go/doc: recursively inspect selector expressions

Also adds a couple of simple tests for doc.Examples.

Fixes #4561.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/7067048

src/pkg/go/doc/example.go

@@ -148,13 +148,13 @@ func playExample(file *ast.File, body *ast.BlockStmt) *ast.File {
 	// Find unresolved identifiers and uses of top-level declarations.
 	unresolved := make(map[string]bool)
 	usesTopDecl := false
-	ast.Inspect(body, func(n ast.Node) bool {
-		// For an expression like fmt.Println, only add "fmt" to the
-		// set of unresolved names.
+	var inspectFunc func(ast.Node) bool
+	inspectFunc = func(n ast.Node) bool {
+		// For selector expressions, only inspect the left hand side.
+		// (For an expression like fmt.Println, only add "fmt" to the
+		// set of unresolved names, not "Println".)
 		if e, ok := n.(*ast.SelectorExpr); ok {
-			if id, ok := e.X.(*ast.Ident); ok && id.Obj == nil {
-				unresolved[id.Name] = true
-			}
+			ast.Inspect(e.X, inspectFunc)
 			return false
 		}
 		if id, ok := n.(*ast.Ident); ok {
@@ -165,7 +165,8 @@ func playExample(file *ast.File, body *ast.BlockStmt) *ast.File {
 			}
 		}
 		return true
-	})
+	}
+	ast.Inspect(body, inspectFunc)
 	if usesTopDecl {
 		// We don't support examples that are not self-contained (yet).
 		return nil

src/pkg/go/doc/example_test.go

+// Copyright 2013 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 doc_test
+
+import (
+	"bytes"
+	"go/doc"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"strings"
+	"testing"
+)
+
+const exampleTestFile = `
+package foo_test
+
+import (
+	"fmt"
+	"log"
+	"os/exec"
+)
+
+func ExampleHello() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
+
+func ExampleImport() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+`
+
+var exampleTestCases = []struct {
+	Name, Play, Output string
+}{
+	{
+		Name:   "Hello",
+		Play:   exampleHelloPlay,
+		Output: "Hello, world!\n",
+	},
+	{
+		Name: "Import",
+		Play: exampleImportPlay,
+	},
+}
+
+const exampleHelloPlay = `package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+`
+const exampleImportPlay = `package main
+
+import (
+	"fmt"
+	"log"
+	"os/exec"
+)
+
+func main() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+`
+
+func TestExamples(t *testing.T) {
+	fs := token.NewFileSet()
+	file, err := parser.ParseFile(fs, "test.go", strings.NewReader(exampleTestFile), parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i, e := range doc.Examples(file) {
+		c := exampleTestCases[i]
+		if e.Name != c.Name {
+			t.Errorf("got Name == %q, want %q", e.Name, c.Name)
+		}
+		if w := c.Play; w != "" {
+			var g string // hah
+			if e.Play == nil {
+				g = "<nil>"
+			} else {
+				b := new(bytes.Buffer)
+				if err := format.Node(b, fs, e.Play); err != nil {
+					t.Fatal(err)
+				}
+				g = b.String()
+			}
+			if g != w {
+				t.Errorf("%s: got Play == %q, want %q", c.Name, g, w)
+			}
+		}
+		if g, w := e.Output, c.Output; g != w {
+			t.Errorf("%s: got Output == %q, want %q", c.Name, g, w)
+		}
+	}
+}