Detect header changes in build system

[nikic]

make performs incremental compilation, i.e. it will only rebuild files that have changed. However, apart from few exceptions, our build system currently does not take any dependencies into account. The two most common issues are:

• If a header is changed, all C files including that header may need to be rebuilt. This may be fixed by running make clean.
• If the build configuration changes (e.g. one of the config.m4 files), then configure needs to be rerun. This may be fixed by running ./buildconf && ./config.nice && make clean.

The first issue is more common than the second. It would be great if we would at least detect header changes automatically. This should be possible based on the -M family of compiler flags, but I'm not familiar with how these need to be integrated.

[johannes]

One could re-evaluate the build system in full an use something else. 10 years ago we had a summer of code project for CMake, this went nowhere mostly for "meh, why change?" reasons (and probably due to coming from Windows folks who want to unify on a single build system instead of having that fancy JavaScript system) http://svn.php.net/viewvc/php/cmake/ CMake+Ninja is quite acceptable these days.

Might also solve "configure is so slow" issues.

[nikic]

I'd certainly be in favor of a switch to cmake, but don't have much hope it'll actually happen. Migrating php-src itself would be hard enough (though the pkg-config migration in 7.4 has probably made this a bit easier), and then one still has to deal with 3rd party extensions.

[johannes]

For third party extensions we can keep phpize around for a while and provide a find_php.cmake with some helper macros for modern things ...

But yes, a big project requiring somebody with time and energy.

[nikic]

This has been implemented in php/php-src#6693.