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Marge Bot pushed to branch master 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/d2bedffdc07b766f01dfcd4fc73a3859305814f3">d2bedffd</a></strong>
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<span> by Bartłomiej Cieślar </span> <i> at 2023-08-01T14:46:40-04:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 14px; color: #333238; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "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;'>Implementation of the Deprecated Instances proposal #575
This commit implements the ability to deprecate certain instances,
which causes the compiler to emit the desired deprecation message
whenever they are instantiated. For example:
module A where
class C t where
instance {-# DEPRECATED "dont use" #-} C Int where
module B where
import A
f :: C t => t
f = undefined
g :: Int
g = f -- "dont use" emitted here
The implementation is as follows:
- In the parser, we parse deprecations/warnings attached to instances:
instance {-# DEPRECATED "msg" #-} Show X
deriving instance {-# WARNING "msg2" #-} Eq Y
(Note that non-standalone deriving instance declarations do not support
this mechanism.)
- We store the resulting warning message in `ClsInstDecl` (respectively, `DerivDecl`).
In `GHC.Tc.TyCl.Instance.tcClsInstDecl` (respectively, `GHC.Tc.Deriv.Utils.newDerivClsInst`),
we pass on that information to `ClsInst` (and eventually store it in `IfaceClsInst` too).
- Finally, when we solve a constraint using such an instance, in
`GHC.Tc.Instance.Class.matchInstEnv`, we emit the appropriate warning
that was stored in `ClsInst`.
Note that we only emit a warning when the instance is used in a different module
than it is defined, which keeps the behaviour in line with the deprecation of
top-level identifiers.
Signed-off-by: Bartłomiej Cieślar <bcieslar2001@gmail.com>
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compiler/GHC/Core/InstEnv.hs
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compiler/GHC/Hs.hs
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compiler/GHC/Hs/Decls.hs
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compiler/GHC/Hs/ImpExp.hs
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compiler/GHC/Iface/Make.hs
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compiler/GHC/Iface/Syntax.hs
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compiler/GHC/IfaceToCore.hs
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compiler/GHC/Parser.y
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compiler/GHC/Parser/PostProcess.hs
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compiler/GHC/Rename/Env.hs
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compiler/GHC/Rename/Module.hs
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compiler/GHC/Rename/Names.hs
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compiler/GHC/Tc/Deriv.hs
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compiler/GHC/Tc/Deriv/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/Export.hs
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compiler/GHC/Tc/Instance/Class.hs
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compiler/GHC/Tc/Solver/Dict.hs
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compiler/GHC/Tc/TyCl/Instance.hs
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compiler/GHC/Tc/Types/Origin.hs
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compiler/GHC/Tc/Utils/Instantiate.hs
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compiler/GHC/ThToHs.hs
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compiler/GHC/Unit/Module/Warnings.hs
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docs/users_guide/exts/pragmas.rst
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testsuite/tests/haddock/should_compile_flag_haddock/T17544.stderr
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testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
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testsuite/tests/printer/Makefile
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testsuite/tests/printer/PprInstanceWarn.hs
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