Support libffi on Windows (#12200)

Builds the libffi static library on Windows CI and bundles it with the build artifacts.

It uses https://github.com/winlibs/libffi, which is at version 3.3. It is not the most recent version, but that repository seems easiest to integrate into our CI. (Weirdly, the upstream provides an MSVC solution for AArch64 static builds only.) It is assumed #12192 will take care of any potential issues when upgrading to 3.4.x.

.github/workflows/win.yml

@@ -44,6 +44,7 @@ jobs:
             libs/pcre.lib
             libs/iconv.lib
             libs/gc.lib
+            libs/ffi.lib
             libs/z.lib
             libs/mpir.lib
             libs/yaml.lib
@@ -110,6 +111,37 @@ jobs:
           </Project>' > 'Override.props'
 
           MSBuild.exe /p:Platform=x64 /p:Configuration=ReleaseStatic libiconv.vcxproj
+      - name: Download libffi
+        if: steps.cache-libs.outputs.cache-hit != 'true'
+        uses: actions/checkout@v2
+        with:
+          repository: winlibs/libffi
+          ref: libffi-3.3
+          path: libffi
+      - name: Build libffi
+        if: steps.cache-libs.outputs.cache-hit != 'true'
+        working-directory: ./libffi
+        run: |
+          echo '<Project>
+            <PropertyGroup>
+              <ForceImportAfterCppTargets>$(MsbuildThisFileDirectory)\Override.props</ForceImportAfterCppTargets>
+            </PropertyGroup>
+          </Project>' > 'Directory.Build.props'
+
+          echo '<Project>
+            <ItemDefinitionGroup Label="Configuration">
+              <ClCompile>
+                <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+                <DebugInformationFormat>None</DebugInformationFormat>
+                <WholeProgramOptimization>false</WholeProgramOptimization>
+              </ClCompile>
+              <Link>
+                <GenerateDebugInformation>false</GenerateDebugInformation>
+              </Link>
+            </ItemDefinitionGroup>
+          </Project>' > 'Override.props'
+
+          MSBuild.exe /p:PlatformToolset=v143 /p:Platform=x64 /p:Configuration=Release win32\vs16_x64\libffi-msvc.sln -target:libffi:Rebuild
       - name: Download zlib
         if: steps.cache-libs.outputs.cache-hit != 'true'
         run: |
@@ -200,6 +232,7 @@ jobs:
           mv pcre/Release/pcre.lib libs/
           mv libiconv/lib64/libiconvStatic.lib libs/iconv.lib
           mv bdwgc/Release/gc.lib libs/
+          mv libffi/win32/vs16_x64/x64/Release/libffi.lib libs/ffi.lib
           mv zlib/Release/zlibstatic.lib libs/z.lib
           mv mpir/lib/x64/Release/mpir.lib libs/
           mv libyaml/Release/yaml.lib libs/

spec/compiler/ffi/ffi_spec.cr

@@ -1,4 +1,5 @@
-{% skip_file if !flag?(:unix) || flag?(:without_ffi) || flag?(:wasm32) %}
+{% skip_file if flag?(:without_ffi) || flag?(:wasm32) %}
+{% skip_file unless flag?(:unix) || flag?(:win32) %}
 
 require "../spec_helper"
 require "compiler/crystal/ffi"
@@ -167,34 +168,37 @@ describe Crystal::FFI::CallInterface do
       loader.try &.close_all
     end
 
-    it "array" do
-      call_interface = Crystal::FFI::CallInterface.new Crystal::FFI::Type.sint32, [
-        Crystal::FFI::Type.struct([
-          Crystal::FFI::Type.sint32,
-          Crystal::FFI::Type.sint32,
-          Crystal::FFI::Type.sint32,
-          Crystal::FFI::Type.sint32,
-        ]),
-      ] of Crystal::FFI::Type
-
-      loader = Crystal::Loader.new([SPEC_CRYSTAL_LOADER_LIB_PATH])
-      loader.load_library "sum"
-      function_pointer = loader.find_symbol("sum_array")
-
-      return_value = 0_i32
-
-      ary = [1, 2, 3, 4]
-
-      arg_pointers = StaticArray[
-        Pointer.malloc(1, ary.to_unsafe).as(Void*),
-        Pointer(Void).null,
-      ]
-
-      call_interface.call(function_pointer, arg_pointers.to_unsafe, pointerof(return_value).as(Void*))
-      return_value.should eq 10
-    ensure
-      loader.try &.close_all
-    end
+    # passing C array by value is not supported everywhere
+    {% unless flag?(:win32) %}
+      it "array" do
+        call_interface = Crystal::FFI::CallInterface.new Crystal::FFI::Type.sint32, [
+          Crystal::FFI::Type.struct([
+            Crystal::FFI::Type.sint32,
+            Crystal::FFI::Type.sint32,
+            Crystal::FFI::Type.sint32,
+            Crystal::FFI::Type.sint32,
+          ]),
+        ] of Crystal::FFI::Type
+
+        loader = Crystal::Loader.new([SPEC_CRYSTAL_LOADER_LIB_PATH])
+        loader.load_library "sum"
+        function_pointer = loader.find_symbol("sum_array")
+
+        return_value = 0_i32
+
+        ary = [1, 2, 3, 4]
+
+        arg_pointers = StaticArray[
+          Pointer.malloc(1, ary.to_unsafe).as(Void*),
+          Pointer(Void).null,
+        ]
+
+        call_interface.call(function_pointer, arg_pointers.to_unsafe, pointerof(return_value).as(Void*))
+        return_value.should eq 10
+      ensure
+        loader.try &.close_all
+      end
+    {% end %}
   end
 
   describe ".variadic" do