diff options
| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2020-11-13 10:56:20 -0500 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-11-15 03:36:21 -0500 |
| commit | 645444af9eb185684c750c95e4740d301352b2b9 (patch) | |
| tree | 6e2e1136560d7e2acf1075c3974a65c18ae10512 /compiler/GHC/Tc/Utils/Backpack.hs | |
| parent | d61adb3dace8f52e21f302989182145a0efa103f (diff) | |
| download | haskell-645444af9eb185684c750c95e4740d301352b2b9.tar.gz | |
Use tcSplitForAllInvisTyVars (not tcSplitForAllTyVars) in more places
The use of `tcSplitForAllTyVars` in `tcDataFamInstHeader` was the immediate
cause of #18939, and replacing it with a new `tcSplitForAllInvisTyVars`
function (which behaves like `tcSplitForAllTyVars` but only splits invisible
type variables) fixes the issue. However, this led me to realize that _most_
uses of `tcSplitForAllTyVars` in GHC really ought to be
`tcSplitForAllInvisTyVars` instead. While I was in town, I opted to replace
most uses of `tcSplitForAllTys` with `tcSplitForAllTysInvis` to reduce the
likelihood of such bugs in the future.
I say "most uses" above since there is one notable place where we _do_ want
to use `tcSplitForAllTyVars`: in `GHC.Tc.Validity.forAllTyErr`, which produces
the "`Illegal polymorphic type`" error message if you try to use a higher-rank
`forall` without having `RankNTypes` enabled. Here, we really do want to split
all `forall`s, not just invisible ones, or we run the risk of giving an
inaccurate error message in the newly added `T18939_Fail` test case.
I debated at some length whether I wanted to name the new function
`tcSplitForAllInvisTyVars` or `tcSplitForAllTyVarsInvisible`, but in the end,
I decided that I liked the former better. For consistency's sake, I opted to
rename the existing `splitPiTysInvisible` and `splitPiTysInvisibleN` functions
to `splitInvisPiTys` and `splitPiTysInvisN`, respectively, so that they use the
same naming convention. As a consequence, this ended up requiring a `haddock`
submodule bump.
Fixes #18939.
Diffstat (limited to 'compiler/GHC/Tc/Utils/Backpack.hs')
| -rw-r--r-- | compiler/GHC/Tc/Utils/Backpack.hs | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/compiler/GHC/Tc/Utils/Backpack.hs b/compiler/GHC/Tc/Utils/Backpack.hs index de114c3817..6214434fce 100644 --- a/compiler/GHC/Tc/Utils/Backpack.hs +++ b/compiler/GHC/Tc/Utils/Backpack.hs @@ -223,8 +223,8 @@ check_inst sig_inst = do skol_info = InstSkol -- Based off of tcSplitDFunTy (tvs, theta, pred) = - case tcSplitForAllTyVars ty of { (tvs, rho) -> - case splitFunTys rho of { (theta, pred) -> + case tcSplitForAllInvisTyVars ty of { (tvs, rho) -> + case splitFunTys rho of { (theta, pred) -> (tvs, theta, pred) }} origin = InstProvidedOrigin (tcg_semantic_mod tcg_env) sig_inst (skol_subst, tvs_skols) <- tcInstSkolTyVars tvs -- Skolemize |