GHC 8.10.4 (#1033)

* Adds GHC 8.10.4 support

* Drops GHC 8.8.3, 8.10.2 and 8.10.3 from CI

* Adds warning to encourage people to use less buggy ghc

Author: hamishmack

ci.nix

@@ -27,14 +27,12 @@
       ghc865 = true;
       ghc884 = false; # Just included because the native version is needed at eval time
     } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
-      ghc883 = false;
       ghc884 = true;
-      ghc8102 = false;
-      ghc8103 = true;
+      ghc8104 = true;
       ghc810220201118 = false;
     } // nixpkgs.lib.optionalAttrs (nixpkgsName == "unstable") {
       ghc884 = true;
-      ghc8103 = true;
+      ghc8104 = true;
     });
   systems = nixpkgs: nixpkgs.lib.filterAttrs (_: v: builtins.elem v supportedSystems) {
     # I wanted to take these from 'lib.systems.examples', but apparently there isn't one for linux!
@@ -48,7 +46,7 @@
     in lib.optionalAttrs (nixpkgsName == "R2009" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
     inherit (lib.systems.examples) ghcjs;
   } // lib.optionalAttrs (system == "x86_64-linux" && (
-         (nixpkgsName == "R2009" && __elem compiler-nix-name ["ghc8101" "ghc8102" "ghc8103" "ghc810220201118"])
+         (nixpkgsName == "R2009" && __elem compiler-nix-name ["ghc8101" "ghc8102" "ghc8103" "ghc8104" "ghc810220201118"])
       || (nixpkgsName == "R2003" && __elem compiler-nix-name ["ghc865"]))) {
     # Windows cross compilation is currently broken on macOS
     inherit (lib.systems.examples) mingwW64;

docs/reference/supported-ghc-versions.md

@@ -5,7 +5,7 @@ The following GHC versions are defined in `haskell.nix` (i.e. there is a derivat
 - 8.4.4
 - 8.6.{1,2,3,4,5}
 - 8.8.{1,2,3,4}
-- 8.10.{1,2,3}
+- 8.10.{1,2,3,4}
 
 The following table shows the nixpkgs/GHC versions which are built by CI, and which of those are tested.
 If you use a combination of nixpkgs version and GHC version which is in this table, you should get cache hits from our cache.
@@ -15,13 +15,11 @@ The "nixpkgs versions" refer to the versions that `haskell.nix` provides; if you
 |------------------|-------------|---------|
 | 20.03            | 8.6.5       | Y       |
 | 20.09            | 8.6.5       | Y       |
-| 20.09            | 8.8.3       | N       |
 | 20.09            | 8.8.4       | Y       |
-| 20.09            | 8.10.2      | N       |
-| 20.09            | 8.10.3      | Y       |
+| 20.09            | 8.10.4      | Y       |
 | nixpkgs-unstable | 8.6.5       | Y       |
 | nixpkgs-unstable | 8.8.4       | Y       |
-| nixpkgs-unstable | 8.10.3      | Y       |
+| nixpkgs-unstable | 8.10.4      | Y       |
 
 See [ci.nix](https://github.com/input-output-hk/haskell.nix/blob/master/ci.nix) for the source of truth about what is built and tested.