go/importer: added go/importer package, adjusted go/types

- The go/importer package provides access to compiler-specific importers.
- Adjusted go/internal/gcimporter and go/types as needed.
- types.Check was removed - not much simpler than calling types.Config.Check.
- Package "unsafe" is now handled by the type checker; importers are not
  called for it anymore.
- In std lib tests, re-use importer for faster testing
  (no need to re-import previously imported packages).
- Minor cleanups.

The code still needs cleanups before submitting.

Change-Id: Idd456da2e9641688fe056504367348926feb0755
Reviewed-on: https://go-review.googlesource.com/8767
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/cmd/api/goapi_test.go b/src/cmd/api/goapi_test.go
index 00c45c3bcd..6184e14477 100644
--- a/src/cmd/api/goapi_test.go
+++ b/src/cmd/api/goapi_test.go
@@ -39,7 +39,8 @@ func TestGolden(t *testing.T) {
 		// TODO(gri) remove extra pkg directory eventually
 		goldenFile := filepath.Join("testdata", "src", "pkg", fi.Name(), "golden.txt")
 		w := NewWalker(nil, "testdata/src/pkg")
-		w.export(w.Import(fi.Name()))
+		pkg, _ := w.Import(fi.Name())
+		w.export(pkg)
 
 		if *updateGolden {
 			os.Remove(goldenFile)
@@ -178,7 +179,8 @@ func BenchmarkAll(b *testing.B) {
 			w := NewWalker(context, filepath.Join(build.Default.GOROOT, "src"))
 			for _, name := range pkgNames {
 				if name != "unsafe" && !strings.HasPrefix(name, "cmd/") {
-					w.export(w.Import(name))
+					pkg, _ := w.Import(name)
+					w.export(pkg)
 				}
 			}
 			w.Features()