| name | update-cabal-toolchain |
| description | Update mtg-pure's cabal dependency bounds and source to build on a newer GHC/toolchain than it was pinned to. Use when cabal build fails with dependency version-bound conflicts, "unknown package", Cabal-8011 configure errors, or newly-fatal GHC warnings after a compiler upgrade. Covers bumping build-depends to the boot-library versions and the recurring GHC-9.10 / base-4.20 source fixes. |
Update mtg-pure for a newer toolchain
The cabal file was originally pinned to a GHC 9.4-era world (base ^>=4.17).
When the installed GHC is newer (currently GHC 9.10.3 / base 4.20), the
solver and -Wall -Werror reject the old pins and stricter warnings. This skill
is the migration playbook. Build via the build skill; those environment
presteps (cabal update, sh on PATH for configure, regenerating ToObjectN)
are assumed here.
1. Bump build-depends bounds to the active GHC's boot libraries
The tight ^>= upper caps block the versions that ship with the new GHC. Query
the actual versions and set the caret lower bound to match, keeping the caret
style (do not convert to bare >= — the author prefers bounded deps):
$env:Path = "C:\ghcup\bin;" + $env:Path
foreach ($p in 'base','array','binary','bytestring','containers','filepath',
'mtl','template-haskell','time','transformers') { ghc-pkg latest $p }
Then edit ghc-options's neighbor block in
mtg-pure.cabal. For GHC 9.10 the known-good set is:
| Package | Bound |
|---|
base | ^>=4.20 |
array | ^>=0.5.8.0 |
binary | ^>=0.8.9.0 |
bytestring | ^>=0.12.2.0 |
containers | ^>=0.7 |
filepath | ^>=1.5.4.0 |
mtl | ^>=2.3.1 |
template-haskell | ^>=2.22.0.0 |
time | ^>=1.12.2 |
transformers | ^>=0.6.1.1 |
Non-boot Hackage deps whose old caps also blocked 9.10: aeson ^>=2.2,
ansi-terminal ^>=1.1. Everything else (async, colour, directory,
dlist, http-conduit, JuicyPixels, parsec, process, random, split,
Stream, vector, …) already allowed 9.10-era versions — leave those alone.
Also drop any accidental duplicate lines (there was a repeated parsec).
If cabal build says unknown package: <x>, the Hackage index is empty →
cabal update (this is an environment issue, not a bounds issue).
2. Fix new build errors (if applicable). Do not try to hide the errors.
Fix, rebuild, read the next error, repeat — GHC surfaces a handful at a time
because the build aborts modules in parallel.
3. Regenerate generated code if the object machinery changed
If you touched the OT/ObjectN types (or the generated tree is missing/stale),
re-run the generator — see the regen-object-code skill. A boot-only
runghc CodeGen.hs from src/ is enough; fourmolu is optional.
Gotchas
cabal repl --repl-options=-fobject-code recompiles everything with
[Flags changed] if those flags differ from the build. For a plain REPL use
cabal repl with no extra flags to reuse the build artifacts.- Log with
Out-File -Encoding utf8; the PowerShell default UTF-16 reads back as
spaced-out garbage.
- After a successful migration, update the stale "no toolchain" claims in
docs/ (working-without-builds.md, README, orientation) and the
mtg-pure-no-builds memory if they haven't been already.
