On Thu, Feb 18, 2016 at 6:43 AM, Herbert Valerio Riedel
On 2016-02-18 at 13:32:59 +0100, Andrey Mokhov wrote:
Interesting! In the new Shake-based build system we also need to automagically generate .hs files using Alex et al. My first implementation was slow but then I realised that it is possible to scan the source tree only once and remember where all .hs/.x/etc files are. This brought down the complexity from quadratic to linear in my case -- maybe this could be reused in cabal too?
This sounds very risky; are you suggesting to blindly traverse the hs-src-dirs *before* you even know what is searched for?
If so, this will cause problems; we're already seeing problems with this in the cabal nix-local-branch, which currently (it's a bug) recursively traverses the project folder for computing a source-hash over content that would not even make it into the source-dist...
There must be a better way to solve this...
I think what Andrey meant was, the first time we run the pre-processors, cache the locations of all the files that need to be pre-processed. On subsequent runs, we only need to check pre-processors the files in the cache. I've been thinking along these lines, too. This does break if you change what pre-processor is used to build a file, but I think that's OK because it happens so rarely. We would give the user a way to invalidate the cache, i.e. run the pre-processors manually by a `cabal pre-process` command. - Tom