[dev.typealias] cmd/doc: update for type alias

For #18130.

Change-Id: I06b05a2b45a2aa6764053fc51e05883063572dad
Reviewed-on: https://go-review.googlesource.com/35670
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/doc/doc_test.go

@@ -71,6 +71,7 @@ var tests = []test{
 			`const MultiLineConst = ...`,                                   // Multi line constant.
 			`var MultiLineVar = map\[struct{ ... }\]struct{ ... }{ ... }`,  // Multi line variable.
 			`func MultiLineFunc\(x interface{ ... }\) \(r struct{ ... }\)`, // Multi line function.
+			`type T1 = T2`, // Type alias
 		},
 		[]string{
 			`const internalConstant = 2`,        // No internal constants.
@@ -89,6 +90,7 @@ var tests = []test{
 			`unexportedTypedConstant`,           // No unexported typed constant.
 			`Field`,                             // No fields.
 			`Method`,                            // No methods.
+			`type T1 T2`, // Type alias does not display as type declaration.
 		},
 	},
 	// Package dump -u
@@ -265,6 +267,18 @@ var tests = []test{
 			`error`,                          // No embedded error.
 		},
 	},
+	// Type T1 dump (alias).
+	{
+		"type T1",
+		[]string{p+".T1"},
+		[]string{
+			`type T1 = T2`,
+		},
+		[]string{
+			`type T1 T2`,
+			`type ExportedType`,
+		},
+	},
 	// Type -u with unexported fields.
 	{
 		"type with unexported fields and -u",

src/cmd/doc/pkg.go

@@ -258,7 +258,11 @@ func (pkg *Package) oneLineNodeDepth(node ast.Node, depth int) string {
 		return fmt.Sprintf("func %s%s%s", recv, name, fnc)
 
 	case *ast.TypeSpec:
-		return fmt.Sprintf("type %s %s", n.Name.Name, pkg.oneLineNodeDepth(n.Type, depth))
+		sep := " "
+		if n.Assign.IsValid() {
+			sep = " = "
+		}
+		return fmt.Sprintf("type %s%s%s", n.Name.Name, sep, pkg.oneLineNodeDepth(n.Type, depth))
 
 	case *ast.FuncType:
 		var params []string

src/cmd/doc/testdata/pkg.go

@@ -172,3 +172,7 @@ const (
 )
 
 const ConstGroup4 ExportedType = ExportedType{}
+
+type T2 int
+
+type T1 = T2