1. 07 Dec, 2012 1 commit
    • Brad King's avatar
      Add policy CMP0019 to skip include/link variable re-expansion · 711b63f7
      Brad King authored
      Historically CMake has always expanded ${} variable references in the
      values given to include_directories(), link_directories(), and
      link_libraries().  This has been unnecessary since general ${}
      evaluation syntax was added to the language a LONG time ago, but has
      remained for compatibility with VERY early CMake versions.
      
      For a long time the re-expansion was a lightweight operation because it
      was only processed once at the directory level and the fast-path of
      cmMakefile::ExpandVariablesInString was usually taken because values did
      not have any '$' in them.  Then commit d899eb71 (Call
      ExpandVariablesInString for each target's INCLUDE_DIRECTORIES,
      2012-02-22) made the operation a bit heavier because the expansion is
      now needed on a per-target basis.  In the future we will support
      generator expressions in INCLUDE_DIRECTORIES with $<> syntax, so the
      fast-path in cmMakefile::ExpandVariablesInString will no longer be taken
      and re-expansion will be very expensive.
      
      Add policy CMP0019 to skip the re-expansion altogether in NEW behavior.
      In OLD behavior perform the expansion but improve the fast-path
      heuristic to match ${} but not $<>.  If the policy is not set then warn
      if expansion actually does anything.  We expect this to be encountered
      very rarely in practice.
      711b63f7