plumbing: fix pack commands for the file client on Windows

The default git install on Windows doesn't come with separate commands
for receive-pack and upload-pack.

Author: strib

plumbing/transport/file/client.go

@@ -40,11 +40,7 @@ func (r *runner) Command(cmd string, ep transport.Endpoint, auth transport.AuthM
 		cmd = r.ReceivePackBin
 	}
 
-	if _, err := exec.LookPath(cmd); err != nil {
-		return nil, err
-	}
-
-	return &command{cmd: exec.Command(cmd, ep.Path())}, nil
+	return makeCommand(cmd, ep)
 }
 
 type command struct {

plumbing/transport/file/client_cmd_unix.go

@@ -0,0 +1,18 @@
+// +build !windows
+
+package file
+
+import (
+	"os/exec"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+	"gopkg.in/src-d/go-git.v4/plumbing/transport/internal/common"
+)
+
+func makeCommand(cmd string, ep transport.Endpoint) (common.Command, error) {
+	if _, err := exec.LookPath(cmd); err != nil {
+		return nil, err
+	}
+
+	return &command{cmd: exec.Command(cmd, ep.Path())}, nil
+}

plumbing/transport/file/client_cmd_windows.go

@@ -0,0 +1,29 @@
+// +build windows
+
+package file
+
+import (
+	"os/exec"
+	"strings"
+
+	"gopkg.in/src-d/go-git.v4/plumbing/transport"
+	"gopkg.in/src-d/go-git.v4/plumbing/transport/internal/common"
+)
+
+// In the default Windows git install, there is no separate
+// git-upload-pack or git-receive-pack binaries; we must use "git
+// upload-pack" and "git receive-pack" instead.
+func makeCommand(cmd string, ep transport.Endpoint) (common.Command, error) {
+	var subcommands []string
+	if strings.HasPrefix(cmd, "git-") {
+		subcommands = strings.SplitN(cmd, "-", 2)
+		cmd = subcommands[0]
+	}
+
+	if _, err := exec.LookPath(cmd); err != nil {
+		return nil, err
+	}
+
+	return &command{cmd: exec.Command(
+		cmd, append(subcommands[1:], ep.Path())...)}, nil
+}