Bug 312680 – [CMake] ccache hashes not portable across worktrees on Apple platforms

• Status: RESOLVED
• Resolution: FIXED
• Component: CMake

[Simon Lewis]

WebKitCCache.cmake sets CCACHE_SLOPPINESS via set(ENV{...}), and the mac
  presets set CCACHE_BASEDIR via the preset environment block. Both apply
  only to the cmake process — when ninja later spawns ccache, neither is
  set, so cache entries are stored with absolute paths and a second
  worktree of the same revision gets ~0% hits.

  WebKitCCache.cmake also unconditionally overwrites
  CMAKE_CXX_COMPILER_LAUNCHER, discarding any -D the user passed.

  On APPLE, generate ${CMAKE_BINARY_DIR}/ccache-launcher — a sh wrapper
  that exports CCACHE_BASEDIR=${CMAKE_SOURCE_DIR}, CCACHE_NOHASHDIR, and
  the sloppiness flags before exec'ing ccache — and point
  CMAKE_{C,CXX,ASM,OBJC,OBJCXX}_COMPILER_LAUNCHER at it. Skip the block
  entirely if CMAKE_CXX_COMPILER_LAUNCHER is already set.

  With the existing -fdebug-prefix-map in OptionsMac.cmake this gives 100%
  hits (99.8% direct) in a fresh worktree against a cache warmed elsewhere.

[Simon Lewis]

Pull request: https://github.com/WebKit/WebKit/pull/63043

[EWS]

Committed 311955@main (b36a53b5d2b8): <https://commits.webkit.org/311955@main>

Reviewed commits have been landed. Closing PR #63043 and removing active labels.