From 1f167aa460ef03acfe552fcad0410a512ec5fb79 Mon Sep 17 00:00:00 2001
From: Slava Gorbunov <slava@fizlesh.org.ru>
Date: Mon, 27 Oct 2025 20:40:58 +0300
Subject: [PATCH] ghc: provide JavaScript CPP command for ghcjs build

---
 pkgs/development/compilers/ghc/common-hadrian.nix | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pkgs/development/compilers/ghc/common-hadrian.nix b/pkgs/development/compilers/ghc/common-hadrian.nix
index 9de5636d43a3..1097692029db 100644
--- a/pkgs/development/compilers/ghc/common-hadrian.nix
+++ b/pkgs/development/compilers/ghc/common-hadrian.nix
@@ -859,6 +859,12 @@ stdenv.mkDerivation (
       ghc-settings-edit "$settingsFile" \
       "windres command" "${toolPath "windres" installCC}"
     ''
+    + lib.optionalString stdenv.targetPlatform.isGhcjs ''
+      ghc-settings-edit "$settingsFile" \
+        "JavaScript CPP command" "${toolPath "cc" installCC}"
+      ghc-settings-edit "$settingsFile" \
+        "JavaScript CPP flags" "-E"
+    ''
     + ''
 
       # Install the bash completion file.