feat: suggest similar flags for an unknown flag

tea issue list --lable bug now fails with "unknown flag: --lable; did
you mean --label?". Suggestions are the command's visible flags that
start with the typed name or are at most two edits away from it.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/app.go

@@ -103,7 +103,7 @@ func NewRoot(deps Dependencies) *cobra.Command {
 	root.SetIn(deps.Streams.In)
 	root.SetOut(deps.Streams.Out)
 	root.SetErr(deps.Streams.ErrOut)
-	root.SetFlagErrorFunc(func(_ *cobra.Command, err error) error { return clierr.Wrap(clierr.Usage, err) })
+	root.SetFlagErrorFunc(func(cmd *cobra.Command, err error) error { return clierr.Wrap(clierr.Usage, suggestFlags(cmd, err)) })
 	flags := root.PersistentFlags()
 	flags.StringVar(&a.options.host, "host", "", "Gitea instance `URL`, including any base path")
 	flags.StringVar(&a.options.user, "user", "", "Account `name` on the selected instance")
@@ -215,6 +215,46 @@ func flagAliases(cmd *cobra.Command, aliases map[string]string) {
 	})
 }
 
+// suggestFlags adds the flags of cmd with a similar name to an unknown flag error, as in
+// "unknown flag: --lable; did you mean --label?".
+func suggestFlags(cmd *cobra.Command, err error) error {
+	name, unknown := strings.CutPrefix(err.Error(), "unknown flag: --")
+	if !unknown || len(name) < 3 {
+		return err
+	}
+	var suggestions []string
+	cmd.Flags().VisitAll(func(flag *pflag.Flag) {
+		if !flag.Hidden && (strings.HasPrefix(flag.Name, name) || editDistance(name, flag.Name) <= 2) {
+			suggestions = append(suggestions, "--"+flag.Name)
+		}
+	})
+	if len(suggestions) == 0 {
+		return err
+	}
+	return fmt.Errorf("%w; did you mean %s?", err, strings.Join(suggestions, " or "))
+}
+
+// editDistance counts the single-character insertions, deletions and substitutions that turn a into b.
+func editDistance(a, b string) int {
+	row := make([]int, len(b)+1)
+	for j := range row {
+		row[j] = j
+	}
+	for i := 1; i <= len(a); i++ {
+		diagonal := row[0]
+		row[0] = i
+		for j := 1; j <= len(b); j++ {
+			substitution := diagonal
+			if a[i-1] != b[j-1] {
+				substitution++
+			}
+			diagonal = row[j]
+			row[j] = min(row[j]+1, row[j-1]+1, substitution)
+		}
+	}
+	return row[len(b)]
+}
+
 // checkOutputFlags validates --json and --jq before a command runs. --jq alone selects every field,
 // except on commands that filter their raw JSON themselves (annotation tea.rawjson).
 func (a *application) checkOutputFlags(cmd *cobra.Command) error {

internal/app/app_test.go

@@ -196,6 +196,22 @@ func TestRawJSONCommandsKeepJQToThemselves(t *testing.T) {
 	require.ErrorContains(t, root.Execute(), "raw prints text; --json is not supported")
 }
 
+func TestUnknownFlagsSuggestSimilarFlags(t *testing.T) {
+	requireUsageBeforeRequests(t, "unknown flag: --lable; did you mean --label?", "issue", "list", "--lable", "bug")
+	requireUsageBeforeRequests(t, "unknown flag: --stat; did you mean --state?", "issue", "list", "--stat", "open")
+	requireUsageBeforeRequests(t, "unknown flag: --add-label; did you mean --add-labels?", "issue", "edit", "1", "--add-label", "bug")
+	deps, _, _ := testDeps(t)
+	err := Execute(context.Background(), deps, []string{"issue", "list", "--zzzzzz"})
+	require.Equal(t, clierr.Usage, clierr.ExitCode(err))
+	require.EqualError(t, err, "unknown flag: --zzzzzz")
+	for _, tc := range []struct {
+		a, b     string
+		distance int
+	}{{"kitten", "sitting", 3}, {"", "abc", 3}, {"label", "label", 0}, {"lable", "label", 2}} {
+		require.Equal(t, tc.distance, editDistance(tc.a, tc.b), tc)
+	}
+}
+
 func TestRootHelpGroupsCommandsAndTopics(t *testing.T) {
 	deps, out, _ := testDeps(t)
 	require.NoError(t, Execute(context.Background(), deps, []string{"alias", "set", "co", "pr checkout"}))