Read a path or URL named help or h as an argument (closes #198)

On gen, check, freshen, fetch, list and export, a first argument of
`help` or `h` ran urfave/cli's built-in help command, so
`check help --require-signature FPR` printed help and passed. Those
commands now set urfave/cli's HideHelpCommand, which leaves out their
help command; the root keeps its own, so `mfer help` and
`mfer help check` still work. `check DIR --help` failed with
`No help topic for 'DIR'`; their CommandNotFound now prints the
command's own help, as `check --help` does.

Model: opus-5-5

internal/cli/mfer.go

@@ -168,6 +168,17 @@ func refuseExtraArgs(_ context.Context, cmd *cli.Command) error {
 	return nil
 }
 
+// showCommandHelp is the CommandNotFound of the commands that take a path or
+// URL. Those commands set HideHelpCommand, so that a path or URL named help or
+// h is an argument rather than urfave/cli's help command; each sets it itself,
+// because on the root it would also remove `mfer help`. With --help,
+// urfave/cli looks the command's first argument up as a help topic, so
+// `check DIR --help` asks for a topic DIR and finds none; this prints the
+// command's own help instead, as `check --help` does.
+func showCommandHelp(ctx context.Context, cmd *cli.Command, _ string) {
+	_ = cli.ShowCommandHelp(ctx, cmd.Root(), cmd.Name)
+}
+
 // requireSignatureFlag returns the --require-signature flag taken by the
 // check and fetch subcommands.
 func requireSignatureFlag() *cli.StringFlag {
@@ -191,10 +202,12 @@ func includePermissionsFlag() *cli.BoolFlag {
 
 func (mfa *CLIApp) generateCommand() *cli.Command {
 	return &cli.Command{
-		Name:      cmdGenerate,
-		Aliases:   []string{"gen"},
-		Usage:     "Generate manifest file",
-		ArgsUsage: "[path ...]",
+		Name:            cmdGenerate,
+		Aliases:         []string{"gen"},
+		Usage:           "Generate manifest file",
+		ArgsUsage:       "[path ...]",
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			mfa.setVerbosity(cmd)
 			mfa.printBanner()
@@ -253,10 +266,12 @@ func (mfa *CLIApp) generateCommand() *cli.Command {
 
 func (mfa *CLIApp) checkCommand() *cli.Command {
 	return &cli.Command{
-		Name:         cmdCheck,
-		Usage:        "Validate files using manifest file",
-		ArgsUsage:    manifestArgsUsage,
-		ArgValidator: refuseExtraArgs,
+		Name:            cmdCheck,
+		Usage:           "Validate files using manifest file",
+		ArgsUsage:       manifestArgsUsage,
+		ArgValidator:    refuseExtraArgs,
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			mfa.setVerbosity(cmd)
 			mfa.printBanner()
@@ -287,10 +302,12 @@ func (mfa *CLIApp) checkCommand() *cli.Command {
 
 func (mfa *CLIApp) freshenCommand() *cli.Command {
 	return &cli.Command{
-		Name:         cmdFreshen,
-		Usage:        "Update manifest with changed, new, and removed files",
-		ArgsUsage:    manifestArgsUsage,
-		ArgValidator: refuseExtraArgs,
+		Name:            cmdFreshen,
+		Usage:           "Update manifest with changed, new, and removed files",
+		ArgsUsage:       manifestArgsUsage,
+		ArgValidator:    refuseExtraArgs,
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			mfa.setVerbosity(cmd)
 			mfa.printBanner()
@@ -338,10 +355,12 @@ func (mfa *CLIApp) freshenCommand() *cli.Command {
 
 func (mfa *CLIApp) exportCommand() *cli.Command {
 	return &cli.Command{
-		Name:         cmdExport,
-		Usage:        "Export manifest contents as JSON",
-		ArgsUsage:    "[manifest file or URL]",
-		ArgValidator: refuseExtraArgs,
+		Name:            cmdExport,
+		Usage:           "Export manifest contents as JSON",
+		ArgsUsage:       "[manifest file or URL]",
+		ArgValidator:    refuseExtraArgs,
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			mfa.setVerbosity(cmd)
 
@@ -364,12 +383,14 @@ func (mfa *CLIApp) versionCommand() *cli.Command {
 
 func (mfa *CLIApp) listCommand() *cli.Command {
 	return &cli.Command{
-		Name:         cmdList,
-		Aliases:      []string{"ls"},
-		Usage:        "List files in manifest",
-		ArgsUsage:    manifestArgsUsage,
-		ArgValidator: refuseExtraArgs,
-		Action:       mfa.listManifestOperation,
+		Name:            cmdList,
+		Aliases:         []string{"ls"},
+		Usage:           "List files in manifest",
+		ArgsUsage:       manifestArgsUsage,
+		ArgValidator:    refuseExtraArgs,
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
+		Action:          mfa.listManifestOperation,
 		Flags: []cli.Flag{
 			&cli.BoolFlag{
 				Name:    "long",
@@ -386,10 +407,12 @@ func (mfa *CLIApp) listCommand() *cli.Command {
 
 func (mfa *CLIApp) fetchCommand() *cli.Command {
 	return &cli.Command{
-		Name:         cmdFetch,
-		Usage:        "fetch manifest and referenced files",
-		ArgsUsage:    "URL",
-		ArgValidator: refuseExtraArgs,
+		Name:            cmdFetch,
+		Usage:           "fetch manifest and referenced files",
+		ArgsUsage:       "URL",
+		ArgValidator:    refuseExtraArgs,
+		HideHelpCommand: true,
+		CommandNotFound: showCommandHelp,
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			mfa.setVerbosity(cmd)
 			mfa.printBanner()