haskell.compiler.ghcjs: remove at 8.10.7 (#422342)

Author: sternenseemann

doc/release-notes/rl-2511.section.md

@@ -46,6 +46,16 @@
 
 - `conduwuit` was removed due to upstream ceasing development and deleting their repository. For existing data, a migration to `matrix-conduit`, `matrix-continuwuity` or `matrix-tuwunel` may be possible.
 
+- The GHCJS 8.10.7, exposed via `haskell.compiler.ghcjs` and `haskell.compiler.ghcjs810`, has been removed. Downstream users should migrate their projects to the new JavaScript backend of GHC proper which can be used via `pkgsCross.ghcjs` from Nixpkgs. Haskell packaging code, like `haskellPackages.mkDerivation`, `ghcWithPackages` and `hoogleWithPackages`, also no longer supports GHCJS.
+
+- The `ghcInfo` and `controlPhases` functions have been removed from `haskell.lib.compose` and `haskell.lib`. They were unused and would return incorrect results.
+
+  - Instead of using `controlPhases`, the `doCheck` attribute of derivations can be accessed which is more accurate. `doBenchmark` can't be introspected at the moment.
+  - To detect cross compilation, the relevant platforms exposed by `stdenv` should be compared instead of using `ghcInfo`.
+  - Nixpkgs no longer packages any `ghcjs` compiler.
+  - To find a suitable `nativeGhc`, `buildHaskellPackages` should be used. `ghcInfo` would use `ghc.bootPkgs.ghc` if cross compiling,
+    and the given `ghc` otherwise. This approach is not recommended since it results in mismatched GHC versions.
+
 - `gnome-keyring` no longer ships with an SSH agent anymore because it has been deprecated upstream. You should use `gcr_4` instead, which provides the same features. More information on why this was done can be found on [the relevant GCR upstream PR](https://gitlab.gnome.org/GNOME/gcr/-/merge_requests/67).
 
 - `stdenv.mkDerivation` and other derivation builders that use it no longer allow the value of `env` to be anything but an attribute set, for the purpose of setting environment variables that are available to the [builder](https://nix.dev/manual/nix/latest/store/derivation/#builder) process. An environment variable called `env` can still be provided by means of `mkDerivation { env.env = ...; }`, though we recommend to use a more specific name than "env".