diff options
| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2019-04-30 11:28:41 -0400 |
|---|---|---|
| committer | Ömer Sinan Ağacan <omeragacan@gmail.com> | 2019-05-03 21:54:50 +0300 |
| commit | cc495d5777c01ef62129df15caacf87b0e430c6b (patch) | |
| tree | 98367d77415752a0b21e0bcb9a5cacd233de32c5 /testsuite/tests/ghci/scripts/T15872.script | |
| parent | 87bc954ab65aaf08b4f59cf46bd2916acd69ea73 (diff) | |
| download | haskell-cc495d5777c01ef62129df15caacf87b0e430c6b.tar.gz | |
Make equality constraints in kinds invisible
Issues #12102 and #15872 revealed something strange about the way GHC
handles equality constraints in kinds: it treats them as _visible_
arguments! This causes a litany of strange effects, from strange
error messages
(https://gitlab.haskell.org/ghc/ghc/issues/12102#note_169035)
to bizarre `Eq#`-related things leaking through to GHCi output, even
without any special flags enabled.
This patch is an attempt to contain some of this strangeness.
In particular:
* In `TcHsType.etaExpandAlgTyCon`, we propagate through the
`AnonArgFlag`s of any `Anon` binders. Previously, we were always
hard-coding them to `VisArg`, which meant that invisible binders
(like those whose kinds were equality constraint) would mistakenly
get flagged as visible.
* In `ToIface.toIfaceAppArgsX`, we previously assumed that the
argument to a `FunTy` always corresponding to a `Required`
argument. We now dispatch on the `FunTy`'s `AnonArgFlag` and map
`VisArg` to `Required` and `InvisArg` to `Inferred`. As a
consequence, the iface pretty-printer correctly recognizes that
equality coercions are inferred arguments, and as a result,
only displays them in `-fprint-explicit-kinds` is enabled.
* Speaking of iface pretty-printing, `Anon InvisArg` binders were
previously being pretty-printed like `T (a :: b ~ c)`, as if they
were required. This seemed inconsistent with other invisible
arguments (that are printed like `T @{d}`), so I decided to switch
this to `T @{a :: b ~ c}`.
Along the way, I also cleaned up a minor inaccuracy in the users'
guide section for constraints in kinds that was spotted in
https://gitlab.haskell.org/ghc/ghc/issues/12102#note_136220.
Fixes #12102 and #15872.
Diffstat (limited to 'testsuite/tests/ghci/scripts/T15872.script')
| -rw-r--r-- | testsuite/tests/ghci/scripts/T15872.script | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/testsuite/tests/ghci/scripts/T15872.script b/testsuite/tests/ghci/scripts/T15872.script new file mode 100644 index 0000000000..9a60bbd5f8 --- /dev/null +++ b/testsuite/tests/ghci/scripts/T15872.script @@ -0,0 +1,10 @@ +:l T15872 + +:t MkFun +:k Fun +:i Fun + +:set -fprint-explicit-kinds +:t MkFun +:k Fun +:i Fun |