Subject: Re: [PATCH 09/20] parse-options: add support for parsing subcommands

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Mon, 25 Jul 2022 16:43:30 +0200

On Mon, Jul 25 2022, SZEDER Gábor wrote:

> Several Git commands have subcommands to implement mutually exclusive
> "operation modes", and they usually parse their subcommand argument
> with a bunch of if-else if statements.

I'll need do look this over in more details, just some comments on the
non-meaty parts for now:

> diff --git a/builtin/blame.c b/builtin/blame.c
> index 02e39420b6..a9fe8cf7a6 100644
> --- a/builtin/blame.c
> +++ b/builtin/blame.c
> @@ -920,6 +920,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
>  			break;
>  		case PARSE_OPT_HELP:
>  		case PARSE_OPT_ERROR:
> +		case PARSE_OPT_SUBCOMMAND:
>  			exit(129);
>  		case PARSE_OPT_COMPLETE:
>  			exit(0);
> diff --git a/builtin/shortlog.c b/builtin/shortlog.c
> index 086dfee45a..7a1e1fe7c0 100644
> --- a/builtin/shortlog.c
> +++ b/builtin/shortlog.c
> @@ -381,6 +381,7 @@ int cmd_shortlog(int argc, const char **argv, const char *prefix)
>  			break;
>  		case PARSE_OPT_HELP:
>  		case PARSE_OPT_ERROR:
> +		case PARSE_OPT_SUBCOMMAND:
>  			exit(129);
>  		case PARSE_OPT_COMPLETE:
>  			exit(0);

This feels a bit like carrying forward an API wart, i.e. shouldn't we
instead BUG() if we are returning a PARSE_OPT_SUBCOMMAND from
parse_options_step() for options lists that don't have
PARSE_OPT_SUBCOMMAND in them?

I.e. is this even reachable, or just something to suppress the compiler
complaining about missing enum labels?

>  static void check_typos(const char *arg, const struct option *options)
>  {
>  	if (strlen(arg) < 3)
> @@ -442,6 +457,7 @@ static void check_typos(const char *arg, const struct option *options)
>  static void parse_options_check(const struct option *opts)
>  {
>  	char short_opts[128];
> +	void *subcommand_value = NULL;
>  
>  	memset(short_opts, '\0', sizeof(short_opts));
>  	for (; opts->type != OPTION_END; opts++) {
> @@ -489,6 +505,14 @@ static void parse_options_check(const struct option *opts)
>  			       "Are you using parse_options_step() directly?\n"
>  			       "That case is not supported yet.");
>  			break;
> +		case OPTION_SUBCOMMAND:
> +			if (!opts->value || !opts->subcommand_fn)
> +				optbug(opts, "OPTION_SUBCOMMAND needs a value and a subcommand function");
> +			if (!subcommand_value)
> +				subcommand_value = opts->value;
> +			else if (subcommand_value != opts->value)
> +				optbug(opts, "all OPTION_SUBCOMMANDs need the same value");
> +			break;
>  		default:
>  			; /* ok. (usually accepts an argument) */
>  		}

This addition looks good...

> @@ -499,6 +523,14 @@ static void parse_options_check(const struct option *opts)
>  	BUG_if_bug("invalid 'struct option'");
>  }
>  
> +static int has_subcommands(const struct option *options)
> +{
> +	for (; options->type != OPTION_END; options++)
> +		if (options->type == OPTION_SUBCOMMAND)
> +			return 1;
> +	return 0;
> +}

...but why not...

>  static void parse_options_start_1(struct parse_opt_ctx_t *ctx,
>  				  int argc, const char **argv, const char *prefix,
>  				  const struct option *options,
> @@ -515,6 +547,19 @@ static void parse_options_start_1(struct parse_opt_ctx_t *ctx,
>  	ctx->prefix = prefix;
>  	ctx->cpidx = ((flags & PARSE_OPT_KEEP_ARGV0) != 0);
>  	ctx->flags = flags;
> +	ctx->has_subcommands = has_subcommands(options);
> +	if (!ctx->has_subcommands && (flags & PARSE_OPT_SUBCOMMAND_OPTIONAL))
> +		BUG("Using PARSE_OPT_SUBCOMMAND_OPTIONAL without subcommands");
> +	if (ctx->has_subcommands) {
> +		if (flags & PARSE_OPT_STOP_AT_NON_OPTION)
> +			BUG("subcommands are incompatible with PARSE_OPT_STOP_AT_NON_OPTION");
> +		if (!(flags & PARSE_OPT_SUBCOMMAND_OPTIONAL)) {
> +			if (flags & PARSE_OPT_KEEP_UNKNOWN_OPT)
> +				BUG("subcommands are incompatible with PARSE_OPT_KEEP_UNKNOWN unless in combination with PARSE_OPT_SUBCOMMAND_OPTIONAL");
> +			if (flags & PARSE_OPT_KEEP_DASHDASH)
> +				BUG("subcommands are incompatible with PARSE_OPT_KEEP_DASHDASH unless in combination with PARSE_OPT_SUBCOMMAND_OPTIONAL");
> +		}
> +	}

...move this into parse_options_check()? I.e. we'd need to loop over the
list once, but it seems like this should belong there.

We have an existing bug in-tree due to usage_with_options() not doing a
parse_options_check() (I have a local fix...), checking this sort of
thing there instead of in parse_options_start() is therefore the right
thing to do, i.e. we shoudl have a one-stop "does this options variable
look sane?".

> +				error(_("unknown subcommand: %s"), arg);

s/%s/'%s'/ while we're at it, perhaps?

> +				usage_with_options(usagestr, options);
> +			case PARSE_OPT_COMPLETE:
> +			case PARSE_OPT_HELP:
> +			case PARSE_OPT_ERROR:
> +			case PARSE_OPT_DONE:
> +			case PARSE_OPT_NON_OPTION:
> +				BUG("parse_subcommand() cannot return these");

nit: BUG("got bad %d", v) or whatever, i.e. say what we got?

> @@ -206,6 +217,11 @@ struct option {
>  #define OPT_ALIAS(s, l, source_long_name) \
>  	{ OPTION_ALIAS, (s), (l), (source_long_name) }
>  
> +#define OPT_SUBCOMMAND(l, v, fn)      { OPTION_SUBCOMMAND, 0, (l), (v), NULL, \
> +					NULL, 0, NULL, 0, NULL, 0, (fn) }
> +#define OPT_SUBCOMMAND_F(l, v, fn, f) { OPTION_SUBCOMMAND, 0, (l), (v), NULL, \
> +					NULL, (f), NULL, 0, NULL, 0, (fn) }

Nit, I know you're carrying forward existing patterns, but since that
all pre-dated designated init perhaps we could just (untested):
	
	#define OPT_SUBCOMMAND_F(l, v, fn, f) { \
		.type = OPTION_SUBCOMMAND, \
		.long_name = (l), \
		.value = (v), \
		.ll_callback = (fn), \
	}
	#define OPT_SUBCOMMAND(l, v, fn) OPT_SUBCOMMAND_F((l), (v), (fn), 0)

Which IMO is much nicer. I have some patches somewhere to convert these
to saner patterns (I think not designated init, but the X() can be
defined in terms of X_F() like that, but since this is new we can use
designated init all the way...

> +{
> +	int i;

Nit: missing \n (usual style of variable decl);

> +		error("'cmd' is mandatory");
> +		usage_with_options(usage, test_flag_options);

nit: I think you want usage_msg_optf() or usage_msg_opt().

> +test_expect_success 'subcommand - no subcommand shows error and usage' '
> +	test_expect_code 129 test-tool parse-subcommand cmd 2>err &&
> +	grep "^error: need a subcommand" err &&
> +	grep ^usage: err
> +'
> +
> +test_expect_success 'subcommand - subcommand after -- shows error and usage' '
> +	test_expect_code 129 test-tool parse-subcommand cmd -- subcmd-one 2>err &&
> +	grep "^error: need a subcommand" err &&
> +	grep ^usage: err
> +'
> +
> +test_expect_success 'subcommand - subcommand after --end-of-options shows error and usage' '
> +	test_expect_code 129 test-tool parse-subcommand cmd --end-of-options subcmd-one 2>err &&
> +	grep "^error: need a subcommand" err &&
> +	grep ^usage: err
> +'
> +
> +test_expect_success 'subcommand - unknown subcommand shows error and usage' '
> +	test_expect_code 129 test-tool parse-subcommand cmd nope 2>err &&
> +	grep "^error: unknown subcommand: nope" err &&
> +	grep ^usage: err
> +'
> +
> +test_expect_success 'subcommand - subcommands cannot be abbreviated' '
> +	test_expect_code 129 test-tool parse-subcommand cmd subcmd-o 2>err &&
> +	grep "^error: unknown subcommand: subcmd-o$" err &&
> +	grep ^usage: err
> +'
> +
> +test_expect_success 'subcommand - no negated subcommands' '
> +	test_expect_code 129 test-tool parse-subcommand cmd no-subcmd-one 2>err &&
> +	grep "^error: unknown subcommand: no-subcmd-one" err &&
> +	grep ^usage: err
> +'

Creating a trivial helper for this seems worthile, then something like:

	that_helper "expected error here" -- arg u ments to test-tool parse-subcommand

> +test_expect_success 'subcommand - simple' '
> +	test-tool parse-subcommand cmd subcmd-two >actual &&
> +	cat >expect <<-\EOF &&
> +	opt: 0
> +	fn: subcmd_two
> +	arg 00: subcmd-two
> +	EOF
> +	test_cmp expect actual
> +'

Ditto, perhaps? I.e.

	new_hepler arg u ments <<-\EOF
        expected
        goes here
       	EOF