From 17d63282b27555fada48909a471c8b000e1c8f01 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Fri, 14 Apr 2023 15:23:21 -0700
Subject: [PATCH] haskell.compiler: allow overriding source with hadrian

Hadrian (the GHC build tool) is built separately from GHC. This means
that if `haskell.compiler.ghc961` is overridden to add patches, those
patches will _only_ be applied to the GHC portion of the build, and not
the Hadrian build. For example, backporting this patch to GHC 9.6.1
failed because the changes to `hadrian/` files were not reflected in the
Nix build:

https://gitlab.haskell.org/ghc/ghc/-/commit/5ed77deb1b49bff7bae9660487ee4a40a496476d

By lifting `src` and `hadrian` from variables defined in the function
body to parameters with default values, the `hadrian/` files can be
overridden using the `haskell.compiler.ghc961.override` function. For
example:

   self.haskell.compiler.ghc961.override {
     # The GHC 9.6 builder in nixpkgs first builds hadrian with the
     # source tree provided here and then uses the built hadrian to
     # build the rest of GHC. We need to make sure our patches get
     # included in this `src`, then, rather than modifying the tree in
     # the `patchPhase` or `postPatch` of the outer builder.
     src = self.applyPatches {
       src = let
         version = "9.6.1";
       in
         self.fetchurl {
           url = "https://downloads.haskell.org/ghc/${version}/ghc-${version}-src.tar.xz";
           sha256 = "fe5ac909cb8bb087e235de97fa63aff47a8ae650efaa37a2140f4780e21f34cb";
         };

       patches = [
         # Enable response files for linker if supported
         (self.fetchpatch {
           url = "https://gitlab.haskell.org/ghc/ghc/-/commit/5ed77deb1b49bff7bae9660487ee4a40a496476d.patch";
           hash = "sha256-dvenK+EPTZJYXnyfKPdkvLp+zeUmsY9YrWpcGCzYStM=";
         })
       ];
     };
   }

Note that we do have to re-declare the `src` we want, but I'm not sure
of a good way to avoid this while also sharing one set of patches
between the GHC and Hadrian builds.
---
 .../compilers/ghc/common-hadrian.nix          | 30 +++++++++----------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/pkgs/development/compilers/ghc/common-hadrian.nix b/pkgs/development/compilers/ghc/common-hadrian.nix
index 1494b6b9ed40..b90a4934fdba 100644
--- a/pkgs/development/compilers/ghc/common-hadrian.nix
+++ b/pkgs/development/compilers/ghc/common-hadrian.nix
@@ -143,6 +143,20 @@
         return $ verbosity >= Verbose
   ''
 
+, ghcSrc ? (if rev != null then fetchgit else fetchurl) ({
+    inherit url sha256;
+  } // lib.optionalAttrs (rev != null) {
+    inherit rev;
+  })
+
+  # GHC's build system hadrian built from the GHC-to-build's source tree
+  # using our bootstrap GHC.
+, hadrian ? bootPkgs.callPackage ../../tools/haskell/hadrian {
+    ghcSrc = ghcSrc;
+    ghcVersion = version;
+    userSettings = hadrianUserSettings;
+  }
+
 , #  Whether to build sphinx documentation.
   enableDocs ? (
     # Docs disabled for musl and cross because it's a large task to keep
@@ -161,12 +175,6 @@
 assert !enableNativeBignum -> gmp != null;
 
 let
-  src = (if rev != null then fetchgit else fetchurl) ({
-    inherit url sha256;
-  } // lib.optionalAttrs (rev != null) {
-    inherit rev;
-  });
-
   inherit (stdenv) buildPlatform hostPlatform targetPlatform;
 
   inherit (bootPkgs) ghc;
@@ -188,14 +196,6 @@ let
       "*.*.ghc.c.opts += -optc-std=gnu99"
     ];
 
-  # GHC's build system hadrian built from the GHC-to-build's source tree
-  # using our bootstrap GHC.
-  hadrian = bootPkgs.callPackage ../../tools/haskell/hadrian {
-    ghcSrc = src;
-    ghcVersion = version;
-    userSettings = hadrianUserSettings;
-  };
-
   # Splicer will pull out correct variations
   libDeps = platform: lib.optional enableTerminfo ncurses
     ++ lib.optionals (!targetPlatform.isGhcjs) [libffi]
@@ -258,7 +258,7 @@ stdenv.mkDerivation ({
   pname = "${targetPrefix}ghc${variantSuffix}";
   inherit version;
 
-  inherit src;
+  src = ghcSrc;
 
   enableParallelBuilding = true;