Allow - for stdout in path mapper (#147)

README.md

@@ -385,8 +385,8 @@ function `NamedMapper(name, mapper)`.
 
 | Name              | Description
 |-------------------|---------------------------------------------------
-| `path`            | A path. ~ expansion is applied.
-| `existingfile`    | An existing file. ~ expansion is applied. `-` is accepted for stdin.
+| `path`            | A path. ~ expansion is applied. `-` is accepted for stdout, and will be passed unaltered.
+| `existingfile`    | An existing file. ~ expansion is applied. `-` is accepted for stdin, and will be passed unaltered.
 | `existingdir`     | An existing directory. ~ expansion is applied.
 | `counter`         | Increment a numeric field. Useful for `-vvv`. Can accept `-s`, `--long` or `--long=N`.
 

mapper.go

@@ -554,7 +554,9 @@ func pathMapper(r *Registry) MapperFunc {
 		if err != nil {
 			return err
 		}
-		path = ExpandPath(path)
+		if path != "-" {
+			path = ExpandPath(path)
+		}
 		target.SetString(path)
 		return nil
 	}

mapper_test.go

@@ -378,3 +378,18 @@ func TestFileMapper(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, os.Stdin, cli.File)
 }
+
+func TestPathMapper(t *testing.T) {
+	var cli struct {
+		Path string `arg:"" type:"path"`
+	}
+	p := mustNew(t, &cli)
+
+	_, err := p.Parse([]string{"/an/absolute/path"})
+	require.NoError(t, err)
+	require.Equal(t, "/an/absolute/path", cli.Path)
+
+	_, err = p.Parse([]string{"-"})
+	require.NoError(t, err)
+	require.Equal(t, "-", cli.Path)
+}