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Created by Andreas Abel@abel

panic: `Prelude.chr: bad argument` in GHC < 8.10 when stale interface is present

Summary

With .hi and .o left over from compilation with GHC-9.0.1, older GHC versions panic, e.g.:

$ ghc-8.8.4 AbsTest.hs
ghc: panic! (the 'impossible' happened)
  (GHC version 8.8.4 for x86_64-apple-darwin):
	Prelude.chr: bad argument: 4043309068

I tested 7.6 - 8.8.

Steps to reproduce

I can reproduce the issue with this script:

# Generate *.o *.hi that trip up older GHCs
ghc-9.0.1 Test.hs

# Produce panics in older GHCs
ghc-7.6.3 Test.hs
ghc-7.8.4 Test.hs
ghc-7.10.3 Test.hs
ghc-8.0.2 Test.hs
ghc-8.2.2 Test.hs
ghc-8.4.4 Test.hs
ghc-8.6.4 Test.hs
ghc-8.8.4 Test.hs

# From 8.10, this seems fixed
ghc-8.10.4 Test.hs
ghc-9.0.1 Test.hs

The source file Test.hs is an empty module:

module Test where

Expected behavior

What do you expect the reproducer described above to do?

No panic, but ignore stale products and recompile.

Environment

  • GHC version used: 7.6 - 8.8
  • Operating System: macOS

Related issues

Edited by Andreas Abel
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