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<h3 style="margin-top: 20px; margin-bottom: 10px;">
Andrei Borzenkov pushed to branch wip/sand-witch/pattern-@a-binders at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
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Commits:
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<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/532c915d2b462780e1811ac31c3b78cdca7328a3">532c915d</a></strong>
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<span> by Andrei Borzenkov </span> <i> at 2023-06-26T22:52:48+04:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.875rem; color: #333238; position: relative; font-family: var(--default-mono-font, "Menlo"),"DejaVu Sans Mono","Liberation Mono","Consolas","Ubuntu Mono","Courier New","andale mono","lucida console",monospace; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dcdcde;'>Draft: Type patterns (22478, 18986)
Improved name resolution and type checking of type patterns in constructors:
1. HsTyPat: a new dedicated data type that represents type patterns in
HsConPatDetails instead of reusing HsPatSigType
2. rnHsTyPat: a new function that renames a type
pattern and collects its binders into three groups:
- explicitly bound type variables, excluding locally bound
variables
- implicitly bound type variables from kind signatures
(only if ScopedTypeVariables are enabled)
- named wildcards (only from kind signatures)
2a. rnHsPatSigTypeBindingVars: removed in favour of rnHsTyPat
2b. rnImplcitTvBndrs: removed because no longer needed
3. collect_pat: updated to collect type variable binders from type patterns
(this means that types and terms use the same infrastructure to detect
conflicting bindings, unused variables and name shadowing)
3a. CollVarTyVarBinders: a new CollectFlag constructor that enables
collection of type variables
4. tcHsTyPat: a new function that typechecks type patterns, capable of
handling polymorphic kinds.
See Note [Type patterns: binders and unifiers]
Examples of code that is now accepted:
f = \(P @a) -> \(P @a) -> ... -- triggers -Wname-shadowing
g :: forall a. Proxy a -> ...
g (P @a) = ... -- also triggers -Wname-shadowing
h (P @($(TH.varT (TH.mkName "t")))) = ...
-- t is bound at splice time
j (P @(a :: (x,x))) = ... -- (x,x) is no longer rejected
data T where
MkT :: forall (f :: forall k. k -> Type).
f Int -> f Maybe -> T
k :: T -> ()
k (MkT @f (x :: f Int) (y :: f Maybe)) = ()
-- f :: forall k. k -> Type
Examples of code that is rejected with better error messages:
f (Left @a @a _) = ...
-- new message:
-- • Conflicting definitions for ‘a’
-- Bound at: Test.hs:1:11
-- Test.hs:1:14
Examples of code that is now rejected:
{-# OPTIONS_GHC -Werror=unused-matches #-}
f (P @a) = ()
-- Defined but not used: type variable ‘a’
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<a href="#9f00edfedb0f969865b049a78de3866545b4a60b">
compiler/GHC/Hs/Instances.hs
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compiler/GHC/Hs/Pat.hs
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compiler/GHC/Hs/Type.hs
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compiler/GHC/Hs/Utils.hs
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compiler/GHC/HsToCore/Quote.hs
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compiler/GHC/Iface/Ext/Ast.hs
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compiler/GHC/Parser/PostProcess.hs
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compiler/GHC/Parser/Types.hs
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compiler/GHC/Rename/HsType.hs
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compiler/GHC/Rename/Pat.hs
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compiler/GHC/Rename/Splice.hs
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compiler/GHC/Rename/Splice.hs-boot
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compiler/GHC/Rename/Utils.hs
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compiler/GHC/Tc/Errors/Ppr.hs
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compiler/GHC/Tc/Errors/Types.hs
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compiler/GHC/Tc/Gen/HsType.hs
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compiler/GHC/Tc/Gen/Pat.hs
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compiler/GHC/Tc/Utils/TcMType.hs
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compiler/GHC/ThToHs.hs
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compiler/GHC/Types/Error/Codes.hs
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compiler/GHC/Types/Name/Reader.hs
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compiler/Language/Haskell/Syntax/Extension.hs
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compiler/Language/Haskell/Syntax/Pat.hs
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compiler/Language/Haskell/Syntax/Type.hs
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testsuite/tests/gadt/T18191.stderr
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testsuite/tests/rename/should_compile/all.T
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testsuite/tests/rename/should_fail/T22478b.hs
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testsuite/tests/rename/should_fail/T22478d.hs
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