haskell/aeson

warning: [GHC-90584] [-Wderiving-typeable]

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#1,177 opened on Jun 22, 2026

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good first issueversioning level: minor/non-breaking addition

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Description

GHC 9.14.1 issues warnings as following:

src/Data/Aeson/Key.hs:45:13: warning: [GHC-90584] [-Wderiving-typeable]
    * Deriving `Typeable' has no effect: all types now auto-derive Typeable
    * In the newtype declaration for `Key'
   |
45 |   deriving (Typeable, Data)
   |             ^^^^^^^^

https://errors.haskell.org/messages/GHC-90584/

https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Key.hs#L44-L45 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/KeyMap.hs#L142-L144 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Types/Internal.hs#L114-L115 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Types/Internal.hs#L118-L126 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Types/Internal.hs#L365-L372 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Types/Internal.hs#L497-L508 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Encoding/Internal.hs#L78-L85 https://github.com/haskell/aeson/blob/10c23ba00bd96a747685706c60b90ddd52a92f9e/src/Data/Aeson/Encoding/Internal.hs#L122-L131

Contributor guide

Research direction
Remove the deriving Typeable from the newtype and data declarations in the listed files.
Tech stack
None
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
1
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
HaskellGHC
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80