Hi all,
So, any feedback for this? I still think it is a good idea to move the filetime
change check for a preprocessed file from preprocessFile to
mkSimplePreProcessor (both in Distribution.Simple.PreProcess). This gives
preprocessors the flexibility to define their own dependency tracking, and
would solve the problem with multiple input files generating a single Haskell
file. The change is quite simple, I could do it, but I'd like some feedback on
this.
In addition to this, we could add something like:
mkAdvancedPreProcessor :: (FilePath -> FilePath -> Verbosity -> IO (), FilePath
-> Verbosity -> IO [FilePath])
-> (FilePath, FilePath)
-> (FilePath, FilePath) -> Verbosity -> IO ()
which, in addition to the simplePreProcessor, should also provide a function
that returns all dependencies of a certain file. Then the file time change
check can also be done for the cases where multiple files generate a single
Haskell file. But that's maybe a less generic case which could be handled in
the preprocessor itself.
Regards,
Jeroen Bransen
Op 5 nov 2012, om 17:14 heeft Jeroen Bransen het volgende geschreven:
> With Distribution.Simple.PreProcess.PreProcessor we can add a custom
> preprocessor to our Haskell project. This works fine when there is a
> one-to-one mapping from other-source to Haskell-source file, but there is no
> good support for other types of preprocessors. For example, for our UUAGC [1]
> project we also have a cabal plugin [2], and we have the following situation.
>
> In general, an AG file (.ag) is preprocessed into a single .hs file with the
> same name. However, AG files can include other AG files so typically multiple
> AG files are preprocessed in a single .hs file. Let's say we have a X.ag
> which includes Y.ag and Z.ag, and from this X.hs should be generated. The
> first time that we build this is fine, as cabal sees that it can generate
> X.hs from X.ag and it calls the custom preprocessor. However, if we now edit
> Y.ag and rebuild, nothing will happen! Cabal will only check the file time of
> X.ag, which is not changed, so decides that X.hs does not need to be
> re-generated.
>
> Currently we have solved this in a quite ugly way by means of a buildHook
> that removes the generated .hs file whenever this file should be rebuild.
> Although this works it's of course not a good solution, but with the current
> setup I see no other way of doing this. I believe this should be a more
> common situation and it should actually be up to the preprocessor to decide
> whether or not to rebuild a file. I suggest the following change to
> Distribution.Simple.PreProcess.
>
> In the current version, the check for rebuilding is in preprocessFile, which
> simply compares file change times of input/output files. I suggest to remove
> that check from there and always call the preprocessor. It is then up to the
> preprocessor to decide not to preprocess a file when the generated file is
> already in place and nothing has changed. To handle the common situation
> where there is a one-to-one mapping, I suggest to move this check to
> mkSimplePreprocessor which is probably used by almost all preprocessors. In
> that way nothing changes for 'simple' preprocessors, but there is some extra
> flexibility for the cases like UUAGC.
>
> Regards,
> Jeroen Bransen
>
>
> [1] http://hackage.haskell.org/package/uuagc
> [2] http://hackage.haskell.org/package/uuagc-cabal
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