From 718851b229754c86bb20507404a50ec07719d057 Mon Sep 17 00:00:00 2001
From: Slava Gorbunov <slava@fizlesh.org.ru>
Date: Fri, 12 Apr 2024 17:50:59 +0300
Subject: [PATCH] haskellPackages.mkDerivation: use emcc as C compiler for
 ghcjs

We need to set up EM_CACHE correctly so that it works, of course.

Note that the solution relies on the assumption that this should only
happen when we cross compile, i.e. the extra logic to account for the
cc-less stdenv in pkgsCross.ghcjs is only present in crossCabalFlags.

Co-authored-by: sternenseemann <sternenseemann@systemli.org>
---
 .../haskell-modules/generic-builder.nix       | 30 ++++++++++++++-----
 pkgs/top-level/release-haskell.nix            | 10 +++++++
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 25480044c9ed..f9acdd0f4a27 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -1,13 +1,24 @@
 { lib, stdenv, buildPackages, buildHaskellPackages, ghc
-, jailbreak-cabal, hscolour, cpphs, nodejs
+, jailbreak-cabal, hscolour, cpphs
 , ghcWithHoogle, ghcWithPackages
+, nodejs
 }:
 
 let
   isCross = stdenv.buildPlatform != stdenv.hostPlatform;
+
+  # Pass the "wrong" C compiler rather than none at all so packages that just
+  # use the C preproccessor still work, see
+  # https://github.com/haskell/cabal/issues/6466 for details.
+  cc =
+    if stdenv.hasCC then "$CC"
+    else if stdenv.hostPlatform.isGhcjs then "${emscripten}/bin/emcc"
+    else "$CC_FOR_BUILD";
+
   inherit (buildPackages)
     fetchurl removeReferencesTo
-    pkg-config coreutils gnugrep glibcLocales;
+    pkg-config coreutils gnugrep glibcLocales
+    emscripten;
 in
 
 { pname
@@ -40,7 +51,8 @@ in
 , enableSharedExecutables ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic && (ghc.enableShared or false)
 , enableDeadCodeElimination ? (!stdenv.isDarwin)  # TODO: use -dead_strip for darwin
-, enableStaticLibraries ? !(stdenv.hostPlatform.isWindows || stdenv.hostPlatform.isWasm)
+# Disabling this for ghcjs prevents this crash: https://gitlab.haskell.org/ghc/ghc/-/issues/23235
+, enableStaticLibraries ? !(stdenv.hostPlatform.isWindows || stdenv.hostPlatform.isWasm || stdenv.hostPlatform.isGhcjs)
 , enableHsc2hsViaAsm ? stdenv.hostPlatform.isWindows
 , extraLibraries ? [], librarySystemDepends ? [], executableSystemDepends ? []
 # On macOS, statically linking against system frameworks is not supported;
@@ -188,10 +200,7 @@ let
   crossCabalFlags = [
     "--with-ghc=${ghcCommand}"
     "--with-ghc-pkg=${ghc.targetPrefix}ghc-pkg"
-    # Pass the "wrong" C compiler rather than none at all so packages that just
-    # use the C preproccessor still work, see
-    # https://github.com/haskell/cabal/issues/6466 for details.
-    "--with-gcc=${if stdenv.hasCC then "$CC" else "$CC_FOR_BUILD"}"
+    "--with-gcc=${cc}"
   ] ++ optionals stdenv.hasCC [
     "--with-ld=${stdenv.cc.bintools.targetPrefix}ld"
     "--with-ar=${stdenv.cc.bintools.targetPrefix}ar"
@@ -315,7 +324,7 @@ let
     optionals doBenchmark benchmarkToolDepends;
   nativeBuildInputs =
     [ ghc removeReferencesTo ] ++ optional (allPkgconfigDepends != []) (assert pkg-config != null; pkg-config) ++
-    setupHaskellDepends ++ collectedToolDepends;
+    setupHaskellDepends ++ collectedToolDepends ++ optional stdenv.hostPlatform.isGhcjs nodejs;
   propagatedBuildInputs = buildDepends ++ libraryHaskellDepends ++ executableHaskellDepends ++ libraryFrameworkDepends;
   otherBuildInputsHaskell =
     optionals doCheck (testDepends ++ testHaskellDepends) ++
@@ -442,6 +451,11 @@ stdenv.mkDerivation ({
   '' + ''
     done
   ''
+  + (optionalString stdenv.hostPlatform.isGhcjs ''
+    export EM_CACHE="$(realpath "$(mktemp -d emcache.XXXXXXXXXX)")"
+    cp -Lr ${emscripten}/share/emscripten/cache/* "$EM_CACHE/"
+    chmod u+rwX -R "$EM_CACHE"
+  '')
   # only use the links hack if we're actually building dylibs. otherwise, the
   # "dynamic-library-dirs" point to nonexistent paths, and the ln command becomes
   # "ln -s $out/lib/links", which tries to recreate the links dir and fails
diff --git a/pkgs/top-level/release-haskell.nix b/pkgs/top-level/release-haskell.nix
index a28c4e8a84ec..5ebc1c78a89f 100644
--- a/pkgs/top-level/release-haskell.nix
+++ b/pkgs/top-level/release-haskell.nix
@@ -473,6 +473,15 @@ let
               inherit (packagePlatforms pkgs.pkgsCross.ghcjs.haskellPackages)
                 ghc
                 hello
+                microlens
+              ;
+            };
+
+            haskell.packages.ghc98 = {
+              inherit (packagePlatforms pkgs.pkgsCross.ghcjs.haskell.packages.ghc98)
+                ghc
+                hello
+                microlens
               ;
             };
 
@@ -480,6 +489,7 @@ let
               inherit (packagePlatforms pkgs.pkgsCross.ghcjs.haskell.packages.ghcHEAD)
                 ghc
                 hello
+                microlens
               ;
             };
           };