Tomi Ollila <tomi.ollila@iki.fi> writes:

> On Fri, Dec 02 2022, Thomas Schneider wrote:
>
>> As per strcasestr(3) of glibc and FreeBSD, the header that defines
>> strcasestr() is string.h, not strings.h.  This may cause compilation,
>> and thus detection whether an (optimised) version is available, to
>> fail even if the function is available, when implicit declaration and
>> pointer conversion do not match.
>>
>> Signed-off-by: Thomas Schneider <qsx@chaotikum.eu>
>> ---
>> I discovered this when building with Clang:
>>
>> qsx@naboo ~/src/notmuch (git)-[tags/0.32.2]
>> % gcc -o /dev/null compat/have_strcasestr.c; echo $?
>> compat/have_strcasestr.c: In function ‘main’:
>> compat/have_strcasestr.c:10:13: warning: implicit declaration of function ‘strcasestr’; did you mean ‘strcasecmp’? [-Wimplicit-function-declaration]
>>    10 |     found = strcasestr (haystack, needle);
>>       |             ^~~~~~~~~~
>>       |             strcasecmp
>> compat/have_strcasestr.c:10:11: warning: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
>>    10 |     found = strcasestr (haystack, needle);
>>       |           ^
>> 0
>> qsx@naboo ~/src/notmuch (git)-[tags/0.32.2]
>> % clang -o /dev/null compat/have_strcasestr.c; echo $?
>> compat/have_strcasestr.c:10:13: warning: call to undeclared function 'strcasestr'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>>     found = strcasestr (haystack, needle);
>>             ^
>> compat/have_strcasestr.c:10:11: error: incompatible integer to pointer conversion assigning to 'char *' from 'int' [-Wint-conversion]
>>     found = strcasestr (haystack, needle);
>>           ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 1 warning and 1 error generated.
>> 1
>>
>> configure then assumes strcasestr is not available when using Clang, so it
>> builds the variant from compat/, which later fails when linking because of
>> conflicting symbols.
>>
>> On a side note, debugging was more complicated that I’m used to, e. g.,
>> autoconf’s config.log or similar output.
>>
>> ---
>>  compat/have_strcasestr.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/compat/have_strcasestr.c b/compat/have_strcasestr.c
>> index 3cd1838d..d52a62ec 100644
>> --- a/compat/have_strcasestr.c
>> +++ b/compat/have_strcasestr.c
>> @@ -1,5 +1,5 @@
>>  #define _GNU_SOURCE
>> -#include <strings.h>
>> +#include <string.h>
>
> Would it be better to include both strings.h and string.h, in
> case some (rare) cases it worked only when strings.h were included
> (or would that make the test fail in some cases then...?)

I don’t think it would cause any issues, but neither would I assume both
headers to be necessary somewhere.  Of course I haven’t tested it on Ye
Olde Unix With Its Special Own Taste on a workstation that pales in
comparison to my calculator, then again I assume they either (a) don’t
have strcasestr() anyway, or (b) fail to support notmuch because of some
other issues.

	--Thomas

> Tomi
>
>>  
>>  int
>>  main ()
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