From fb927d5019d1c5111efcad5008ba10f53481f1d5 Mon Sep 17 00:00:00 2001
From: Ahmad Sattar <thehabbos007@gmail.com>
Date: Thu, 6 Jun 2024 15:30:55 +0200
Subject: [PATCH] BuildRustCrate: proc macros must be built for build's
 platform

When cross compiling proc macros, the proc macro needs to be built for the
build platform's architecture.

Without this change cross compiling from Darwin to Linux would simply
fail because it tries to link to a library with a file extension that
doesn't exist on the builder's platform.
---
 pkgs/build-support/rust/build-rust-crate/default.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pkgs/build-support/rust/build-rust-crate/default.nix b/pkgs/build-support/rust/build-rust-crate/default.nix
index 9ceda041b665..dfe28cc334b5 100644
--- a/pkgs/build-support/rust/build-rust-crate/default.nix
+++ b/pkgs/build-support/rust/build-rust-crate/default.nix
@@ -49,6 +49,8 @@ let
           filename =
             if lib.any (x: x == "lib" || x == "rlib") dep.crateType
             then "${dep.metadata}.rlib"
+            # Adjust lib filename for crates of type proc-macro. Proc macros are compiled/run on the build platform architecture.
+            else if (lib.attrByPath [ "procMacro" ] false dep) then "${dep.metadata}${stdenv.buildPlatform.extensions.library}"
             else "${dep.metadata}${stdenv.hostPlatform.extensions.library}";
         in
         " --extern ${opts}${name}=${dep.lib}/lib/lib${extern}-${filename}"