Drop GHC <9.6 from CI

Author: hamishmack

changelog.md

@@ -1,6 +1,15 @@
 This file contains a summary of changes to Haskell.nix and `nix-tools`
 that will impact users.
 
+## Jan 29, 2024
+
+Removed GHC <9.6 from CI.
+
+The latest `nixpkgs-unstable` cause problems with
+  * GHC 8.10.7
+  * GHC 9.6.6 mingwW64 (ucrt64 works still as does mingwW64
+    with newer GHC versions)
+
 ## Sep 17, 2024
 
 Cabal projects now use the more granular Unit IDs from plan.json

ci.nix

@@ -18,11 +18,6 @@
 
   # short names for nixpkgs versions
   nixpkgsVersions = {
-    "R2205" = inputs.nixpkgs-2205;
-    "R2211" = inputs.nixpkgs-2211;
-    "R2305" = inputs.nixpkgs-2305;
-    "R2311" = inputs.nixpkgs-2311;
-    "R2405" = inputs.nixpkgs-2405;
     "R2411" = inputs.nixpkgs-2411;
     "unstable" = inputs.nixpkgs-unstable;
   };
@@ -63,10 +58,9 @@
       # from here (so that is no longer cached) also remove ./materialized/ghcXXX.
       # Update supported-ghc-versions.md to reflect any changes made here.
       nixpkgs.lib.optionalAttrs (nixpkgsName == "R2411") {
-        ghc92 = false;
-        ghc94 = false;
-        ghc96 = false;
-        ghc98 = false;
+        # TODO perhaps these
+        # ghc96 = false;
+        # ghc98 = false;
       } // nixpkgs.lib.optionalAttrs (nixpkgsName == "unstable") {
         ghc96 = true;
         ghc98 = true;

docs/reference/supported-ghc-versions.md

@@ -2,13 +2,14 @@
 
 The following GHC versions are defined in `haskell.nix` (there is a derivation
 for each, though not all are cached or tested by CI):
-- 8.4.4
-- 8.6.{1,2,3,4,5}
-- 8.8.{1,2,3,4}
-- 8.10.{1,2,3,4,5}
-- 9.0.1
-- 9.2.1
-- 9.2.2
+
+- 9.6.6 (TH is broken in mingwW64, but ucrt64 works)
+- 9.8.4
+- 9.10.1
+- 9.12.1
+
+8.10.7 may still work with older nixpkgs versions, but is broken for
+nixpkgs-unstable.
 
 The following table shows the Nixpkgs/GHC versions which are built/cached, and
 which of those are further tested.  If you use a combination of Nixpkgs version
@@ -21,13 +22,10 @@ really should use an instance of Nixpkgs provided by `haskell.nix` itself.
 
 | Nixpkgs version  | Nixpkgs pinning    | GHC version | `compiler-nix-name`   | Tested in CI? |
 |------------------|--------------------|-------------|-----------------------|---------------|
-| 22.05            | `nixpkgs-2205`     | 8.6.5       | `ghc865`              | No            |
-| 22.05            | `nixpkgs-2205`     | 8.10.7      | `ghc8107`             | No            |
-| unstable         | `nixpkgs-unstable` | 8.6.5       | `ghc865`              | No            |
-| unstable         | `nixpkgs-unstable` | 8.8.4       | `ghc884`              | No            |
-| unstable         | `nixpkgs-unstable` | 8.10.7      | `ghc8107`             | Yes           |
-| unstable         | `nixpkgs-unstable` | 9.0.2       | `ghc902`              | No            |
-| unstable         | `nixpkgs-unstable` | 9.2.4       | `ghc924`              | Yes           |
+| unstable         | `nixpkgs-unstable` | 9.6.6       | `ghc96` or `ghc966`   | Yes           |
+| unstable         | `nixpkgs-unstable` | 9.8.4       | `ghc98` or `ghc984`   | Yes           |
+| unstable         | `nixpkgs-unstable` | 9.10.1      | `ghc910` or `ghc9101` | Yes           |
+| unstable         | `nixpkgs-unstable` | 9.12.1      | `ghc912` or `ghc9121` | Yes           |
 
 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 (in the off chance this