Fix arm cross compilation with ghc 8.6.5

nix-tools/regenerate.nix

@@ -55,7 +55,7 @@ in
      ];
     }];
   }).nix-tools.components.exes.plan-to-nix;
-  bootstrap = if pkgs.targetPlatform.isAarch64
+  bootstrap = if pkgs.targetPlatform.isAarch64 && pkgs.buildPlatform.isAarch64
               then haskell-nix.bootstrap.compiler.ghc882
               else haskell-nix.bootstrap.compiler.ghc844;
   in

overlays/bootstrap.nix

@@ -32,26 +32,21 @@ let
     # - What GHC version we should use for bootstrapping.
     # - What Happy version we should use for bootstrapping.
     buildBootstrapper =
-        if final.targetPlatform.isAarch64
+        if final.targetPlatform.isAarch64 && final.buildPlatform.isAarch64
         then {
-            ghc = final.buildPackages.haskell-nix.bootstrap.compiler.ghc882;
+            compilerNixName = "ghc882";
             happyVersion = "1.19.12";
         }
         else {
-            ghc = final.buildPackages.haskell-nix.bootstrap.compiler.ghc844;
+            compilerNixName = "ghc844";
             happyVersion = "1.19.11";
         };
-    # For buildPackages.buildPackages, we just care about the GHC version:
-    buildBuildBootstrapper =
-        if final.targetPlatform.isAarch64
-        then final.buildPackages.buildPackages.haskell-nix.bootstrap.compiler.ghc882
-        else final.buildPackages.buildPackages.haskell-nix.bootstrap.compiler.ghc844;
 in {
   haskell-nix = prev.haskell-nix // {
     # Use this to disable the existing haskell infra structure for testing purposes
     compiler =
         let bootPkgs = with final.buildPackages; {
-                ghc = buildBuildBootstrapper;
+                ghc = final.buildPackages.buildPackages.haskell-nix.bootstrap.compiler."${buildBootstrapper.compilerNixName}";
                 alex = final.haskell-nix.bootstrap.packages.alex-tool {
                   checkMaterialization = false;
                 };
@@ -338,9 +333,9 @@ in {
             '' + installDeps targetPrefix);
         })));
 
-    # Need to use something from 8.8.x as the default on aarch64:
+    # Need to use something from 8.8.x as the default to build aarch64 native compiler:
     defaultCompilerNixName =
-        if final.targetPlatform.isAarch64
+        if final.targetPlatform.isAarch64 && final.buildPlatform.isAarch64
         then "ghc883"
         else "ghc865";
     ghc = final.haskell-nix.compiler."${final.haskell-nix.defaultCompilerNixName}";
@@ -426,7 +421,7 @@ in {
     } // args);
     alex = final.buildPackages.haskell-nix.alex-tool {};
     happy-tool = args: final.haskell-nix.tool "happy" ({
-      version = buildBootstrapper.happyVersion;
+      version = "1.19.12";
       index-state = final.haskell-nix.internalHackageIndexState;
       materialized = ../materialized + "/${
           args.compiler-nix-name or final.haskell-nix.defaultCompilerNixName
@@ -460,7 +455,9 @@ in {
 
 
     # the bootstrap infra structure (pre-compiled ghc; bootstrapped cabal-install, ...)
-    bootstrap = with final.haskell-nix; let ghc = buildBootstrapper.ghc; in {
+    bootstrap = with final.haskell-nix;
+      let ghc = final.buildPackages.haskell-nix.bootstrap.compiler."${buildBootstrapper.compilerNixName}";
+      in {
         # XXX: import ../. will throw away all other overlays, config values, ...
         #      this is not ideal!
         # get binary compilers for bootstrapping.  We'll put the eventual proper
@@ -492,7 +489,7 @@ in {
                 # Only a boot compiler is suitable here
                 ghcOverride = ghc // { isHaskellNixCompiler = ghc.isHaskellNixBootCompiler; };
                 index-state = final.haskell-nix.internalHackageIndexState;
-                materialized = ../materialized/bootstrap/alex;
+                materialized = ../materialized/bootstrap + "/${buildBootstrapper.compilerNixName}/alex";
             } // args);
             alex = bootstrap.packages.alex-tool {};
             happy-tool = args: tool "happy" ({
@@ -501,7 +498,7 @@ in {
                 ghcOverride = ghc // { isHaskellNixCompiler = ghc.isHaskellNixBootCompiler; };
                 inherit (bootstrap.packages) cabal-install nix-tools hpack;
                 index-state = final.haskell-nix.internalHackageIndexState;
-                materialized = ../materialized/bootstrap/happy;
+                materialized = ../materialized/bootstrap + "/${buildBootstrapper.compilerNixName}/happy-${buildBootstrapper.happyVersion}";
             } // args);
             happy = bootstrap.packages.happy-tool {};
             hscolour-tool = args: (hackage-package ({
@@ -510,7 +507,7 @@ in {
                 # Only a boot compiler is suitable here
                 ghcOverride = ghc // { isHaskellNixCompiler = ghc.isHaskellNixBootCompiler; };
                 index-state = final.haskell-nix.internalHackageIndexState;
-                materialized = ../materialized/bootstrap/hscolour;
+                materialized = ../materialized/bootstrap + "/${buildBootstrapper.compilerNixName}/hscolour";
             } // args)).components.exes.HsColour;
             hscolour = bootstrap.packages.hscolour-tool {};
         };

overlays/haskell.nix

@@ -173,7 +173,7 @@ final: prev: {
         snapshots = import ../snapshots.nix { inherit (final) lib ghc-boot-packages; inherit mkPkgSet stackage excludeBootPackages; };
         # Pick a recent LTS snapshot to be our "default" package set.
         haskellPackages =
-            if final.targetPlatform.isAarch64
+            if final.targetPlatform.isAarch64 && final.buildPlatform.isAarch64
             then snapshots."lts-15.13"
             else snapshots."lts-14.13";