go/importer: use correct path when checking if package was already imported

The importer uses a global (shared) package map across multiple imports
to determine if a package was imported before. That package map is usually
indexed by package (import) path ('id' in this code). However, the binary
importer was using the incoming (possibly unclean) path.

Fixes #15517.

Change-Id: I0c32a708dfccf345e0353fbda20ad882121e437c
Reviewed-on: https://go-review.googlesource.com/23012
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/go/internal/gcimporter/bimport.go

@@ -170,7 +170,7 @@ func (p *importer) declare(obj types.Object) {
 		// imported.
 		// (See also the comment in cmd/compile/internal/gc/bimport.go importer.obj,
 		// switch case importing functions).
-		panic(fmt.Sprintf("%s already declared", alt.Name()))
+		panic(fmt.Sprintf("inconsistent import:\n\t%v\npreviously imported as:\n\t%v\n", alt, obj))
 	}
 }
 

src/go/internal/gcimporter/gcimporter.go

@@ -163,7 +163,7 @@ func Import(packages map[string]*types.Package, path, srcDir string) (pkg *types
 		var data []byte
 		data, err = ioutil.ReadAll(buf)
 		if err == nil {
-			_, pkg, err = BImportData(packages, data, path)
+			_, pkg, err = BImportData(packages, data, id)
 			return
 		}
 	default:

src/go/internal/gcimporter/gcimporter_test.go

@@ -361,3 +361,42 @@ func TestIssue13898(t *testing.T) {
 		t.Fatalf("found %v; want go/types", m.Pkg())
 	}
 }
+
+func TestIssue15517(t *testing.T) {
+	skipSpecialPlatforms(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+		return
+	}
+
+	// On windows, we have to set the -D option for the compiler to avoid having a drive
+	// letter and an illegal ':' in the import path - just skip it (see also issue #3483).
+	if runtime.GOOS == "windows" {
+		t.Skip("avoid dealing with relative paths/drive letters on windows")
+	}
+
+	if f := compile(t, "testdata", "p.go"); f != "" {
+		defer os.Remove(f)
+	}
+
+	// Multiple imports of p must succeed without redeclaration errors.
+	// We use an import path that's not cleaned up so that the eventual
+	// file path for the package is different from the package path; this
+	// will expose the error if it is present.
+	//
+	// (Issue: Both the textual and the binary importer used the file path
+	// of the package to be imported as key into the shared packages map.
+	// However, the binary importer then used the package path to identify
+	// the imported package to mark it as complete; effectively marking the
+	// wrong package as complete. By using an "unclean" package path, the
+	// file and package path are different, exposing the problem if present.
+	// 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 {
+			t.Fatal(err)
+		}
+	}
+}

src/go/internal/gcimporter/testdata/p.go

@@ -0,0 +1,13 @@
+// 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.
+
+// Input for TestIssue15517
+
+package p
+
+const C = 0
+
+var V int
+
+func F() {}