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| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2020-06-09 18:13:35 -0400 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-06-30 07:10:42 -0400 |
| commit | 71006532abb88a53df7c7e0b3a5e2c8af99a48d1 (patch) | |
| tree | d8874dbdd68ce911a83374dd6e241a80153553fc /testsuite/tests/rename/should_fail/T18240b.stderr | |
| parent | bfa5698b1ab0190820a2df19487d3d72d3a7924d (diff) | |
| download | haskell-71006532abb88a53df7c7e0b3a5e2c8af99a48d1.tar.gz | |
Reject nested foralls/contexts in instance types more consistently
GHC is very wishy-washy about rejecting instance declarations with
nested `forall`s or contexts that are surrounded by outermost
parentheses. This can even lead to some strange interactions with
`ScopedTypeVariables`, as demonstrated in #18240. This patch makes
GHC more consistently reject instance types with nested
`forall`s/contexts so as to prevent these strange interactions.
On the implementation side, this patch tweaks `splitLHsInstDeclTy`
and `getLHsInstDeclHead` to not look through parentheses, which can
be semantically significant. I've added a
`Note [No nested foralls or contexts in instance types]` in
`GHC.Hs.Type` to explain why. This also introduces a
`no_nested_foralls_contexts_err` function in `GHC.Rename.HsType` to
catch nested `forall`s/contexts in instance types. This function is
now used in `rnClsInstDecl` (for ordinary instance declarations) and
`rnSrcDerivDecl` (for standalone `deriving` declarations), the latter
of which fixes #18271.
On the documentation side, this adds a new
"Formal syntax for instance declaration types" section to the GHC
User's Guide that presents a BNF-style grammar for what is and isn't
allowed in instance types.
Fixes #18240. Fixes #18271.
Diffstat (limited to 'testsuite/tests/rename/should_fail/T18240b.stderr')
| -rw-r--r-- | testsuite/tests/rename/should_fail/T18240b.stderr | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/testsuite/tests/rename/should_fail/T18240b.stderr b/testsuite/tests/rename/should_fail/T18240b.stderr new file mode 100644 index 0000000000..330e5cc72f --- /dev/null +++ b/testsuite/tests/rename/should_fail/T18240b.stderr @@ -0,0 +1,24 @@ + +T18240b.hs:17:15: error: + ‘via’ type cannot contain nested ‘forall’s or contexts + In a deriving declaration + +T18240b.hs:18:24: error: + ‘via’ type cannot contain nested ‘forall’s or contexts + In a deriving declaration + +T18240b.hs:19:25: error: + ‘via’ type cannot contain nested ‘forall’s or contexts + In a deriving declaration + +T18240b.hs:26:24: error: + Derived class type cannot contain nested ‘forall’s or contexts + In the data type declaration for ‘Bar’ + +T18240b.hs:27:33: error: + Derived class type cannot contain nested ‘forall’s or contexts + In the data type declaration for ‘Bar’ + +T18240b.hs:28:34: error: + Derived class type cannot contain nested ‘forall’s or contexts + In the data type declaration for ‘Bar’ |