Re: Broken interactive rebase text after some UTF-8 characters

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 1, 2019, 17:30 UTC
Message-ID: <xmqqpnsbzaa6.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <eda7b1c4-5fd6-5440-8998-75eab9f73e47@startmail.com>

Michal Nowak <mnowak@startmail.com> writes:

Show 11 quoted lines

>> You already have that example. Just take the UTF-8 text in your original
>> bug report, put it into something like
>>
>> 	int main(int argc, char **argv)
>> 	{
>> 		char utf8[] = "... your text here...";
>>
>> 		printf("%.*s", (int)(sizeof(utf8) - 1), utf8);
>>
>> 		return 0;
>> 	}

When replayed literally, this is not a very good test.

Show 8 quoted lines

> {global} newman@lenovo:~ $ cat printf.c
> #include <stdio.h>
> //#include <gettext.h>
> int main(int argc, char **argv) {
>   char utf8[] = "Gergő Mihály Doma\n";
>   printf("%.*s", (int)(sizeof(utf8) - 1), utf8);
>   return 0;
> }

And this is replaying it literally.

The current working suspicion in this thread is that the platform printf("%.*s", num, str) emits up to num "characters" starting at str, which is an incorrect implementation, as it should emit up to num "bytes".

Notice that the num in this case is the byte count of that utf8[] string. That number is always larger than the number of "characters" for a string with multi-byte character(s) in it. Let's say that the sample string has N "characters", and it is N+X "bytes" long, where X > 1.

If the suspicion is correct, i.e. the way the printf implementation is broken on this platform is that it shows up to num "characters", then the call is asking to show up to N+X "characters". The buggy printf shows all the available N "characters", notices the string stops there, and finishes. So you won't _see_ the bug with that test program.

Instead, use something like this.

        #include <stdio.h>

        int main(int ac, char **av)
        {
                char utf8[] = "ふabc";
                printf("%.*s\n", 4, utf8);
                return 0;
        }

With or without gettext or i18n, the output must end with 'a' followed by a newline, and you must not see 'b' nor 'c'. Otherwise your printf is broken.