go/gcimporter15: support export/import of invalid aliases

+ test

Tested on 1.6, 1.7, and 1.8.

Fixes golang/go#17731.

Change-Id: I06dff4a72ff08ed5e8ae1d23a1e65fe719c03180
Reviewed-on: https://go-review.googlesource.com/32581
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

go/gcimporter15/bexport.go

@@ -177,24 +177,6 @@ func (p *exporter) pkg(pkg *types.Package, emptypath bool) {
 }
 
 func (p *exporter) obj(obj types.Object) {
-	if orig := original(obj); orig != obj {
-		if orig == nil {
-			// invalid alias - don't export for now (issue 17731)
-			return
-		}
-
-		if !p.reexported[orig] {
-			p.obj(orig)
-			p.reexported[orig] = true
-		}
-
-		p.tag(aliasTag)
-		p.pos(obj)
-		p.string(obj.Name())
-		p.qualifiedName(orig)
-		return
-	}
-
 	switch obj := obj.(type) {
 	case *types.Const:
 		p.tag(constTag)
@@ -221,6 +203,20 @@ func (p *exporter) obj(obj types.Object) {
 		p.paramList(sig.Params(), sig.Variadic())
 		p.paramList(sig.Results(), false)
 
+	case *types_Alias:
+		// make sure the original is exported before the alias
+		// (if the alias declaration was invalid, orig will be nil)
+		orig := original(obj)
+		if orig != nil && !p.reexported[orig] {
+			p.obj(orig)
+			p.reexported[orig] = true
+		}
+
+		p.tag(aliasTag)
+		p.pos(obj)
+		p.string(obj.Name())
+		p.qualifiedName(orig)
+
 	default:
 		log.Fatalf("gcimporter: unexpected object %v (%T)", obj, obj)
 	}
@@ -280,6 +276,10 @@ func commonPrefixLen(a, b string) int {
 }
 
 func (p *exporter) qualifiedName(obj types.Object) {
+	if obj == nil {
+		p.string("")
+		return
+	}
 	p.string(obj.Name())
 	p.pkg(obj.Pkg(), false)
 }

go/gcimporter15/bexport18_test.go

@@ -0,0 +1,59 @@
+// 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.
+
+// +build go1.8
+
+package gcimporter_test
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"testing"
+
+	gcimporter "golang.org/x/tools/go/gcimporter15"
+)
+
+func TestInvalidAlias(t *testing.T) {
+	// parse and typecheck
+	const src = "package p; func InvalidAlias => foo.f"
+	fset1 := token.NewFileSet()
+	f, err := parser.ParseFile(fset1, "p.go", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var conf types.Config
+	pkg, err := conf.Check("p", fset1, []*ast.File{f}, nil)
+	if err == nil {
+		t.Fatal("invalid source type-checked without error")
+	}
+	if pkg == nil {
+		t.Fatal("nil package returned")
+	}
+
+	// export
+	exportdata := gcimporter.BExportData(fset1, pkg)
+
+	// import
+	imports := make(map[string]*types.Package)
+	fset2 := token.NewFileSet()
+	_, pkg2, err := gcimporter.BImportData(fset2, imports, exportdata, pkg.Path())
+	if err != nil {
+		t.Fatalf("BImportData(%s): %v", pkg.Path(), err)
+	}
+
+	// pkg2 must contain InvalidAlias as an invalid Alias
+	obj := pkg2.Scope().Lookup("InvalidAlias")
+	if obj == nil {
+		t.Fatal("InvalidAlias not found")
+	}
+	alias, ok := obj.(*types.Alias)
+	if !ok {
+		t.Fatalf("got %v; want alias", alias)
+	}
+	if alias.Type() != types.Typ[types.Invalid] || alias.Orig() != nil {
+		t.Fatalf("got %v (orig = %v); want invalid alias", alias, alias.Orig())
+	}
+}

go/gcimporter15/bimport.go

@@ -282,11 +282,13 @@ func (p *importer) obj(tag int) {
 		p.declare(types.NewFunc(pos, pkg, name, sig))
 
 	case aliasTag:
-		aliasPos := p.pos()
-		aliasName := p.string()
-		pkg, name := p.qualifiedName()
-		obj := pkg.Scope().Lookup(name)
-		p.declare(newAlias(aliasPos, p.pkgList[0], aliasName,obj))
+		pos := p.pos()
+		name := p.string()
+		var orig types.Object
+		if pkg, name := p.qualifiedName(); pkg != nil {
+			orig = pkg.Scope().Lookup(name)
+		}
+		p.declare(types_NewAlias(pos, p.pkgList[0], name, orig))
 
 	default:
 		errorf("unexpected object tag %d", tag)
@@ -347,7 +349,9 @@ var (
 
 func (p *importer) qualifiedName() (pkg *types.Package, name string) {
 	name = p.string()
-	pkg = p.pkg()
+	if name != "" {
+		pkg = p.pkg()
+	}
 	return
 }
 

go/gcimporter15/newalias16.go

@@ -11,13 +11,18 @@ import (
 	"go/types"
 )
 
-func newAlias(pos token.Pos, pkg *types.Package, name string, orig types.Object) types.Object {
-	errorf("unexpected alias in non-Go1.8 export data: %s.%s => %v", pkg.Name(), name, orig)
+type types_Alias struct {
+	types.Object
+	dummy int
+} // satisfies types.Object but will never be encountered
+
+func types_NewAlias(pos token.Pos, pkg *types.Package, name string, orig types.Object) types.Object {
+	errorf("unexpected alias in non-Go1.8 export data: %s.%s => %v", pkg.Name(), name, orig) // panics
 	panic("unreachable")
 }
 
-func original(obj types.Object) types.Object {
-	return obj // don't know about aliases
+func original(types.Object) types.Object {
+	panic("unreachable")
 }
 
 const testfile = "exports17.go"

go/gcimporter15/newalias18.go

@@ -8,7 +8,9 @@ package gcimporter
 
 import "go/types"
 
-func newAlias => types.NewAlias
+type types_Alias => types.Alias
+
+func types_NewAlias => types.NewAlias
 
 // TODO(gri) Consider exporting this functionality from go/types (issue 17730).
 func original(obj types.Object) types.Object {