Fix embarrassing infinite loop in pprParendType
authorRyan Scott <ryan.gl.scott@gmail.com>
Mon, 3 Dec 2018 12:03:55 +0000 (07:03 -0500)
committerRyan Scott <ryan.gl.scott@gmail.com>
Mon, 3 Dec 2018 12:03:55 +0000 (07:03 -0500)
commit89d80921d9328499ffca9877e7dea540350be9c1
treeecb2c4b4577af6bf2ce373de42d6fe204c3cc855
parent2e6cc3d08f8439a2c0b6426e839d80072dbcda2c
Fix embarrassing infinite loop in pprParendType

Summary:
`pprParendType` was missing an explicit case for
`EqualityT`, which caused it to fall through to a catch-all case
that invokes `ppr`. But `ppr` itself does not have a case for a
partial application of `EqualityT`, so //it// falls back to
`pprParendType`, resulting in an infinite loop!

The fix is simple: add a case for `EqualityT` in `pprParendType`.
While I was in the neighborhood, I removed the catch-call case in
`pprParendType` to make this sort of mistake less likely to happen
in the future.

Test Plan: make test TEST=T15985

Reviewers: bgamari, monoidal, simonpj

Reviewed By: monoidal, simonpj

Subscribers: rwbarton, carter

GHC Trac Issues: #15985

Differential Revision: https://phabricator.haskell.org/D5403
libraries/template-haskell/Language/Haskell/TH/Ppr.hs
testsuite/tests/th/T15985.hs [new file with mode: 0644]
testsuite/tests/th/all.T