compiler: Rejects RULES whose LHS immediately fails to type-check
This is a bug fix for #24026 (closed): RULES that do not type check causing the compiler to crash when
-fdefer-type-errors
is used. There is a detailed conversation on #24026 (closed), but to
summarize there are two changes.
- A bug fix on
decomposeRuleLhs
that fix the fact that coercion variables where being ignored on decomposition. - A design choice to ignore rules that don't type-check early on. On normal programs
built with no special flags (see T24026b), type-checking fails with the expected error.
If for any reason, for example
-fdefer-type-errors
is used, and the compilation continues, rules that outright don't type check due to LHS failures will be ignored further, the user sees a warning, and GHC does not crash.
Please take a few moments to address the following points:
-
if your MR may break existing programs (e.g. touches base
or causes the compiler to reject programs), please describe the expected breakage and add the user-facing label. This will run ghc/head.hackage> to characterise the effect of your change on Hackage. -
ensure that your commits are either individually buildable or squashed -
ensure that your commit messages describe what they do (referring to tickets using #NNNN
syntax when appropriate) -
have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places. -
add a testcase to the testsuite. -
updates the users guide if applicable -
mentions new features in the release notes for the next release
If you have any questions don't hesitate to open your merge request and inquire
in a comment. If your patch isn't quite done yet please do add prefix your MR
title with WIP:
.
By default a minimal validation pipeline is run on each merge request, the full-ci label can be applied to perform additional validation checks if your MR affects a more unusual configuration.
Once your change is ready please remove the WIP:
tag and wait for review. If
no one has offered a review in a few days then please leave a comment mentioning
@triagers and apply the Blocked on Review label.