feat: ShellComplete for fish

Author: marcusramberg

fish.go

@@ -34,6 +34,17 @@ func (cmd *Command) writeFishCompletionTemplate(w io.Writer) error {
 	// Add global flags
 	completions := prepareFishFlags(cmd.Name, cmd)
 
+	if cmd.ShellComplete != nil {
+		var completion strings.Builder
+		fmt.Fprintf(&completion,
+			"complete -c %s -n '%s' -xa '(%s --generate-shell-completion 2>/dev/null)'",
+			cmd.Name,
+			fishFlagHelper(cmd.Name, cmd),
+			cmd.Name,
+		)
+		completions = append(completions, completion.String())
+	}
+
 	// Add commands and their flags
 	completions = append(
 		completions,
@@ -72,6 +83,25 @@ func prepareFishCommands(binary string, parent *Command) []string {
 			}
 			completions = append(completions, completion.String())
 		}
+
+		if command.ShellComplete != nil {
+			var completion strings.Builder
+			var path []string
+			lineage := command.Lineage()
+			for i := len(lineage) - 2; i >= 0; i-- {
+				path = append(path, lineage[i].Name)
+			}
+
+			fmt.Fprintf(&completion,
+				"complete -c %s -n '%s' -xa '(%s %s --generate-shell-completion 2>/dev/null)'",
+				binary,
+				fishFlagHelper(binary, command),
+				binary,
+				strings.Join(path, " "),
+			)
+			completions = append(completions, completion.String())
+		}
+
 		completions = append(
 			completions,
 			prepareFishFlags(binary, command)...,

fish_test.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"context"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -38,3 +39,23 @@ func TestFishCompletion(t *testing.T) {
 	require.NoError(t, err)
 	expectFileContent(t, "testdata/expected-fish-full.fish", res)
 }
+
+func TestFishCompletionShellComplete(t *testing.T) {
+	cmd := buildExtendedTestCommand()
+	cmd.ShellComplete = func(context.Context, *Command) {}
+
+	configCmd := cmd.Command("config")
+	configCmd.ShellComplete = func(context.Context, *Command) {}
+
+	subConfigCmd := configCmd.Command("sub-config")
+	subConfigCmd.ShellComplete = func(context.Context, *Command) {}
+
+	cmd.setupCommandGraph()
+
+	res, err := cmd.ToFishCompletion()
+	require.NoError(t, err)
+
+	assert.Contains(t, res, "complete -c greet -n '__fish_greet_no_subcommand' -xa '(greet --generate-shell-completion 2>/dev/null)'")
+	assert.Contains(t, res, "complete -c greet -n '__fish_seen_subcommand_from config c' -xa '(greet config --generate-shell-completion 2>/dev/null)'")
+	assert.Contains(t, res, "complete -c greet -n '__fish_seen_subcommand_from config c; and __fish_seen_subcommand_from sub-config s ss' -xa '(greet config sub-config --generate-shell-completion 2>/dev/null)'")
+}