Move more CI to 20.09 (attempt 2)

ci.nix

@@ -24,14 +24,12 @@
     # Update supported-ghc-versions.md to reflect any changes made here.
     {
       ghc865 = true;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2003") {
+    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
       ghc883 = false;
       ghc884 = true;
       ghc8101 = false;
       ghc8102 = true;
       ghc810220201118 = false;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
-      ghc8102 = 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!
@@ -42,9 +40,11 @@
     # We need to use the actual nixpkgs version we're working with here, since the values
     # of 'lib.systems.examples' are not understood between all versions
     let lib = nixpkgs.lib;
-    in lib.optionalAttrs (nixpkgsName == "R2003" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
+    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" "ghc810220201118"])))) {
+  } // lib.optionalAttrs (system == "x86_64-linux" && (
+         (nixpkgsName == "R2009" && __elem compiler-nix-name ["ghc8101" "ghc8102" "ghc810220201118"])
+      || (nixpkgsName == "R2003" && __elem compiler-nix-name ["ghc865"]))) {
     # Windows cross compilation is currently broken on macOS
     inherit (lib.systems.examples) mingwW64;
   } // lib.optionalAttrs (system == "x86_64-linux") {

docs/reference/supported-ghc-versions.md

@@ -1,30 +1,30 @@
 # Supported GHC Versions
 
-The following versions of GHC built on the CI servers and should be included
-in the binary cache (for the default haskell.nix `nixpkgs`).
-
-* 8.6.5 `compiler-nix-name = "ghc865";`
-* 8.8.3 `compiler-nix-name = "ghc883";`
-* 8.8.4 `compiler-nix-name = "ghc884";`
-* 8.10.1 `compiler-nix-name = "ghc8101";`
-* 8.10.2 `compiler-nix-name = "ghc8102";`
-
-Full test suite is run against 8.6.5, 8.8.4 and 8.10.2.
-
-See [ci.nix](https://github.com/input-output-hk/haskell.nix/blob/master/ci.nix)
-for the list of tested GHC versions.
-
-The following GHC versions are not included in CI and will not be cached:
-
-* 8.4.4 `compiler-nix-name = "ghc844";`
-* 8.6.1 `compiler-nix-name = "ghc861";`
-* 8.6.2 `compiler-nix-name = "ghc862";`
-* 8.6.3 `compiler-nix-name = "ghc863";`
-* 8.6.4 `compiler-nix-name = "ghc864";`
-* 8.8.1 `compiler-nix-name = "ghc881";`
-* 8.8.2 `compiler-nix-name = "ghc882";`
-
-See [overlays/bootstrap.nix](https://github.com/input-output-hk/haskell.nix/blob/master/overlays/bootstrap.nix)
-for a list of all the valid `compiler-nix-names`.
+This table shows which versions of GHC are defined, built by CI, and tested. 
+If you use a combination of nixpkgs version and GHC version which is built by our CI, you should get cache hits from our cache.
+
+The "nixpkgs versions" refer to the versions that `haskell.nix` provides; if you use your own version of nixpkgs you will likely not get cache hit
+
+| Nixpkgs version | GHC version   | Defined? | Built? | Tested? |
+| --------------- | ------------- | -------- | ------ | ------- |
+| 20.03           | 8.4.4         | Y        | N      | N       |
+| 20.03           | 8.6.{1,2,3,4} | Y        | N      | N       |
+| 20.03           | 8.6.5         | Y        | Y      | Y       |
+| 20.03           | 8.8.{1,2,3}   | Y        | N      | N       |
+| 20.03           | 8.8.4         | Y        | N      | N       |
+| 20.03           | 8.10.1        | Y        | N      | N       |
+| 20.03           | 8.10.2        | Y        | N      | N       |
+| 20.09           | 8.4.4         | Y        | N      | N       |
+| 20.09           | 8.6.{1,2,3,4} | Y        | N      | N       |
+| 20.09           | 8.6.5         | Y        | Y      | Y       |
+| 20.09           | 8.8.{1,2}     | Y        | N      | N       |
+| 20.09           | 8.8.3         | Y        | Y      | N       |
+| 20.09           | 8.8.4         | Y        | Y      | Y       |
+| 20.09           | 8.10.1        | Y        | Y      | N       |
+| 20.09           | 8.10.2        | Y        | Y      | 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.
+
+See [overlays/bootstrap.nix](https://github.com/input-output-hk/haskell.nix/blob/master/overlays/bootstrap.nix) for a list of all the valid `compiler-nix-names`.
 
 See also: [Instructions on adding new GHC versions](../dev/adding-new-ghc.md).