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Fix crash caused by discrepancy between type decl and boot file type decl #16127

Antoine Leblanc requested to merge nicuveo/ghc:issue16127 into master


This small patch fixes #16127 (closed), by following the recommendations outlined in #16127 (comment 496354).

Namely, in GHC.Tc.TyCl.checkValidTyCl, we now do a call to a new function checkTyConConsistentWithBoot, that attempts to find a matching definition in the boot info. If it does, it calls GHC.Tc.Module.checkBootDeclM, which errors if the two declarations do not match. This patch also adds a test that replicates the original issue in typecheck/T16127 (based on my small repro case).

I have checked that this test failed against release/ghc-9.8 with the "expected" panic.

Open questions

This is my first patch against GHC, and i have in consequence a few questions:

  • does checkTyConConsistentWithBoot match the naming convention? Should it be in snake case since it's not exported?
  • checkTyConConsistentWithBoot does not check whether we are currently compiling a boot file; i think that check isn't required, because if we are, then there will not be any boot info in the TcGblEnv, is that correct?
  • would it be possible to now remove the call to checkBootDeclM in Module.checkHiBootIface'.check_export, given that we should always have done that check by the time we reach that function? if it is possible: should we? or would it be better to leave the check as a precaution?

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