Added test for depfile dependant build (#622)

* Added test for depfile dependant build

* fix error spotted in windows build

cmd/gb/depfile.go

@@ -79,14 +79,16 @@ func fetchIfMissing(root, prefix, version string) {
 		fatalf("unable to construct gzip reader: %v", err)
 	}
 
-	parent, _ := filepath.Split(dest)
+	parent, pkg := filepath.Split(dest)
 	mkdirall(parent)
 	tmpdir := tempdir(parent)
+	defer os.RemoveAll(tmpdir)
+
+	tmpdir = filepath.Join(tmpdir, pkg)
 
 	if err := untar.Untar(tmpdir, gzr); err != nil {
 		fatalf("unable to untar: %v", err)
 	}
-	defer os.RemoveAll(tmpdir)
 
 	dents, err := ioutil.ReadDir(tmpdir)
 	if err != nil {

cmd/gb/depfile_test.go

@@ -1,6 +1,10 @@
 package main_test
 
-import "testing"
+import (
+	"path/filepath"
+	"runtime"
+	"testing"
+)
 
 func TestMissingDepfile(t *testing.T) {
 	gb := T{T: t}
@@ -21,3 +25,38 @@ func main() {
 	gb.runFail("build")
 	gb.grepStderr(`FATAL: command "build" failed:.+import "github.com/a/b": not found`, `import "github.com/a/b": not found`)
 }
+
+func TestDepfileFetchMissing(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test during -short")
+	}
+
+	gb := T{T: t}
+	defer gb.cleanup()
+
+	gb.tempDir("src/github.com/user/proj/a/")
+	gb.tempFile("src/github.com/user/proj/a/main.go", `package main
+
+import "github.com/pkg/profile"
+
+func main() {
+	defer profile.Start().Stop()
+}
+`)
+	gb.tempFile("depfile", `
+github.com/pkg/profile	version=1.1.0
+`)
+
+	gb.cd(gb.tempdir)
+	gbhome := gb.tempDir(".gb")
+	gb.setenv("GB_HOME", gbhome)
+	gb.setenv("DEBUG", ".")
+	gb.run("build")
+	name := "a"
+	if runtime.GOOS == "windows" {
+		name += ".exe"
+	}
+	gb.wantExecutable(gb.path("bin", name), "expected $PROJECT/bin/"+name)
+	gb.grepStdout("^fetching github.com/pkg/profile", "fetching pkg/profile not found")
+	gb.mustExist(filepath.Join(gbhome, "cache", "8fd41ea4fa48cd8435005bad56faeefdc57a25d6", "src", "github.com", "pkg", "profile", "profile.go"))
+}

cmd/gb/internal/untar/untar.go

@@ -13,6 +13,9 @@ import (
 // Untar extracts the contents of r to the destination dest.
 // dest must not aleady exist.
 func Untar(dest string, r io.Reader) error {
+	if exists(dest) {
+		return errors.Errorf("%q must not exist", dest)
+	}
 	parent, _ := filepath.Split(dest)
 	tmpdir, err := ioutil.TempDir(parent, ".untar")
 	if err != nil {
@@ -84,3 +87,8 @@ func writefile(path string, r io.Reader, mode os.FileMode) error {
 	}
 	return w.Close()
 }
+
+func exists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil || !os.IsNotExist(err)
+}