feat: support dynamic fish completion

autocomplete/fish_autocomplete

@@ -0,0 +1,35 @@
+# This is a shell completion script auto-generated by https://github.com/urfave/cli for fish.
+
+function __%[1]_perform_completion
+    # Extract all args except the last one
+    set -l args (commandline -opc)
+    # Extract the last arg (partial input)
+    set -l lastArg (commandline -ct)
+
+    set -l results ($args[1] $args[2..-1] $lastArg --generate-shell-completion 2> /dev/null)
+
+    # Remove trailing empty lines
+    for line in $results[-1..1]
+        if test (string trim -- $line) = ""
+            set results $results[1..-2]
+        else
+            break
+        end
+    end
+
+    for line in $results
+        if not string match -q -- "%[1]*" $line
+            set -l parts (string split -m 1 ":" -- "$line")
+            if test (count $parts) -eq 2
+                printf "%s\t%s\n" "$parts[1]" "$parts[2]"
+            else
+                printf "%s\n" "$line"
+            end
+        end
+    end
+end
+
+# Clear existing completions for %[1]
+complete -c %[1] -e
+# Register completion function
+complete -c %[1] -f -a '(__%[1]_perform_completion)'

completion.go

@@ -31,7 +31,8 @@ var (
 			return fmt.Sprintf(string(b), appName), err
 		},
 		"fish": func(c *Command, appName string) (string, error) {
-			return c.Root().ToFishCompletion()
+			b, err := autoCompleteFS.ReadFile("autocomplete/fish_autocomplete")
+			return fmt.Sprintf(string(b), appName), err
 		},
 		"pwsh": func(c *Command, appName string) (string, error) {
 			b, err := autoCompleteFS.ReadFile("autocomplete/powershell_autocomplete.ps1")

examples_test.go

@@ -409,6 +409,43 @@ func ExampleCommand_Run_shellComplete_zsh() {
 	// help:Shows a list of commands or help for one command
 }
 
+func ExampleCommand_Run_shellComplete_fish() {
+	cmd := &cli.Command{
+		Name:                  "greet",
+		EnableShellCompletion: true,
+		Commands: []*cli.Command{
+			{
+				Name:        "describeit",
+				Aliases:     []string{"d"},
+				Usage:       "use it to see a description",
+				Description: "This is how we describe describeit the function",
+				Action: func(context.Context, *cli.Command) error {
+					fmt.Printf("i like to describe things")
+					return nil
+				},
+			}, {
+				Name:        "next",
+				Usage:       "next example",
+				Description: "more stuff to see when generating bash completion",
+				Action: func(context.Context, *cli.Command) error {
+					fmt.Printf("the next example")
+					return nil
+				},
+			},
+		},
+	}
+
+	// Simulate a fish environment and command line arguments
+	os.Args = []string{"greet", "--generate-shell-completion"}
+	os.Setenv("SHELL", "/usr/bin/fish")
+
+	_ = cmd.Run(context.Background(), os.Args)
+	// Output:
+	// describeit:use it to see a description
+	// next:next example
+	// help:Shows a list of commands or help for one command
+}
+
 func ExampleCommand_Run_sliceValues() {
 	cmd := &cli.Command{
 		Name: "multi_values",

help.go

@@ -184,11 +184,12 @@ func DefaultRootCommandComplete(ctx context.Context, cmd *Command) {
 var DefaultAppComplete = DefaultRootCommandComplete
 
 func printCommandSuggestions(commands []*Command, writer io.Writer) {
+	shell := os.Getenv("SHELL")
 	for _, command := range commands {
 		if command.Hidden {
 			continue
 		}
-		if strings.HasSuffix(os.Getenv("SHELL"), "zsh") && len(command.Usage) > 0 {
+		if (strings.HasSuffix(shell, "zsh") || strings.HasSuffix(shell, "fish")) && len(command.Usage) > 0 {
 			_, _ = fmt.Fprintf(writer, "%s:%s\n", command.Name, command.Usage)
 		} else {
 			_, _ = fmt.Fprintf(writer, "%s\n", command.Name)
@@ -240,7 +241,8 @@ func printFlagSuggestions(lastArg string, flags []Flag, writer io.Writer) {
 		// match if last argument matches this flag and it is not repeated
 		if strings.HasPrefix(name, cur) && cur != name /* && !cliArgContains(name, os.Args)*/ {
 			flagCompletion := fmt.Sprintf("%s%s", strings.Repeat("-", count), name)
-			if usage != "" && strings.HasSuffix(os.Getenv("SHELL"), "zsh") {
+			shell := os.Getenv("SHELL")
+			if usage != "" && (strings.HasSuffix(shell, "zsh") || strings.HasSuffix(shell, "fish")) {
 				flagCompletion = fmt.Sprintf("%s:%s", flagCompletion, usage)
 			}
 			fmt.Fprintln(writer, flagCompletion)