go/doc: add more test cases

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5571043

src/pkg/go/doc/testdata/c.go

+// Copyright 2012 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 c
+
+import "a"
+
+// ----------------------------------------------------------------------------
+// Test that empty declarations don't cause problems
+
+const ()
+
+type ()
+
+var ()
+
+// ----------------------------------------------------------------------------
+// Test that types with documentation on both, the Decl and the Spec node
+// are handled correctly.
+
+// A (should see this)
+type A struct{}
+
+// B (should see this)
+type (
+	B struct{}
+)
+
+type (
+	// C (should see this)
+	C struct{}
+)
+
+// D (should not see this)
+type (
+	// D (should see this)
+	D struct{}
+)
+
+// E (should see this for E2 and E3)
+type (
+	// E1 (should see this)
+	E1 struct{}
+	E2 struct{}
+	E3 struct{}
+	// E4 (should see this)
+	E4 struct{}
+)
+
+// ----------------------------------------------------------------------------
+// Test that local and imported types are different when
+// handling anonymous fields.
+
+type T1 struct{}
+
+func (t1 *T1) M() {}
+
+// T2 must not show methods of local T1
+type T2 struct {
+	a.T1 // not the same as locally declared T1
+}

src/pkg/go/doc/testdata/c.out

+// 
+PACKAGE c
+
+IMPORTPATH
+	testdata/c
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/c.go
+
+TYPES
+	// A (should see this) 
+	type A struct{}
+
+	// B (should see this) 
+	type B struct{}
+
+	// C (should see this) 
+	type C struct{}
+
+	// D (should see this) 
+	type D struct{}
+
+	// E1 (should see this) 
+	type E1 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E2 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E3 struct{}
+
+	// E4 (should see this) 
+	type E4 struct{}
+
+	// 
+	type T1 struct{}
+
+	// 
+	func (t1 *T1) M()
+
+	// T2 must not show methods of local T1 
+	type T2 struct {
+		a.T1	// not the same as locally declared T1
+	}
+