diff options
| -rw-r--r-- | hadrian/src/Rules/Libffi.hs | 37 |
1 files changed, 30 insertions, 7 deletions
diff --git a/hadrian/src/Rules/Libffi.hs b/hadrian/src/Rules/Libffi.hs index 44d6154fc2..9a251c0ebe 100644 --- a/hadrian/src/Rules/Libffi.hs +++ b/hadrian/src/Rules/Libffi.hs @@ -13,6 +13,35 @@ import Settings.Builders.Common import Target import Utilities +{- Note [Libffi indicating inputs] + +First see https://gitlab.haskell.org/ghc/ghc/wikis/Developing-Hadrian for an +explanation of "indicating input". Part of the definition is copied here for +your convenience: + + change in the vital output -> change in the indicating inputs + +In the case of building libffi `vital output = built libffi library files` and +we can consider the libffi archive file (i.e. the "libffi-tarballs/libffi*.tar.gz" +file) to be the only indicating input besides the build tools (e.g. make). +Note building libffi is split into a few rules, but we also expect that: + + no change in the archive file -> no change in the intermediate build artifacts + +and so the archive file is still a valid choice of indicating input for +all libffi rules. Hence we can get away with `need`ing only the archive file and +don't have to `need` intermediate build artifacts (besides those to trigger +dependant libffi rules i.e. to generate vital inputs as is noted on the wiki). +It is then safe to `trackAllow` the libffi build directory as is done in +`needLibfffiArchive`. + +A disadvantage to this approach is that changing the archive file forces a clean +build of libffi i.e. we cannot incrementally build libffi. This seems like a +performance issue, but is justified as building libffi is fast and the archive +file is rarely changed. + +-} + -- | Oracle question type. The oracle returns the list of dynamic -- libffi library file paths (all but one of which should be symlinks). newtype LibffiDynLibs = LibffiDynLibs Stage @@ -105,13 +134,7 @@ configureEnvironment stage = do , return . AddEnv "LDFLAGS" $ unwords ldFlags ++ " -w" ] -- Need the libffi archive and `trackAllow` all files in the build directory. --- As all libffi build files are derived from this archive, we can safely --- `trackAllow` the libffi build dir. I.e the archive file can be seen as a --- shallow dependency of the libffi build. This is much simpler than working out --- the dependencies of each rule (within the build dir). --- This means changing the archive file forces a clean build of libffi. This --- seems like a performance issue, but is justified as building libffi is fast --- and the archive file is rarely changed. +-- See [Libffi indicating inputs]. needLibfffiArchive :: FilePath -> Action FilePath needLibfffiArchive buildPath = do top <- topDirectory |