Build Linux x64 against an isolated sysroot.

.gitea/scripts/install-linux-build-dependencies.sh

@@ -43,11 +43,7 @@ case "$target" in
             "$native_sources"
         sudo apt-get update
 
-        # The full runner image includes these Architecture: all Python tools.
-        # They are unrelated to the build, but make apt replace native Python
-        # while resolving foreign-architecture development packages.
-        sudo env DEBIAN_FRONTEND=noninteractive apt-get remove -y mercurial python3-importlib-metadata python3-jwt
-        install_packages python3 python3-typing-extensions
+        install_packages build-essential cmake gcc-x86-64-linux-gnu g++-x86-64-linux-gnu pkg-config
 
         sudo dpkg --add-architecture amd64
         {
@@ -67,15 +63,22 @@ case "$target" in
                 'Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg'
         } | sudo tee /etc/apt/sources.list.d/ruds-amd64.sources >/dev/null
         sudo apt-get update
-        install_packages \
-            build-essential \
-            cmake \
-            gcc-x86-64-linux-gnu \
-            g++-x86-64-linux-gnu \
+
+        # Foreign development packages contain architecture-specific helper
+        # programs whose maintainer scripts cannot run on the arm64 host.
+        # Download them without installing and extract a link-only sysroot.
+        sysroot=/opt/ruds-x64-sysroot
+        archives=/tmp/ruds-x64-archives
+        sudo mkdir -p "$archives/partial" "$sysroot"
+        sudo env DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+            --download-only \
+            -o Dir::Cache::archives="$archives" \
             libgtk-3-dev:amd64 \
             libwebkit2gtk-4.1-dev:amd64 \
-            libxdo-dev:amd64 \
-            pkg-config
+            libxdo-dev:amd64
+        for package in "$archives"/*.deb; do
+            sudo dpkg-deb --extract "$package" "$sysroot"
+        done
         ;;
     *)
         echo "unsupported Linux build target: $target" >&2

.gitea/workflows/release.yml

@@ -139,9 +139,10 @@ jobs:
       CC_x86_64_unknown_linux_gnu: x86_64-linux-gnu-gcc
       CXX_x86_64_unknown_linux_gnu: x86_64-linux-gnu-g++
       CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER: x86_64-linux-gnu-gcc
-      CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS: -C link-arg=-Wl,-rpath,$ORIGIN -L native=/usr/lib/x86_64-linux-gnu
+      CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS: -C link-arg=-Wl,-rpath,$ORIGIN -L native=/opt/ruds-x64-sysroot/usr/lib/x86_64-linux-gnu -L native=/opt/ruds-x64-sysroot/lib/x86_64-linux-gnu
       PKG_CONFIG_ALLOW_CROSS: "1"
-      PKG_CONFIG_LIBDIR: /usr/lib/x86_64-linux-gnu/pkgconfig:/usr/share/pkgconfig
+      PKG_CONFIG_LIBDIR: /opt/ruds-x64-sysroot/usr/lib/x86_64-linux-gnu/pkgconfig:/opt/ruds-x64-sysroot/usr/lib/pkgconfig:/opt/ruds-x64-sysroot/usr/share/pkgconfig
+      PKG_CONFIG_SYSROOT_DIR: /opt/ruds-x64-sysroot
     steps:
       - name: Check out the tag
         uses: actions/checkout@v4

crates/bds-ui/tests/packaging_assets.rs

@@ -193,38 +193,42 @@ fn tagged_releases_are_built_and_packaged_with_rust_tools() {
         "libwebkit2gtk-4.1-dev:amd64",
         "gcc-x86-64-linux-gnu",
         "Architectures: arm64",
-        "remove -y mercurial python3-importlib-metadata python3-jwt",
-        "install_packages python3 python3-typing-extensions",
+        "--download-only",
+        "dpkg-deb --extract",
+        "/opt/ruds-x64-sysroot",
     ] {
         assert!(
             linux_dependencies.contains(required),
             "Linux dependency setup is missing {required}"
         );
     }
-    let cleanup = linux_dependencies
-        .find("remove -y mercurial python3-importlib-metadata python3-jwt")
-        .expect("runner Python cleanup");
     let multiarch = linux_dependencies
         .find("dpkg --add-architecture amd64")
         .expect("amd64 architecture setup");
     assert!(
-        cleanup < multiarch,
-        "runner-only Python packages must be removed before enabling multiarch"
+        !linux_dependencies.contains("apt-get remove"),
+        "cross-build setup must not replace native runner packages"
     );
-    let native_python = linux_dependencies
-        .find("install_packages python3 python3-typing-extensions")
-        .expect("native Python dependency setup");
     let native_source_filter = linux_dependencies
         .find("'/^Architectures:/d; /^Types: deb$/a Architectures: arm64'")
         .expect("native apt architecture filter");
+    let native_cross_compiler = linux_dependencies
+        .find("install_packages build-essential cmake gcc-x86-64-linux-gnu")
+        .expect("native cross compiler setup");
     assert!(
-        linux_dependencies[native_source_filter..native_python].contains("sudo apt-get update"),
+        linux_dependencies[native_source_filter..native_cross_compiler]
+            .contains("sudo apt-get update"),
         "native apt indexes must be refreshed after constraining the source architecture"
     );
     assert!(
-        native_python < multiarch,
-        "native Python dependencies must be fixed before enabling multiarch"
+        native_cross_compiler < multiarch,
+        "the native cross compiler must be installed before enabling multiarch"
     );
+    assert!(
+        linux_dependencies.find("--download-only").unwrap() > multiarch,
+        "foreign libraries must only be downloaded after enabling multiarch"
+    );
+    assert!(workflow.contains("PKG_CONFIG_SYSROOT_DIR: /opt/ruds-x64-sysroot"));
 
     let workspace_manifest = fs::read_to_string(workspace.join("Cargo.toml")).unwrap();
     let core_manifest = fs::read_to_string(workspace.join("crates/bds-core/Cargo.toml")).unwrap();