go/internal/gcimporter: use empty string for the top-level package path

I made a mistake with the initial port of iexport.go in that I left the
original package path of the top-level package in the export data.
The package path for the top-level package should have been empty so
that it can be changed when the package is loaded.

Updates golang/go#28260

Change-Id: I781e63317a54eaf59385f25d18609e73ff97d572
Reviewed-on: https://go-review.googlesource.com/c/tools/+/201097
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: stamblerre

go/internal/gcimporter/iexport.go

@@ -26,7 +26,10 @@ import (
 const iexportVersion = 0
 
 // IExportData returns the binary export data for pkg.
+//
 // If no file set is provided, position info will be missing.
+// The package path of the top-level package will not be recorded,
+// so that calls to IImportData can override with a provided package path.
 func IExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error) {
 	defer func() {
 		if e := recover(); e != nil {
@@ -46,6 +49,7 @@ func IExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error)
 		stringIndex: map[string]uint64{},
 		declIndex:   map[types.Object]uint64{},
 		typIndex:    map[types.Type]uint64{},
+		localpkg:    pkg,
 	}
 
 	for i, pt := range predeclared() {
@@ -71,7 +75,7 @@ func IExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error)
 	// Append indices to data0 section.
 	dataLen := uint64(p.data0.Len())
 	w := p.newWriter()
-	w.writeIndex(p.declIndex, pkg)
+	w.writeIndex(p.declIndex)
 	w.flush()
 
 	// Assemble header.
@@ -93,14 +97,14 @@ func IExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error)
 // we're writing out the main index, which is also read by
 // non-compiler tools and includes a complete package description
 // (i.e., name and height).
-func (w *exportWriter) writeIndex(index map[types.Object]uint64, localpkg *types.Package) {
+func (w *exportWriter) writeIndex(index map[types.Object]uint64) {
 	// Build a map from packages to objects from that package.
 	pkgObjs := map[*types.Package][]types.Object{}
 
 	// For the main index, make sure to include every package that
 	// we reference, even if we're not exporting (or reexporting)
 	// any symbols from it.
-	pkgObjs[localpkg] = nil
+	pkgObjs[w.p.localpkg] = nil
 	for pkg := range w.p.allPkgs {
 		pkgObjs[pkg] = nil
 	}
@@ -119,12 +123,12 @@ func (w *exportWriter) writeIndex(index map[types.Object]uint64, localpkg *types
 	}
 
 	sort.Slice(pkgs, func(i, j int) bool {
-		return pkgs[i].Path() < pkgs[j].Path()
+		return w.exportPath(pkgs[i]) < w.exportPath(pkgs[j])
 	})
 
 	w.uint64(uint64(len(pkgs)))
 	for _, pkg := range pkgs {
-		w.string(pkg.Path())
+		w.string(w.exportPath(pkg))
 		w.string(pkg.Name())
 		w.uint64(uint64(0)) // package height is not needed for go/types
 
@@ -141,6 +145,8 @@ type iexporter struct {
 	fset *token.FileSet
 	out  *bytes.Buffer
 
+	localpkg *types.Package
+
 	// allPkgs tracks all packages that have been referenced by
 	// the export data, so we can ensure to include them in the
 	// main index.
@@ -193,6 +199,13 @@ type exportWriter struct {
 	prevLine int64
 }
 
+func (w *exportWriter) exportPath(pkg *types.Package) string {
+	if pkg == w.p.localpkg {
+		return ""
+	}
+	return pkg.Path()
+}
+
 func (p *iexporter) doDecl(obj types.Object) {
 	w := p.newWriter()
 	w.setPkg(obj.Pkg(), false)
@@ -302,7 +315,7 @@ func (w *exportWriter) pkg(pkg *types.Package) {
 	// Ensure any referenced packages are declared in the main index.
 	w.p.allPkgs[pkg] = true
 
-	w.string(pkg.Path())
+	w.string(w.exportPath(pkg))
 }
 
 func (w *exportWriter) qualifiedIdent(obj types.Object) {

go/internal/gcimporter/iimport.go

@@ -147,24 +147,14 @@ func IImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 		errorf("no packages found for %s", path)
 		panic("unreachable")
 	}
-	var localpkg *types.Package
-	for _, pkg := range pkgList {
-		if pkg.Path() == path {
-			localpkg = pkg
-			break
-		}
-	}
-	if localpkg == nil {
-		localpkg = pkgList[0]
-	}
-
-	names := make([]string, 0, len(p.pkgIndex[localpkg]))
-	for name := range p.pkgIndex[localpkg] {
+	p.ipkg = pkgList[0]
+	names := make([]string, 0, len(p.pkgIndex[p.ipkg]))
+	for name := range p.pkgIndex[p.ipkg] {
 		names = append(names, name)
 	}
 	sort.Strings(names)
 	for _, name := range names {
-		p.doDecl(localpkg, name)
+		p.doDecl(p.ipkg, name)
 	}
 
 	for _, typ := range p.interfaceList {
@@ -174,17 +164,18 @@ func IImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 	// record all referenced packages as imports
 	list := append(([]*types.Package)(nil), pkgList[1:]...)
 	sort.Sort(byPath(list))
-	localpkg.SetImports(list)
+	p.ipkg.SetImports(list)
 
 	// package was imported completely and without errors
-	localpkg.MarkComplete()
+	p.ipkg.MarkComplete()
 
 	consumed, _ := r.Seek(0, io.SeekCurrent)
-	return int(consumed), localpkg, nil
+	return int(consumed), p.ipkg, nil
 }
 
 type iimporter struct {
 	ipath   string
+	ipkg    *types.Package
 	version int
 
 	stringData  []byte
@@ -236,6 +227,9 @@ func (p *iimporter) pkgAt(off uint64) *types.Package {
 		return pkg
 	}
 	path := p.stringAt(off)
+	if path == p.ipath {
+		return p.ipkg
+	}
 	errorf("missing package %q in %q", path, p.ipath)
 	return nil
 }