One freeze-file per GHC version

[andreasabel]

There should be one freeze file per GHC version (like there is a build directory per GHC version in v2-cabal). Otherwise, freeze does not work as expected in a multi-GHC environment. I expect cabal v2-freeze -w ghc-x.y.z to work analogously to cabal v2-build -w ghc-x.y.z.

Currently there is a single cabal.project.freeze.

See also #2245.

[phadej]

I agree, freeze file makes mostly sense for single compiler only.

This is challenging. Freeze file is just a convention, it's not "special". It is an unrestricted appendix to cabal.project (hardcoded like cabal.project.include). So this feature request is not much different then asking to select different cabal.project files based on --with-compiler flag. This is even more challenging then builddir in cabal.project (#5271), but the reason is the same: compiler can be set in cabal.project with with-compiler: ....

I'm afraid that project configuration have to be reworked in some non-trivial way to support this.

EDIT: an important constraint is that project configuration can be read in <10ms, to guarantee interactive-fast responses for no-build-op operations (e.g. cabal list-bin). Otherwise people (including myself) will loudly complain about why cabal-install become slow.

[fgaz]

We could partially get there by adding a --freeze-file flag that works like the --project-file one

[fgaz]

By the way, the freeze file can be changed, just together with the main project file: --project-file affects all kinds of project files together, so using --project-file=cabal.project.ghc-x.y would make cabal pick up a cabal.project.ghc-x.y.freeze (and cabal.project.ghc-x.y.local) file.

This might be a nuisance when the project file is big and has to be copied multiple times, but it works, and symlinks can solve the duplication

[jneira]

only want to note that symlinking in windows is not reliable in general

[gbaz]

I think that explicit includes (discussed on related ticket) plus allowing includes in conditional stanzas would give a way to do this, albeit not the most seamless ux for it.

[andreabedini]

After getting explicit includes and cabal freeze -w; is there anything left to this ticket or it can it be close?

[michaelpj]

Just wanted to note that it's not enough to have one per compiler version, it can also vary per platform. So in principle you need one per compiler-version/platform combination.