Support PathFlag.TakesFile in fish completion

fish.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"reflect"
 	"strings"
 	"text/template"
 )
@@ -158,20 +159,17 @@ func (a *App) prepareFishFlags(flags []Flag, previousCommands []string) []string
 }
 
 func fishAddFileFlag(flag Flag, completion *strings.Builder) {
-	switch f := flag.(type) {
-	case *GenericFlag:
-		if f.TakesFile {
-			return
-		}
-	case *StringFlag:
-		if f.TakesFile {
-			return
-		}
-	case *StringSliceFlag:
-		if f.TakesFile {
+	val := reflect.ValueOf(flag)
+	// if flag is a non-nil pointer to a struct...
+	if val.Kind() != reflect.Invalid && val.Elem().Kind() == reflect.Struct {
+		field := val.Elem().FieldByName("TakesFile")
+		// if flag's underlying type has a bool field called TakesFile, whose value is true...
+		if field.Kind() == reflect.Bool && field.Bool() {
+			// don't append '-f'
 			return
 		}
 	}
+	// append '-f', indicating that arguments to this flag are *not* meant to be file paths
 	completion.WriteString(" -f")
 }
 

fish_test.go

@@ -7,6 +7,10 @@ import (
 func TestFishCompletion(t *testing.T) {
 	// Given
 	app := testApp()
+	app.Flags = append(app.Flags, &PathFlag{
+		Name:      "logfile",
+		TakesFile: true,
+	})
 
 	// When
 	res, err := app.ToFishCompletion()

testdata/expected-fish-full.fish

@@ -12,6 +12,7 @@ end
 complete -c greet -n '__fish_greet_no_subcommand' -l socket -s s -r -d 'some \'usage\' text'
 complete -c greet -n '__fish_greet_no_subcommand' -f -l flag -s fl -s f -r
 complete -c greet -n '__fish_greet_no_subcommand' -f -l another-flag -s b -d 'another usage text'
+complete -c greet -n '__fish_greet_no_subcommand' -l logfile -r
 complete -c greet -n '__fish_greet_no_subcommand' -f -l help -s h -d 'show help'
 complete -c greet -n '__fish_greet_no_subcommand' -f -l version -s v -d 'print the version'
 complete -c greet -n '__fish_seen_subcommand_from config c' -f -l help -s h -d 'show help'