[dev.typealias] go/internal/gccgoimporter: support for type aliases

For #18130.

Change-Id: Iac182a6c5bc62633eb02191d9da6166d3b254c4c
Reviewed-on: https://go-review.googlesource.com/35268
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/internal/gccgoimporter/importer_test.go

@@ -101,6 +101,7 @@ var importerTests = [...]importerTest{
 	{pkgpath: "unicode", name: "IsUpper", want: "func IsUpper(r rune) bool"},
 	{pkgpath: "unicode", name: "MaxRune", want: "const MaxRune untyped rune", wantval: "1114111"},
 	{pkgpath: "imports", wantinits: []string{"imports..import", "fmt..import", "math..import"}},
+	{pkgpath: "alias", name: "IntAlias2", want: "type IntAlias2 = Int"},
 }
 
 func TestGoxImporter(t *testing.T) {

src/go/internal/gccgoimporter/parser.go

@@ -370,27 +370,41 @@ func (p *parser) parseConst(pkg *types.Package) *types.Const {
 	return types.NewConst(token.NoPos, pkg, name, typ, val)
 }
 
-// TypeName = ExportedName .
-func (p *parser) parseTypeName() *types.TypeName {
-	pkg, name := p.parseExportedName()
-	scope := pkg.Scope()
-	if obj := scope.Lookup(name); obj != nil {
-		return obj.(*types.TypeName)
-	}
-	obj := types.NewTypeName(token.NoPos, pkg, name, nil)
-	// a named type may be referred to before the underlying type
-	// is known - set it up
-	types.NewNamed(obj, nil, nil)
-	scope.Insert(obj)
-	return obj
-}
-
-// NamedType = TypeName Type { Method } .
+// NamedType = TypeName [ "=" ] Type { Method } .
+// TypeName  = ExportedName .
 // Method    = "func" "(" Param ")" Name ParamList ResultList ";" .
 func (p *parser) parseNamedType(n int) types.Type {
-	obj := p.parseTypeName()
+	pkg, name := p.parseExportedName()
+	scope := pkg.Scope()
+
+	if p.tok == '=' {
+		// type alias
+		p.next()
+		typ := p.parseType(pkg)
+		if obj := scope.Lookup(name); obj != nil {
+			typ = obj.Type() // use previously imported type
+			if typ == nil {
+				p.errorf("%v (type alias) used in cycle", obj)
+			}
+		} else {
+			obj = types.NewTypeName(token.NoPos, pkg, name, typ)
+			scope.Insert(obj)
+		}
+		p.typeMap[n] = typ
+		return typ
+	}
+
+	// named type
+	obj := scope.Lookup(name)
+	if obj == nil {
+		// a named type may be referred to before the underlying type
+		// is known - set it up
+		tname := types.NewTypeName(token.NoPos, pkg, name, nil)
+		types.NewNamed(tname, nil, nil)
+		scope.Insert(tname)
+		obj = tname
+	}
 
-	pkg := obj.Pkg()
 	typ := obj.Type()
 	p.typeMap[n] = typ
 
@@ -409,8 +423,8 @@ func (p *parser) parseNamedType(n int) types.Type {
 		nt.SetUnderlying(underlying.Underlying())
 	}
 
+	// collect associated methods
 	for p.tok == scanner.Ident {
-		// collect associated methods
 		p.expectKeyword("func")
 		p.expect('(')
 		receiver, _ := p.parseParam(pkg)

src/go/internal/gccgoimporter/testdata/alias.gox

@@ -0,0 +1,4 @@
+v1;
+package alias;
+pkgpath alias;
+type <type 115 "I1" <type 116 interface { M1 (? <type 117 "IntAlias2" = <type 118 "IntAlias" = <type 119 "Int" <type -11>>>>) < type 114>; M2 () <type 1>; }>>;