go/internal/gcimporter: update gcimporter.go to incorporate std lib changes

This CL brings over changes from https://golang.org/cl/74354/
which were not brought over.

The code was adjusted slightly such that a filename is still available
for ImportData even if a custom lookup function is provided (adjustments
are on lines 133, 188-193).

Change-Id: I58960e648c9aae1683eb4d7f8d7578f09349eca2
Reviewed-on: https://go-review.googlesource.com/c/143017
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

go/internal/gcimporter/gcimporter.go

@@ -128,14 +128,33 @@ func ImportData(packages map[string]*types.Package, filename, id string, data io
 // the corresponding package object to the packages map, and returns the object.
 // The packages map must contain all packages already imported.
 //
-func Import(packages map[string]*types.Package, path, srcDir string) (pkg *types.Package, err error) {
+func Import(packages map[string]*types.Package, path, srcDir string, lookup func(path string) (io.ReadCloser, error)) (pkg *types.Package, err error) {
-	filename, id := FindPkg(path, srcDir)
+	var rc io.ReadCloser
+	var filename, id string
+	if lookup != nil {
+		// With custom lookup specified, assume that caller has
+		// converted path to a canonical import path for use in the map.
+		if path == "unsafe" {
+			return types.Unsafe, nil
+		}
+		id = path
+
+		// No need to re-import if the package was imported completely before.
+		if pkg = packages[id]; pkg != nil && pkg.Complete() {
+			return
+		}
+		f, err := lookup(path)
+		if err != nil {
+			return nil, err
+		}
+		rc = f
+	} else {
+		filename, id = FindPkg(path, srcDir)
 		if filename == "" {
 			if path == "unsafe" {
 				return types.Unsafe, nil
 			}
-		err = fmt.Errorf("can't find import: %q", id)
+			return nil, fmt.Errorf("can't find import: %q", id)
-		return
 		}
 
 		// no need to re-import if the package was imported completely before
@@ -146,24 +165,32 @@ func Import(packages map[string]*types.Package, path, srcDir string) (pkg *types
 		// open file
 		f, err := os.Open(filename)
 		if err != nil {
-		return
+			return nil, err
 		}
 		defer func() {
-		f.Close()
 			if err != nil {
 				// add file name to error
-			err = fmt.Errorf("reading export data: %s: %v", filename, err)
+				err = fmt.Errorf("%s: %v", filename, err)
 			}
 		}()
+		rc = f
+	}
+	defer rc.Close()
 
 	var hdr string
-	buf := bufio.NewReader(f)
+	buf := bufio.NewReader(rc)
 	if hdr, err = FindExportData(buf); err != nil {
 		return
 	}
 
 	switch hdr {
 	case "$$\n":
+		// Work-around if we don't have a filename; happens only if lookup != nil.
+		// Either way, the filename is only needed for importer error messages, so
+		// this is fine.
+		if filename == "" {
+			filename = path
+		}
 		return ImportData(packages, filename, id, buf)
 
 	case "$$B\n":

go/internal/gcimporter/gcimporter11_test.go

@@ -54,7 +54,7 @@ func TestImportedTypes(t *testing.T) {
 		importPath := s[0]
 		objName := s[1]
 
-		pkg, err := Import(make(map[string]*types.Package), importPath, ".")
+		pkg, err := Import(make(map[string]*types.Package), importPath, ".", nil)
 		if err != nil {
 			t.Error(err)
 			continue

go/internal/gcimporter/gcimporter_test.go

@@ -88,7 +88,7 @@ func compile(t *testing.T, dirname, filename string) string {
 
 func testPath(t *testing.T, path, srcDir string) *types.Package {
 	t0 := time.Now()
-	pkg, err := Import(make(map[string]*types.Package), path, srcDir)
+	pkg, err := Import(make(map[string]*types.Package), path, srcDir, nil)
 	if err != nil {
 		t.Errorf("testPath(%s): %s", path, err)
 		return nil
@@ -190,7 +190,7 @@ func TestVersionHandling(t *testing.T) {
 		}
 
 		// test that export data can be imported
-		_, err := Import(make(map[string]*types.Package), pkgpath, dir)
+		_, err := Import(make(map[string]*types.Package), pkgpath, dir, nil)
 		if err != nil {
 			// ok to fail if it fails with a newer version error for select files
 			if strings.Contains(err.Error(), "newer version") {
@@ -227,7 +227,7 @@ func TestVersionHandling(t *testing.T) {
 		defer os.Remove(filename)
 
 		// test that importing the corrupted file results in an error
-		_, err = Import(make(map[string]*types.Package), pkgpath, dir)
+		_, err = Import(make(map[string]*types.Package), pkgpath, dir, nil)
 		if err == nil {
 			t.Errorf("import corrupted %q succeeded", pkgpath)
 		} else if msg := err.Error(); !strings.Contains(msg, "version skew") {
@@ -290,7 +290,7 @@ func TestCorrectMethodPackage(t *testing.T) {
 	}
 
 	imports := make(map[string]*types.Package)
-	_, err := Import(imports, "net/http", ".")
+	_, err := Import(imports, "net/http", ".", nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -346,7 +346,7 @@ func TestIssue13898(t *testing.T) {
 
 	// import go/internal/gcimporter which imports go/types partially
 	imports := make(map[string]*types.Package)
-	_, err := Import(imports, "go/internal/gcimporter", ".")
+	_, err := Import(imports, "go/internal/gcimporter", ".", nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -414,7 +414,7 @@ func TestIssue15517(t *testing.T) {
 	// The same issue occurs with vendoring.)
 	imports := make(map[string]*types.Package)
 	for i := 0; i < 3; i++ {
-		if _, err := Import(imports, "./././testdata/p", "."); err != nil {
+		if _, err := Import(imports, "./././testdata/p", ".", nil); err != nil {
 			t.Fatal(err)
 		}
 	}
@@ -468,7 +468,7 @@ func TestIssue20046(t *testing.T) {
 }
 
 func importPkg(t *testing.T, path string) *types.Package {
-	pkg, err := Import(make(map[string]*types.Package), path, ".")
+	pkg, err := Import(make(map[string]*types.Package), path, ".", nil)
 	if err != nil {
 		t.Fatal(err)
 	}