1. 13 Sep, 2018 2 commits
  2. 17 Jul, 2018 1 commit
    • Thomas Haller's avatar
      build: create "config-extra.h" header instead of passing directory variables via CFLAGS · a75ab799
      Thomas Haller authored
      1) the command line gets shorter. I frequently run `make V=1` to see
         the command line arguments for the compiler, and there is a lot
         of noise.
      
      2) define each of these variables at one place. This makes it easy
         to verify that for all compilation units, a particular
         define has the same value. Previously that was not obvious or
         even not the case (see commit e5d1a713
         and commit d63cf1ef).
         The point is to avoid redundancy.
      
      3) not all compilation units need all defines. In fact, most modules
         would only need a few of these defines. We aimed to pass the necessary
         minium of defines to each compilation unit, but that was non-obvious
         to get right and often we set a define that wasn't used. See for example
         "src_settings_plugins_ibft_cppflags" which needlessly had "-DSYSCONFDIR".
         This question is now entirely avoided by just defining all variables in
         a header. We don't care to find the minimum, because every component
         gets anyway all defines from the header.
      
      4) this also avoids the situation, where a module that previously did
         not use a particular define gets modified to require it. Previously,
         that would have required to identify the missing define, and add
         it to the CFLAGS of the complation unit. Since every compilation
         now includes "config-extra.h", all defines are available everywhere.
      
      5) the fact that each define is now available in all compilation units
         could be perceived as a downside. But it isn't, because these defines
         should have a unique name and one specific value. Defining the same
         name with different values, or refer to the same value by different
         names is a bug, not a desirable feature. Since these defines should
         be unique accross the entire tree, there is no problem in providing
         them to every compilation unit.
      
      6) the reason why we generate "config-extra.h" this way, instead of using
         AC_DEFINE() in configure.ac, is due to the particular handling of
         autoconf for directory variables. See [1].
         With meson, it would be trivial to put them into "config.h.meson".
         While that is not easy with autoconf, the "config-extra.h" workaround
         seems still preferable to me.
      
      [1] https://www.gnu.org/software/autoconf/manual/autoconf-2.63/html_node/Installation-Directory-Variables.html
      a75ab799