t.Skip("skipping in short mode")
	}

	testenv.MustHaveGoBuild(t)

	// Collect non-test files.
	dirFiles := make(map[string][]string)
	root := filepath.Join(testenv.GOROOT(t), "src")
	walkPkgDirs(root, func(dir string, filenames []string) {
		dirFiles[dir] = filenames
	}, t.Error)

	c := &stdlibChecker{
		dirFiles: dirFiles,
		pkgs:     make(map[string]*futurePackage),
	}

	start := time.Now()