Re: [PATCH v5 6/8] config: parse more robust format in GIT_CONFIG_PARAMETERS

> From: Jeff King <peff@peff.net>
> 
> When we stuff config options into GIT_CONFIG_PARAMETERS, we shell-quote
> each one as a single unit, like:
> 
>    'section.one=value1' 'section.two=value2'
> 
> On the reading side, we de-quote to get the individual strings, and then
> parse them by splitting on the first "=" we find. This format is
> ambiguous, because an "=" may appear in a subsection. So the config
> represented in a file by both:
> 
>    [section "subsection=with=equals"]
>    key = value
> 
> and:
> 
>    [section]
>    subsection = with=equals.key=value
> 
> ends up in this flattened format like:
> 
>    'section.subsection=with=equals.key=value'
> 
> and we can't tell which was desired. We have traditionally resolved this
> by taking the first "=" we see starting from the left, meaning that we
> allowed arbitrary content in the value, but not in the subsection.

> Let's make our environment format a bit more robust by separately
> quoting the key and value. That turns those examples into:
> 
>    'section.subsection=with=equals.key'='value'
> 
> and:
> 
>    'section.subsection'='with=equals.key=value'
> 
> respectively, and we can tell the difference between them. We can detect
> which format is in use for any given element of the list based on the
> presence of the unquoted "=". That means we can continue to allow the
> old format to work to support any callers which manually used the old
> format, and we can even intermingle the two formats. The old format
> wasn't documented, and nobody was supposed to be using it. But it's
> likely that such callers exist in the wild, so it's nice if we can avoid
> breaking them. Likewise, it may be possible to trigger an older version
> of "git -c" that runs a script that calls into a newer version of "git
> -c"; that new version would see the intermingled format.
> 
> This does create one complication, which is that the obvious format in
> the new scheme for
> 
>    [section]
>    some-bool
> 
> is:
> 
>    'section.some-bool'
> 
> with no equals. We'd mistake that for an old-style variable. And it even
> has the same meaning in the old style, but:
> 
>    [section "with=equals"]
>    some-bool
> 
> does not. It would be:
> 
>    'section.with=equals=some-bool'
> 
> which we'd take to mean:
> 
>    [section]
>    with = equals=some-bool
> 
> in the old, ambiguous style. Likewise, we can't use:
> 
>    'section.some-bool'=''
> 
> because that's ambiguous with an actual empty string. Instead, we'll
> again use the shell-quoting to give us a hint, and use:
> 
>    'section.some-bool'=
> 
> to show that we have no value.
> 
> Note that this commit just expands the reading side. We'll start writing
> the new format via "git -c" in a future patch. In the meantime, the
> existing "git -c" tests will make sure we didn't break reading the old
> format. But we'll also add some explicit coverage of the two formats to
> make sure we continue to handle the old one after we move the writing
> side over.
> 
> And one final note: since we're now using the shell-quoting as a
> semantically meaningful hint, this closes the door to us ever allowing
> arbitrary shell quoting, like:
> 
>    'a'shell'would'be'ok'with'this'.key=value
> 
> But we have never supported that (only what sq_quote() would produce),
> and we are probably better off keeping things simple, robust, and
> backwards-compatible, than trying to make it easier for humans. We'll
> continue not to advertise the format of the variable to users, and
> instead keep "git -c" as the recommended mechanism for setting config
> (even if we are trying to be kind not to break users who may be relying
> on the current undocumented format).
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>   config.c          | 69 +++++++++++++++++++++++++++++++++++------------
>   t/t1300-config.sh | 52 +++++++++++++++++++++++++++++++++++
>   2 files changed, 104 insertions(+), 17 deletions(-)
> 
> diff --git a/config.c b/config.c
> index 53ed048689..60a7261807 100644
> --- a/config.c
> +++ b/config.c
> @@ -541,14 +541,62 @@ int git_config_parse_parameter(const char *text,
>   	return ret;
>   }
>   
> +static int parse_config_env_list(char *env, config_fn_t fn, void *data)
> +{
> +	char *cur = env;
> +	while (cur && *cur) {
> +		const char *key = sq_dequote_step(cur, &cur);
> +		if (!key)
> +			return error(_("bogus format in %s"),
> +				     CONFIG_DATA_ENVIRONMENT);
> +
> +		if (!cur || isspace(*cur)) {
> +			/* old-style 'key=value' */
> +			if (git_config_parse_parameter(key, fn, data) < 0)
> +				return -1;
> +		}
> +		else if (*cur == '=') {
> +			/* new-style 'key'='value' */
> +			const char *value;
> +
> +			cur++;
> +			if (*cur == '\'') {
> +				/* quoted value */
> +				value = sq_dequote_step(cur, &cur);
> +				if (!value || (cur && !isspace(*cur))) {
> +					return error(_("bogus format in %s"),
> +						     CONFIG_DATA_ENVIRONMENT);
> +				}
> +			} else if (!*cur || isspace(*cur)) {
> +				/* implicit bool: 'key'= */
> +				value = NULL;
> +			} else {
> +				return error(_("bogus format in %s"),
> +					     CONFIG_DATA_ENVIRONMENT);
> +			}
> +
> +			if (config_parse_pair(key, value, fn, data) < 0)
> +				return -1;
> +		}
> +		else {
> +			/* unknown format */
> +			return error(_("bogus format in %s"),
> +				     CONFIG_DATA_ENVIRONMENT);
> +		}
> +
> +		if (cur) {
> +			while (isspace(*cur))
> +				cur++;
> +		}
> +	}
> +	return 0;
> +}
> +
>   int git_config_from_parameters(config_fn_t fn, void *data)
>   {
>   	const char *env = getenv(CONFIG_DATA_ENVIRONMENT);
>   	int ret = 0;
>   	char *envw;
> -	const char **argv = NULL;
> -	int nr = 0, alloc = 0;
> -	int i;
>   	struct config_source source;
>   
>   	if (!env)
> @@ -561,21 +609,8 @@ int git_config_from_parameters(config_fn_t fn, void *data)
>   
>   	/* sq_dequote will write over it */
>   	envw = xstrdup(env);
> +	ret = parse_config_env_list(envw, fn, data);
>   
> -	if (sq_dequote_to_argv(envw, &argv, &nr, &alloc) < 0) {
> -		ret = error(_("bogus format in %s"), CONFIG_DATA_ENVIRONMENT);
> -		goto out;
> -	}
> -
> -	for (i = 0; i < nr; i++) {
> -		if (git_config_parse_parameter(argv[i], fn, data) < 0) {
> -			ret = -1;
> -			goto out;
> -		}
> -	}
> -
> -out:
> -	free(argv);
>   	free(envw);
>   	cf = source.prev;
>   	return ret;
> diff --git a/t/t1300-config.sh b/t/t1300-config.sh
> index 36a60879f6..35a1a6e8b1 100755
> --- a/t/t1300-config.sh
> +++ b/t/t1300-config.sh
> @@ -1294,6 +1294,58 @@ test_expect_success 'git -c is not confused by empty environment' '
>   	GIT_CONFIG_PARAMETERS="" git -c x.one=1 config --list
>   '
>   
> +test_expect_success 'GIT_CONFIG_PARAMETERS handles old-style entries' '
> +	v="${SQ}key.one=foo${SQ}" &&
> +	v="$v  ${SQ}key.two=bar${SQ}" &&
> +	v="$v ${SQ}key.ambiguous=section.whatever=value${SQ}" &&
> +	GIT_CONFIG_PARAMETERS=$v git config --get-regexp "key.*" >actual &&
> +	cat >expect <<-EOF &&
> +	key.one foo
> +	key.two bar
> +	key.ambiguous section.whatever=value
> +	EOF
> +	test_cmp expect actual
> +'
> +
> +test_expect_success 'GIT_CONFIG_PARAMETERS handles new-style entries' '
> +	v="${SQ}key.one${SQ}=${SQ}foo${SQ}" &&
> +	v="$v  ${SQ}key.two${SQ}=${SQ}bar${SQ}" &&
> +	v="$v ${SQ}key.ambiguous=section.whatever${SQ}=${SQ}value${SQ}" &&
> +	GIT_CONFIG_PARAMETERS=$v git config --get-regexp "key.*" >actual &&
> +	cat >expect <<-EOF &&
> +	key.one foo
> +	key.two bar
> +	key.ambiguous=section.whatever value
> +	EOF
> +	test_cmp expect actual
> +'
> +
> +test_expect_success 'old and new-style entries can mix' '
> +	v="${SQ}key.oldone=oldfoo${SQ}" &&
> +	v="$v ${SQ}key.newone${SQ}=${SQ}newfoo${SQ}" &&
> +	v="$v ${SQ}key.oldtwo=oldbar${SQ}" &&
> +	v="$v ${SQ}key.newtwo${SQ}=${SQ}newbar${SQ}" &&
> +	GIT_CONFIG_PARAMETERS=$v git config --get-regexp "key.*" >actual &&
> +	cat >expect <<-EOF &&
> +	key.oldone oldfoo
> +	key.newone newfoo
> +	key.oldtwo oldbar
> +	key.newtwo newbar
> +	EOF
> +	test_cmp expect actual
> +'
> +
> +test_expect_success 'old and new bools with ambiguous subsection' '
> +	v="${SQ}key.with=equals.oldbool${SQ}" &&
> +	v="$v ${SQ}key.with=equals.newbool${SQ}=" &&
> +	GIT_CONFIG_PARAMETERS=$v git config --get-regexp "key.*" >actual &&
> +	cat >expect <<-EOF &&
> +	key.with equals.oldbool
> +	key.with=equals.newbool
> +	EOF
> +	test_cmp expect actual
> +'
> +
>   test_expect_success 'detect bogus GIT_CONFIG_PARAMETERS' '
>   	cat >expect <<-\EOF &&
>   	env.one one
>