Add filepath as an equivalent to filename which completes into subdirs.

completion.go

@@ -2,6 +2,7 @@ package flags
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
 	"reflect"
 	"sort"
@@ -48,6 +49,9 @@ type completion struct {
 // Filename is a string alias which provides filename completion.
 type Filename string
 
+// Filepath is a string alias which provides completion for file paths into subdirectories.
+type Filepath string
+
 func completionsWithoutDescriptions(items []string) []Completion {
 	ret := make([]Completion, len(items))
 
@@ -65,6 +69,18 @@ func (f *Filename) Complete(match string) []Completion {
 	return completionsWithoutDescriptions(ret)
 }
 
+// Complete returns a list of existing files with the given prefix.
+// If it completes to a single directory, the contents of that directory are interrogated.
+func (f *Filepath) Complete(match string) []Completion {
+	ret, _ := filepath.Glob(match + "*")
+	if len(ret) == 1 {
+		if info, err := os.Stat(ret[0]); err == nil && info.IsDir() {
+			ret, _ = filepath.Glob(ret[0] + "/*")
+		}
+	}
+	return completionsWithoutDescriptions(ret)
+}
+
 func (c *completion) skipPositional(s *parseState, n int) {
 	if n >= len(s.positional) {
 		s.positional = nil

completion_test.go

@@ -63,6 +63,7 @@ var completionTestOptions struct {
 	RemoveCommand struct {
 		Other bool     `short:"o"`
 		File  Filename `short:"f" long:"filename"`
+		Dir   Filepath `short:"d" long:"dir"`
 	} `command:"rm" description:"remove an item"`
 
 	RenameCommand struct {
@@ -84,6 +85,13 @@ func init() {
 
 	completionTestFilename := []string{filepath.Join(completionTestSourcedir, "completion.go"), filepath.Join(completionTestSourcedir, "completion_test.go")}
 
+	completionTestFilepath := []string{
+		filepath.Join(completionTestSourcedir, "examples/add.go"),
+		filepath.Join(completionTestSourcedir, "examples/bash-completion"),
+		filepath.Join(completionTestSourcedir, "examples/main.go"),
+		filepath.Join(completionTestSourcedir, "examples/rm.go"),
+	}
+
 	completionTests = []completionTest{
 		{
 			// Short names
@@ -227,6 +235,20 @@ func init() {
 			false,
 		},
 
+		{
+			// Flag filepath file
+			[]string{"rm", "-d", path.Join(completionTestSourcedir, "completion")},
+			completionTestFilename,
+			false,
+		},
+
+		{
+			// Flag filepath dir
+			[]string{"rm", "-d", path.Join(completionTestSourcedir, "examples")},
+			completionTestFilepath,
+			false,
+		},
+
 		{
 			// Custom completed
 			[]string{"rename", "-c", "hello un"},