1 files changed, 50 insertions, 6 deletions

diff --git a/libgo/go/os/exec/exec.go b/libgo/go/os/exec/exec.go
index 4680036fddc..a70ed0d20cb 100644
--- a/libgo/go/os/exec/exec.go
+++ b/libgo/go/os/exec/exec.go
@@ -13,7 +13,9 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strconv"
+	"strings"
 	"sync"
 	"syscall"
 )
@@ -237,13 +239,51 @@ func (c *Cmd) Run() error {
 	return c.Wait()
 }
 
+// lookExtensions finds windows executable by its dir and path.
+// It uses LookPath to try appropriate extensions.
+// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
+func lookExtensions(path, dir string) (string, error) {
+	if filepath.Base(path) == path {
+		path = filepath.Join(".", path)
+	}
+	if dir == "" {
+		return LookPath(path)
+	}
+	if filepath.VolumeName(path) != "" {
+		return LookPath(path)
+	}
+	if len(path) > 1 && os.IsPathSeparator(path[0]) {
+		return LookPath(path)
+	}
+	dirandpath := filepath.Join(dir, path)
+	// We assume that LookPath will only add file extension.
+	lp, err := LookPath(dirandpath)
+	if err != nil {
+		return "", err
+	}
+	ext := strings.TrimPrefix(lp, dirandpath)
+	return path + ext, nil
+}
+
 // Start starts the specified command but does not wait for it to complete.
+//
+// The Wait method will return the exit code and release associated resources
+// once the command exits.
 func (c *Cmd) Start() error {
 	if c.lookPathErr != nil {
 		c.closeDescriptors(c.closeAfterStart)
 		c.closeDescriptors(c.closeAfterWait)
 		return c.lookPathErr
 	}
+	if runtime.GOOS == "windows" {
+		lp, err := lookExtensions(c.Path, c.Dir)
+		if err != nil {
+			c.closeDescriptors(c.closeAfterStart)
+			c.closeDescriptors(c.closeAfterWait)
+			return err
+		}
+		c.Path = lp
+	}
 	if c.Process != nil {
 		return errors.New("exec: already started")
 	}
@@ -304,6 +344,8 @@ func (e *ExitError) Error() string {
 // If the command fails to run or doesn't complete successfully, the
 // error is of type *ExitError. Other error types may be
 // returned for I/O problems.
+//
+// Wait releases any resources associated with the Cmd.
 func (c *Cmd) Wait() error {
 	if c.Process == nil {
 		return errors.New("exec: not started")
@@ -387,15 +429,17 @@ func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
 type closeOnce struct {
 	*os.File
 
-	close    sync.Once
-	closeErr error
+	once sync.Once
+	err  error
 }
 
 func (c *closeOnce) Close() error {
-	c.close.Do(func() {
-		c.closeErr = c.File.Close()
-	})
-	return c.closeErr
+	c.once.Do(c.close)
+	return c.err
+}
+
+func (c *closeOnce) close() {
+	c.err = c.File.Close()
 }
 
 // StdoutPipe returns a pipe that will be connected to the command's