Subject: Re: [PATCH v3] help: make option --help open man pages only for Git commands

From: Junio C Hamano <[email-masked]>
Date: Tue, 16 Aug 2016 10:27:35 -0700

Ralf Thielow <[email-masked]> writes:

>  builtin/help.c  | 30 +++++++++++++++++++++++-------
>  git.c           | 15 ++++++++++++++-
>  t/t0012-help.sh | 15 +++++++++++++++
>  3 files changed, 52 insertions(+), 8 deletions(-)
>  create mode 100755 t/t0012-help.sh
>
> diff --git a/builtin/help.c b/builtin/help.c
> index 8848013..76f07c7 100644
> --- a/builtin/help.c
> +++ b/builtin/help.c
> @@ -37,7 +37,9 @@ static int show_all = 0;
>  static int show_guides = 0;
>  static unsigned int colopts;
>  static enum help_format help_format = HELP_FORMAT_NONE;
> +static int swapped = 0;

This is not the first offender (show_guides above does so, too), but
please do not initialize static explicitly to 0 or NULL.

>  static struct option builtin_help_options[] = {
> +	OPT_BOOL('s', "swapped", &swapped, "mark as being called by <cmd> --help"),
>  	OPT_BOOL('a', "all", &show_all, N_("print all available commands")),
>  	OPT_BOOL('g', "guides", &show_guides, N_("print list of useful guides")),
>  	OPT_SET_INT('m', "man", &help_format, N_("show man page"), HELP_FORMAT_MAN),
> @@ -433,10 +435,29 @@ static void list_common_guides_help(void)
>  	putchar('\n');
>  }
>  
> +static const char* check_git_cmd(const char* cmd)

Style: "static const char *check_git_cmd(const char *cmd)".  The
asterisk that turns the base type to a pointer to the base type
sticks to the identifier, not to the type.

> +{
> +	char *alias;
> +
> +	if (is_git_command(cmd))
> +		return cmd;
> +
> +	alias = alias_lookup(cmd);
> +	if (alias) {
> +		printf_ln(_("`git %s' is aliased to `%s'"), cmd, alias);
> +		free(alias);
> +		exit(0);
> +	}
> +
> +	if (swapped)
> +		return help_unknown_cmd(cmd);

I am guilty of suggesting "swapped"; even if we are going to mark
this as OPT_HIDDEN, I think we should be able to think of a better
name.  I think the meaning of this boolean is "we know that this is
not a guide and is meant to be a command.", and I hope we can come
up with a name that concisely expresses that (e.g. "--not-a-guide",
"--must-be-a-command").

> +	return cmd;
> +}
> +
>  int cmd_help(int argc, const char **argv, const char *prefix)
>  {
>  	int nongit;
> -	char *alias;
>  	enum help_format parsed_help_format;
>  
>  	argc = parse_options(argc, argv, prefix, builtin_help_options,
> @@ -476,12 +497,7 @@ int cmd_help(int argc, const char **argv, const char *prefix)
>  	if (help_format == HELP_FORMAT_NONE)
>  		help_format = parse_help_format(DEFAULT_HELP_FORMAT);
>  
> -	alias = alias_lookup(argv[0]);
> -	if (alias && !is_git_command(argv[0])) {
> -		printf_ln(_("`git %s' is aliased to `%s'"), argv[0], alias);
> -		free(alias);
> -		return 0;
> -	}
> +	argv[0] = check_git_cmd(argv[0]);
>  
>  	switch (help_format) {
>  	case HELP_FORMAT_NONE:
> diff --git a/git.c b/git.c
> index 0f1937f..71ea983 100644
> --- a/git.c
> +++ b/git.c
> @@ -528,10 +528,23 @@ static void handle_builtin(int argc, const char **argv)
>  	strip_extension(argv);
>  	cmd = argv[0];
>  
> -	/* Turn "git cmd --help" into "git help cmd" */
> +	/* Turn "git cmd --help" into "git help --swapped cmd" */
>  	if (argc > 1 && !strcmp(argv[1], "--help")) {
> +		struct argv_array args;
> +		int i;
> +
>  		argv[1] = argv[0];
>  		argv[0] = cmd = "help";
> +
> +		argv_array_init(&args);
> +		for (i = 0; i < argc; i++) {
> +			argv_array_push(&args, argv[i]);
> +			if (i == 0)

It is more idiomatic to say

			if (!i)

around here.

> +				argv_array_push(&args, "--swapped");

> +		}
> +
> +		argc++;
> +		argv = argv_array_detach(&args);
>  	}
>  
>  	builtin = get_builtin(cmd);

The code does this after it:

	if (builtin)
        	exit(run_builtin(...));

and returns.  If we didn't get builtin, we risk leaking args.argv
here, but we assume argv[0] = cmd = "help" is always a builtin,
which I think is a safe assumption, so the code is OK.  Static
checkers that are only half intelligent may yell at you for not
releasing the resources, though.

> diff --git a/t/t0012-help.sh b/t/t0012-help.sh
> new file mode 100755
> index 0000000..6f700b1
> --- /dev/null
> +++ b/t/t0012-help.sh
> @@ -0,0 +1,15 @@
> +#!/bin/sh
> +
> +test_description='help'
> +
> +. ./test-lib.sh
> +
> +test_expect_success "pass --help to common guide" "
> +	cat <<-EOF >expected &&
> +		git: 'revisions' is not a git command. See 'git --help'.
> +	EOF
> +	(git revisions --help 2>actual || true) &&
> +	test_i18ncmp expected actual
> +"
> +
> +test_done