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| author | Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io> | 2021-06-23 18:40:50 +0200 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-07-28 13:18:31 -0400 |
| commit | dabe61138a561e9a82961f81dbe276f9d909c1a7 (patch) | |
| tree | e5a5b8d361f61e1548ce247f21fcb560b0efe657 /docs | |
| parent | f325676956df650368c6ebbbbd53c69971551cd4 (diff) | |
| download | haskell-dabe61138a561e9a82961f81dbe276f9d909c1a7.tar.gz | |
Document DerivingVia unsafety (#19786)
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/exts/safe_haskell.rst | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/docs/users_guide/exts/safe_haskell.rst b/docs/users_guide/exts/safe_haskell.rst index 22508d5d7c..da62f093b2 100644 --- a/docs/users_guide/exts/safe_haskell.rst +++ b/docs/users_guide/exts/safe_haskell.rst @@ -273,8 +273,9 @@ Furthermore, we restrict the following features: site. This is a detailed restriction, please refer to :ref:`Safe Overlapping Instances <safe-overlapping-instances>` for details. -- :extension:`GeneralisedNewtypeDeriving` — GND is not allowed in the safe - language. This is due to the ability of it to violate module boundaries when +- :extension:`GeneralisedNewtypeDeriving` and :extension:`DerivingVia` + — GND and DerivingVia are not allowed in the safe language. + This is due to the ability of them to violate module boundaries when module authors forget to put nominal role annotations on their types as appropriate. For this reason, the ``Data.Coerce`` module is also considered unsafe. We are hoping to find a better solution here in the future. |