fix cross build

CMakeLists.txt

@@ -1,6 +1,8 @@
 cmake_minimum_required(VERSION 3.16)
 project(TestProject LANGUAGES CXX)
 
+include("${VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake")
+
 find_package(fmt CONFIG REQUIRED)
 find_package(nlohmann_json CONFIG REQUIRED)
 
@@ -15,3 +17,5 @@ target_link_libraries(
   fmt::fmt
   nlohmann_json::nlohmann_json
 )
+
+install(TARGETS test DESTINATION bin)

flake.nix

@@ -15,8 +15,9 @@
       pkgs = import nixpkgs {
         inherit system;
         overlays = [
-          (prev: final: {
+          (final: prev: {
             vcpkg-tool = final.callPackage ./nix/packages/vcpkg-tool/package.nix { };
+            vcpkg = import ./nix/packages/vcpkg/package.nix { inherit (prev) vcpkg; };
           })
         ];
       };
@@ -29,6 +30,14 @@
       test = pkgs.callPackage ./nix/packages/test/package.nix {
         src = ./.;
       };
+
+      test-aarch64 = pkgs.pkgsCross.aarch64-multiplatform.callPackage ./nix/packages/test/package.nix {
+        src = ./.;
+      };
+
+      test-armv7 = pkgs.pkgsCross.armv7l-hf-multiplatform.callPackage ./nix/packages/test/package.nix {
+        src = ./.;
+      };
     });
 
     devShells = forAllSystems (system: pkgs: {

nix/packages/test/package.nix

@@ -14,24 +14,52 @@
 , zip
 }:
 let
+  nixTripletToVcpkgTripletTable = {
+    i686-linux = "x86-linux";
+    x86_64-linux = "x64-linux";
+    armv7l-linux = "arm-linux";
+    aarch64-linux = "arm64-linux";
+  };
+
+  nixTripletToVcpkgArchitectureTable = {
+    i686-linux = "x86";
+    x86_64-linux = "x64";
+    armv7l-linux = "arm";
+    aarch64-linux = "arm64";
+  };
+
+  vcpkgHostTriplet = nixTripletToVcpkgTripletTable.${stdenv.buildPlatform.system}
+                   + lib.optionalString stdenv.buildPlatform.isStatic "-static";
+  vcpkgTargetTriplet = nixTripletToVcpkgTripletTable.${stdenv.hostPlatform.system}
+                   + lib.optionalString stdenv.hostPlatform.isStatic "-static";
+
+  vcpkgHostArch = nixTripletToVcpkgArchitectureTable.${stdenv.buildPlatform.system};
+  vcpkgTargetArch = nixTripletToVcpkgArchitectureTable.${stdenv.hostPlatform.system};
+  
   deps = stdenv.mkDerivation {
     pname = "test-deps";
     version = "0.0.1";
     inherit src;
 
+    # NOTE: for this small example, these hashes seem to match,
+    #       but I have a suspicion that this might not be the case
+    #       for larger projects, where deps depend on their architecture.
     outputHashAlgo = "sha256";
     outputHashMode = "recursive";
     outputHash = {
       "x86_64-linux" = "sha256-nFIbhVp32y+TlFLhuLc0XhlGJZmADgKBo4pd78H3mg8="; 
-      # "x86_64-linux" = ""; 
-      "aarch64-linux" = "";
-      "armv7l-linux" = null;
+      "aarch64-linux" = "sha256-nFIbhVp32y+TlFLhuLc0XhlGJZmADgKBo4pd78H3mg8="; 
+      "armv7l-linux" = "sha256-nFIbhVp32y+TlFLhuLc0XhlGJZmADgKBo4pd78H3mg8=";
     }.${stdenv.hostPlatform.system};
 
     dontConfigure = true;
 
     env = {
       VCPKG_ROOT = "${vcpkg}/share/vcpkg";
+      VCPKG_DEFAULT_TRIPLET = vcpkgTargetTriplet;
+      VCPKG_DEFAULT_HOST_TRIPLET = vcpkgHostTriplet;
+      VCPKG_BINARY_SOURCES = "clear";
+      VCPKG_FORCE_SYSTEM_BINARIES = "1";
     };
 
     nativeBuildInputs = [
@@ -86,36 +114,50 @@ stdenv.mkDerivation {
     cacert
     ninja
     zip
+    pkg-config
   ];
 
   dontConfigure = true;
 
   env = {
     VCPKG_ROOT = "${vcpkg}/share/vcpkg";
+    VCPKG_DEFAULT_TRIPLET = vcpkgTargetTriplet;
+    VCPKG_DEFAULT_HOST_TRIPLET = vcpkgHostTriplet;
+    VCPKG_BINARY_SOURCES = "clear";
+    VCPKG_FORCE_SYSTEM_BINARIES = "1";
   };
 
   buildPhase = let
     vcpkg-install-opts = lib.concatStringsSep " " [
       ''--x-buildtrees-root=$TMP/vcpkg_buildtrees''
       ''--x-packages-root=$TMP/vcpkg_packages''
-      ''--downloads-root=${deps}''
+      ''--downloads-root=$TMP/vcpkg_downloads''
       ''--x-manifest-root=.''
       ''--x-install-root=$TMP/vcpkg_installed''
     ];
 
     cmake-opts = lib.concatStringsSep " " [
       (lib.cmakeFeature "VCPKG_INSTALLED_DIR" "$TMP/vcpkg_installed")
-      (lib.cmakeFeature "VCPKG_TRACE_FIND_PACKAGE" "ON")
+      # (lib.cmakeFeature "VCPKG_TRACE_FIND_PACKAGE" "ON")
       (lib.cmakeFeature "VCPKG_MANIFEST_INSTALL" "OFF")
+
+      (lib.cmakeFeature "VCPKG_TARGET_TRIPLET" vcpkgTargetTriplet)
+      (lib.cmakeFeature "VCPKG_HOST_TRIPLET" vcpkgHostTriplet)
+
+      (lib.cmakeFeature "VCPKG_ROOT" "${vcpkg}/share/vcpkg")
       (lib.cmakeFeature "CMAKE_BUILD_TYPE" "Release")
-      (lib.cmakeFeature "CMAKE_TOOLCHAIN_FILE" "${vcpkg}/share/vcpkg/scripts/buildsystems/vcpkg.cmake")
-      # (lib.cmakeFeature "CMAKE_CXX_COMPILER" "g++")
-      # (lib.cmakeFeature "CMAKE_C_COMPILER" "gcc")
-      # -DVCPKG_INSTALL_OPTIONS="${vcpkg-install-opts}"
+
+      # NOTE: this does not work for cross compilation, because
+      #       you already specify a toolchain. We have to somehow
+      #       inject the library path or an `include` instead?
+      #       source: https://stackoverflow.com/a/64143507
+      # (lib.cmakeFeature "CMAKE_TOOLCHAIN_FILE" "${vcpkg}/share/vcpkg/scripts/buildsystems/vcpkg.cmake")
     ];
   in ''
     runHook preBuild
 
+    cp -r "${deps}/vcpkg_downloads" "$TMP/"
+
     vcpkg install ${vcpkg-install-opts}
 
     cmake ${cmake-opts} -S . -B build -G Ninja

nix/packages/vcpkg/package.nix

@@ -0,0 +1,7 @@
+{ vcpkg }:
+vcpkg.overrideAttrs (prevAttrs: {
+  postPatch = ''
+    sed -i -E -e 's/aarch64-linux-gnu-(as|gcc|g++)/aarch64-unknown-linux-gnu-\1/' scripts/toolchains/linux.cmake
+    sed -i -E -e 's/arm-linux-gnueabihf-(as|gcc|g++)/armv7l-unknown-linux-gnueabihf-\1/' scripts/toolchains/linux.cmake
+  '';
+})