Require all the CFRunLoop headers together - #159
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AC_CHECK_HEADERS runs its action once per header it finds, so finding unistd.h alone was enough to reach AC_SEARCH_LIBS and define HAVE_CFRUNLOOP_SUPPORT. On a host without poll.h the result is a config.h carrying HAVE_CFRUNLOOP_SUPPORT 1 next to an undefined HAVE_POLL_H, and the build then fails in CFRunLoop.c on the missing header. Collect the results and decide once.
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August 14, 2026 02:02
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AC_CHECK_HEADERS runs its action once for every header it finds, not once when all of them are found. Finding unistd.h alone is therefore enough to reach AC_SEARCH_LIBS and define HAVE_CFRUNLOOP_SUPPORT.
On a host without poll.h the result is a config.h carrying HAVE_CFRUNLOOP_SUPPORT 1 next to an undefined HAVE_POLL_H. configure reports "checking for poll.h... no" and succeeds anyway, and the build then fails in CFRunLoop.c on the missing header.
The headers are collected first and the decision made once, so the define follows the check.
Found building on MSYS2 ucrt64, which has no poll.h. The same applies to any host missing one of the 5 headers.