Re: [PATCH v2 5/7] quote: add sq_quote_argv_pretty_ltrim

From: Jeff Hostetler <git@jeffhostetler.com>
Date: Aug 8, 2019, 19:04 UTC
Message-ID: <7dbee619-2495-6426-b02b-49fd59e4f028@jeffhostetler.com>
In-Reply-To: <xmqqh86rfs70.fsf@gitster-ct.c.googlers.com>

On 8/8/2019 2:05 PM, Junio C Hamano wrote:

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> "Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Create version of sq_quote_argv_pretty() that does not
>> insert a leading space before argv[0].
>>
>> Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
>> ---
>>   quote.c | 11 +++++++++++
>>   quote.h |  1 +
>>   2 files changed, 12 insertions(+)
> 
> I am OK with the basic idea, but I am somewhat unhappy about this
> particular patch for two reasons:
> 
>   - If we were to keep this as a part of proper API in the longer
>     term, the current sq_quote_argv_pretty() should be rewritten to
>     use this to avoid repetition (e.g. as long as !!*argv, add a SP
>     and then call this new thing);
> 
>   - something_ltrim() sounds as if you munge what is passed to you
>     and chop off the left end, but that is not what this does.
> 
> Now, what is the right name for this new thing?  What does it do?

I struggled with the proper name for this. And even thought about adding a 3rd arg to the current function to indicate whether to have the leading SP before argv[0], but wasn't sure if that was too disruptive.

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> 
> It looks to me that it appends each element of argv[], quoting it as
> needed, and with SP in between.  So the right name for the family of
> these functions should be around "append", which is the primary thing
> they do, with "quoted" somewhere.
> 
> Having made the primary purpose of the helper clearer leads me to
> wonder if "do not add SP before the first element, i.e. argv[0]", is
> really what we want.  If we always clear the *dst strbuf before
> starting to serialize argv[] into it, then the behaviour would make
> sense, but we do not---we are "appending".
> 
> As long as we are appending, would we be better off doing something
> sillily magical like this instead, I have to wonder?
> 
> 	void sq_append_strings_quoted(struct strbuf *buf, const char **av)
> 	{
> 		int i;
> 
> 		for (i = 0; av[i]; i++) {
> 			if (buf->len)
> 				strbuf_addch(buf, ' ');
> 			sq_quote_buf_pretty(buf, argv[0]);
> 		}
> 	}
> 
> That is, "if we are appending to an existing string, have SP to
> separate the first element from that existing string; treat the
> remaining elements the same way (if the buffer is empty, there is no
> point adding SP at the beginning)".

I don't think that would do what we want. We don't know what the caller's expectations are. In my uses in commits 6/7 and 7/7 I already added the leading chars I wanted in the strbuf before calling sq_quote_argv_pretty_ltrim() and assumed the output would be a true append. For example:

+ strbuf_addf(&buf_payload, "alias:%s argv:[", alias); + sq_quote_argv_pretty_ltrim(&buf_payload, argv); + strbuf_addch(&buf_payload, ']');

I like your suggestion of putting my new function in the _append_ category. I think I'll add the 3rd arg to this and then it will be completely specified and I can get rid of the _ltrim suffix.

I'll re-roll this.

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> 
> I may have found a long-standing bug in sq_quote_buf_pretty(), by
> the way.  What does it produce when *src is an empty string of
> length 0?  It does not add anything to dst, but shouldn't we be
> adding two single-quotes (i.e. an empty string inside sq pair)?

I would think so. I did a quick grep and most of the calls looked guarded, so I don't think this is urgent. I'll address this in a separate commit shortly.

Thanks Jeff

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> 
>> diff --git a/quote.c b/quote.c
>> index 7f2aa6faa4..7cad8798ac 100644
>> --- a/quote.c
>> +++ b/quote.c
>> @@ -94,6 +94,17 @@ void sq_quote_argv_pretty(struct strbuf *dst, const char **argv)
>>   	}
>>   }
>>   
>> +void sq_quote_argv_pretty_ltrim(struct strbuf *dst, const char **argv)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; argv[i]; i++) {
>> +		if (i > 0)
>> +			strbuf_addch(dst, ' ');
>> +		sq_quote_buf_pretty(dst, argv[i]);
>> +	}
>> +}
>> +
>>   static char *sq_dequote_step(char *arg, char **next)
>>   {
>>   	char *dst = arg;
>> diff --git a/quote.h b/quote.h
>> index fb08dc085c..3b3d041a61 100644
>> --- a/quote.h
>> +++ b/quote.h
>> @@ -40,6 +40,7 @@ void sq_quotef(struct strbuf *, const char *fmt, ...);
>>    */
>>   void sq_quote_buf_pretty(struct strbuf *, const char *src);
>>   void sq_quote_argv_pretty(struct strbuf *, const char **argv);
>> +void sq_quote_argv_pretty_ltrim(struct strbuf *, const char **argv);
>>   
>>   /* This unwraps what sq_quote() produces in place, but returns
>>    * NULL if the input does not look like what sq_quote would have