Compiling with optimisations

[jaror]

I posted this related topic a while ago:

TIL: ghc-options: -O2 is a questionable practice

While browsing issues in the cabal github repository I encountered this comment by Oleg Grengrus: [We] consider ghc-options: -O2 (any -O flag) to be at the very least questionable practice. In cabal.project you can have optimization: 2 for all local, or per package (also non-local) The core idea is that optimizations could be configured for all packages in an uniform way, without investigating if there’s some dev, devel or fast flag. Also as a bonus, changing optimization level (also poss…

So I’d say the optimization field in cabal.project files should be preferred over -O in ghc-options. To enable “-O2” optimizations for all local and non-local dependencies I think you’d have to make a cabal.project file with these contents (note that all packages are already built with optimization level 1 by default):

packages: .
optimization: 2
package *
  optimization: 2

(The difference between non-local and local is essentially whether it is from Hackage or directly from your machine.)

I think the remark about caching is only for local packages and blowing away the old build products should be as easy as running cabal clean. For packages in the cabal store, cabal already tracks configuration options which I think includes optimization level to choose the right built package to use.