Subject: Re: [GSoC] [PATCH v2 1/2] submodule--helper: introduce add-clone subcommand

From: Junio C Hamano <[email-masked]>
Date: Wed, 09 Jun 2021 13:24:38 +0900

Just a bit of random comments, leaving the full review to mentors.

> diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
> index d55f6262e9..c9cb535312 100644
> --- a/builtin/submodule--helper.c
> +++ b/builtin/submodule--helper.c
> @@ -2745,6 +2745,204 @@ static int module_set_branch(int argc, const char **argv, const char *prefix)
>  	return !!ret;
>  }
>  
> +struct add_data {
> +	const char *prefix;
> +	const char *branch;
> +	const char *reference_path;
> +	const char *sm_path;
> +	const char *sm_name;
> +	const char *repo;
> +	const char *realrepo;
> +	int depth;
> +	unsigned int force: 1;
> +	unsigned int quiet: 1;
> +	unsigned int progress: 1;
> +	unsigned int dissociate: 1;
> +};
> +#define ADD_DATA_INIT { .depth = -1 }
> +
> +static char *parse_token(char **begin, const char *end, int *tok_len)
> +{
> +	char *tok_start, *pos = *begin;

Make it a habit to have a blank line between the initial block
of declarations and the first statement.

> +	while (pos != end && (*pos != ' ' && *pos != '\t' && *pos != '\n'))
> +		pos++;
> +	tok_start = *begin;
> +	*tok_len = pos - *begin;
> +	*begin = pos + 1;
> +	return tok_start;
> +}
> +static char *get_next_line(char *const begin, const char *const end)
> +{
> +	char *pos = begin;
> +	while (pos != end && *pos++ != '\n');

Write an empty loop on two lines, like this:

	while (... condition ...)
		; /* keep scanning */

If there is a NUL byte between begin and end, this keeps going and
the resulting string will contain one.  Is that a problem?

> +	return pos;
> +}

In general, this project is mature enough that we should question
ourselves if there is already a suitable line parser we can reuse
when tempted to write another one.

> +static void show_fetch_remotes(FILE *output, const char *sm_name, const char *git_dir_path)
> +{
> +	struct child_process cp_remote = CHILD_PROCESS_INIT;
> +	struct strbuf sb_remote_out = STRBUF_INIT;
> +
> +	cp_remote.git_cmd = 1;
> +	strvec_pushf(&cp_remote.env_array,
> +		     "GIT_DIR=%s", git_dir_path);
> +	strvec_push(&cp_remote.env_array, "GIT_WORK_TREE=.");
> +	strvec_pushl(&cp_remote.args, "remote", "-v", NULL);
> +	if (!capture_command(&cp_remote, &sb_remote_out, 0)) {
> +		char *line;
> +		char *begin = sb_remote_out.buf;
> +		char *end = sb_remote_out.buf + sb_remote_out.len;
> +		while (begin != end && (line = get_next_line(begin, end))) {

OK, so this tries to parse output from "git remote -v", so NUL will
not be an issue at all.  We will get a string that is NUL terminated
and has zero or more lines, terminated with LFs.

If that is the case, I think it is far easier to read without
a custom get-next-line wrapper, e.g.

	for (this_line = begin;
	     *this_line;
	     this_line = next_line) {
		next_line = strchrnul(this_line, '\n');
		... process bytes between this_line..next_line ...
	}                

> +			int namelen = 0, urllen = 0, taillen = 0;
> +			char *name = parse_token(&begin, line, &namelen);

Similarly, consider if strcspn() is useful in implementing
parse_token().  See how existing code uses the standard system
function with

	$ git grep strcspn \*.c

> +			char *url = parse_token(&begin, line, &urllen);
> +			char *tail = parse_token(&begin, line, &taillen);
> +			if (!memcmp(tail, "(fetch)", 7))

At this point do we know there are enough number of bytes after
tail[0] to allow us to do this comparison safely?  Otherwise,

			if (starts_with(tail, "(fetch)")

may be preferrable.