Re: [PATCH v2 1/5] git-compat-util: add isblank() and isgraph()

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 27, 2023, 19:39 UTC
Message-ID: <xmqqpm9usxrz.fsf@gitster.g>
In-Reply-To: <36cd059e-c676-2aa2-68d9-41a7b0db57f0@web.de>

René Scharfe <l.s.r@web.de> writes:

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>> In the previous submission, I just moved isblank() and isgraph() as
>> implemented in wildmatch.c. I knew they were not robust against the
>> pointer increment like isblank(*s++), but I thought it was the same
>> pattern as isprint(), which has the same issue. Unfortunately, it was
>> more controversial than I had expected...
>
> Not sure we need that story in the commit message,...

Usually we encourage people to write as if there were no "previous iterations". Describe how to reach the best end-result without any detour, using the experience gained from failed attempts.

> ... but it gave me an idea:

;-)

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> ...  So it's not so
> easy, however, ...
>
>> This version implements them as inline functions because we ran out
>> all bits in the sane_ctype[] table. This is the same pattern as
>> islower() and isupper().
>
> ... if you remove GIT_SPACE from the definition above you get a
> macro version of isgraph() that uses a single table lookup.
>
> If we're out of bits then isblank() is a good choice to implement
> without a table lookup, as this class only contains two characters
> and two comparisons should be quite fast.

Implementing sane_isblank() plus sane_isgraph() as static inlines is already not too bad, but if one of them can be made into a simple table look-up, that indeed is better ;-)

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> Stepping back a bit: Is using the unlocalized is* macros in
> wildmatch() safe, i.e. do we get the same results as before
> regardless of locale?  Junio's remark in
> https://lore.kernel.org/git/xmqq3579crsd.fsf@gitster.g/ sounds
> convincing to me if we don't care about single-byte code pages
> and require plain ASCII or UTF-8.  I think it's a good idea to
> address that point in the commit message.

True. To be honest, I wasn't thinking about non-UTF-8 single-byte "code pages". In the context of wildmatch, the strings we deal with mostly interact with the paths on the filesystem. If you interact with your filesystem in latin-1 that may pose an issue, and even if (or rather, especially if) we are to declare that it does not matter, we should document it in the proposed log message.

>
> And adding tests to t/helper/test-ctype.c would be nice.

Very true.

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>> +#define isblank(x) sane_isblank(x)
>> +#define isgraph(x) sane_isgraph(x)
>> @@ -1270,6 +1274,16 @@ static inline int sane_iscase(int x, int is_lower)
>>  		return (x & 0x20) == 0;
>>  }
>>
>> +static inline int sane_isblank(int c)
>> +{
>> +	return c == ' ' || c == '\t';
>> +}
>> +
>> +static inline int sane_isgraph(int c)
>> +{
>> +	return isprint(c) && !isspace(c);
>> +}