Support reinstalling more packages (including base and template-haskell) with GHC >9.14 #10982
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
2 times, most recently
from
6cfbe6a to
e49a4b5
Compare
TeofilC
changed the title
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
2 times, most recently
from
ecb3159 to
dd63604
Compare
TeofilC
changed the title
TeofilC
changed the title
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
2 times, most recently
from
0bd8ca6 to
7b65354
Compare
TeofilC
commented
Jun 20, 2025
| -- We added a new field to compiler so we need to be careful | ||
| -- to make sure that it is always defined, | ||
| -- even if the test suite is being built with an older Cabal | ||
| #if MIN_VERSION_Cabal(3,15,0) |
There was a problem hiding this comment.
Any ideas how to do this better?
There was a problem hiding this comment.
Given that it's the test suite, I don't think it matters. For Cabal itself we'd usually use a Distribution.Compat module instead of raw CPP in the code.
TeofilC
changed the title
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
from
7b65354 to
c035d6f
Compare
TeofilC
changed the title
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
from
c035d6f to
3f1729d
Compare
In short, this change allows reinstalling packages like `base` and `template-haskell` with GHC >9.14, and it doesn't modify the behaviour of cabal-install with older versions of GHC for backwards-compatibility. cabal-install includes a hardcoded list of non-reinstallable packages. cabal-install will refuse to use a different version of these packages in a build plan unless the --allow-boot-library-installs flag is set. This list of packages is too pessimistic, and needlessly coupled to GHC. For instance, as of GHC-9.12, `base` and `template-haskell` can be "re-installed" without issue. This patch allows compilers to specify exactly which packages are wired-in and so should not be reinstalled. In the case of GHC-9.14+, this amounts to ghc-internal and ghc itself. If a compiler chooses to specify this information then it overrides the hardcoded non-reinstallable package list. Otherwise, it is still used for the sake of backwards compatibility. Note that this information comes in the form of unit-ids rather than package names. This patch extends the solver with constraints that force the use of a precise unit-id. The behaviour here is still somewhat pessimistic. In the future, we could further relax this restriction and only ban reinstalling these packafes when absolutely necessary, eg, only ban re-installing `ghc` if we are using plugins, etc. For the GHC change that added the interface to expose the unit-id of ghc-internal, see: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13297 Resolves #10087 Co-Authored-By: Matthew Pickering <[email protected]>
TeofilC
force-pushed
the
wip/teo-precise-unit-id
branch
from
3f1729d to
f087826
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Summary
This change allows reinstalling packages like
baseandtemplate-haskellwith GHC >9.14, and it doesn't modify the behaviourof cabal-install with older versions of GHC for backwards-compatibility.
Context
cabal-install includes a hardcoded list of non-reinstallable packages.
cabal-install will refuse to use a different version of these packages
in a build plan unless the --allow-boot-library-installs flag is set.
This list of packages is too pessimistic, and needlessly coupled to GHC.
For instance, as of GHC-9.12,
baseandtemplate-haskellcan be"re-installed" without issue.
Change
This patch allows compilers to specify exactly which packages are wired-in
and so should not be reinstalled.
In the case of GHC-9.14+, this amounts to ghc-internal and ghc itself.
If a compiler chooses to specify this information then it overrides the
hardcoded non-reinstallable package list. Otherwise, it is still used
for the sake of backwards compatibility.
Note that this information comes in the form of unit-ids rather than
package names. This patch extends the solver with constraints that force
the use of a precise unit-id.
The behaviour here is still somewhat pessimistic. In the future, we
could further relax this restriction and only ban reinstalling these
packafes when absolutely necessary, eg, only ban re-installing
ghcifwe are using plugins, etc.
For the GHC change that added the interface to expose the unit-id of
ghc-internal, see: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13297
Resolves #10087
Manual QA Notes
Build a compiler from this branch: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13297
and then confirm that when used with cabal from this branch it allows you to reinstall
template-haskellfor instance.For instance this is what happens if I try to build template-haskell with a released version of cabal-install:
cabal output
versus from this branch
cabal output
Include the following checklist in your PR:
significance: significantin the changelog file.