Document GHC-44360 (#464)

* Document GHC-44360

* Apply suggestions from code review

Co-authored-by: David Thrane Christiansen <[email protected]>

---------

Co-authored-by: David Thrane Christiansen <[email protected]>

Author: BinderDavid

message-index/messages/GHC-44360/index.md

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+---
+title: Cannot import unsafe modules in Safe Haskell
+summary: Only safe modules can be imported in modules which are declared safe
+severity: error
+introduced: 9.6.1
+---
+
+GHC implements the `SafeHaskell` extension which allows programmers to restrict modules to a specific subset which is considered safe and does not contain loopholes such as `unsafePerformIO`. More details are available in [the GHC User's Guide](https://downloads.haskell.org/ghc/latest/docs/users_guide/exts/safe_haskell.html).
+In order to uphold the guarantees of Safe Haskell, GHC does not allow modules which are declared safe to import unsafe modules.

message-index/messages/GHC-44360/unsafe-import/after/UnsafeImport.hs

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+
+module UnsafeImport where
+
+import Unsafe.Coerce

message-index/messages/GHC-44360/unsafe-import/before/UnsafeImport.hs

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+{-# LANGUAGE Safe #-}
+module UnsafeImport where
+
+import Unsafe.Coerce

message-index/messages/GHC-44360/unsafe-import/index.md

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+---
+title: Safe module tries to import Unsafe.Coerce
+---
+
+This module tries to import the module `Unsafe.Coerce`, even though the module is declared to be safe.
+In order to use an unsafe module such as `Unsafe.Coerce`, the annotation which declares the module to be safe has to be removed.
+
+```
+messages/GHC-44360/unsafe-import/before/UnsafeImport.hs:4:1: error: [GHC-44360]
+    Unsafe.Coerce: Can't be safely imported!
+    The module itself isn't safe.
+  |
+4 | import Unsafe.Coerce
+  | ^^^^^^^^^^^^^^^^^^^^
+```