ci: add gnu32 cross-compiled 32-bit build

Author: ryanofsky

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        config: [default, llvm]
+        config: [default, llvm, gnu32]
 
     name: build • ${{ matrix.config }}
 

ci/README.md

@@ -18,6 +18,7 @@ To run jobs locally:
 ```bash
 CI_CONFIG=ci/configs/default.sh ci/scripts/run.sh
 CI_CONFIG=ci/configs/llvm.sh    ci/scripts/run.sh
+CI_CONFIG=ci/configs/gnu32.sh   ci/scripts/run.sh
 ```
 
 By default CI jobs will reuse their build directories. `CI_CLEAN=1` can be specified to delete them before running instead.

ci/configs/gnu32.sh

@@ -0,0 +1,9 @@
+CI_DESC="CI job cross-compiling to 32-bit"
+CI_DIR=build-gnu32
+NIX_ARGS=(
+  --arg minimal true
+  --arg crossPkgs 'import <nixpkgs> { crossSystem = { config = "i686-unknown-linux-gnu"; }; }'
+)
+export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter"
+CMAKE_ARGS=(-G Ninja)
+BUILD_ARGS=(-k 0)

shell.nix

@@ -1,24 +1,26 @@
 { pkgs ? import <nixpkgs> {}
+, crossPkgs ? import <nixpkgs> {}
 , enableLibcxx ? false # Whether to use libc++ toolchain and libraries instead of libstdc++
+, minimal ? false # Whether to create minimal shell without extra tools (faster when cross compiling)
 }:
 
 let
   lib  = pkgs.lib;
-  llvm = pkgs.llvmPackages_20;
-  capnproto = pkgs.capnproto.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
+  llvm = crossPkgs.llvmPackages_20;
+  capnproto = crossPkgs.capnproto.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
   clang = if enableLibcxx then llvm.libcxxClang else llvm.clang;
   clang-tools = llvm.clang-tools.override { inherit enableLibcxx; };
-in pkgs.mkShell {
+in crossPkgs.mkShell {
   buildInputs = [
     capnproto
-    llvm.libcxx
   ];
   nativeBuildInputs = with pkgs; [
-    clang
-    clang-tools
     cmake
     include-what-you-use
     ninja
+  ] ++ lib.optionals (!minimal) [
+    clang
+    clang-tools
   ];
 
   # Tell IWYU where its libc++ mapping lives