ApplicativeDo causes the wrong line to be reported in non-exhaustive pattern error messages

Summary

With ApplicativeDo on, some programs (such as a test that crashed yesterday) that are Applicative in structure can get desugared to Applicative, and the source of non-exhaustive pattern error messages gets mixed up.

Steps to reproduce

Save this in Test.hs:

main = do
  let x = ()
  res2 <- pure ()
  ~(Just res1) <- seq x (pure $ Nothing @())
  print res1
  print res2
  pure ()

Then:

[nix-shell:~/dev/nixpkgs]$ runhaskell Test.hs
Test.hs: Test.hs:4:3-44: Non-exhaustive patterns in Just res1


[nix-shell:~/dev/nixpkgs]$ runhaskell -XApplicativeDo Test.hs
Test.hs: Test.hs:2:3-12: Non-exhaustive patterns in Just res1

Line 2 is incorrectly reported as the cause in the case of ApplicativeDo (which in the case of the test I was hacking on, was actually another irrefutable pattern that was actually fine, so I was absolutely baffled).

Expected behavior

Both cases of -XApplicativeDo and not should report the same error location.

Environment

• GHC version used: 9.4.3

Optional:

• Operating System: macOS
• System Architecture: aarch64