {
 							r.imports[import_] = 1
+							if s.Name != nil && s.Name.Name == "." {
+								r.hasDotImp = true
+							}
 						}
 					}
 				}
@@ -641,11 +645,12 @@ 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] || t.isEmbedded && visible) {
+		if t.decl == nil && (predeclaredTypes[t.name] || 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): move any associated values, funcs, and methods
-			// back to the top-level so that they are not lost.
+			// the AST is incomplete), or we have a dot-import (and all bets are off):
+			// move any associated values, funcs, and methods back to the top-level so
+			// that they are not lost.
 			// 1) move values
 			r.values = append(r.values, t.values...)
 			// 2) move factory functions

src/go/doc/testdata/issue13742.0.golden

+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+

src/go/doc/testdata/issue13742.1.golden

+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+

src/go/doc/testdata/issue13742.2.golden

+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+

src/go/doc/testdata/issue13742.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 issue13742
+
+import (
+	"go/ast"
+	. "go/ast"
+)
+
+// Both F0 and G0 should appear as functions.
+func F0(Node)  {}
+func G0() Node { return nil }
+
+// Both F1 and G1 should appear as functions.
+func F1(ast.Node)  {}
+func G1() ast.Node { return nil }