Add JavaScriptEventLoopTestSupport module to install executor

Author: kateinoigakukun

Package.swift

@@ -26,5 +26,13 @@ let package = Package(
             dependencies: ["JavaScriptKit", "_CJavaScriptEventLoop"]
         ),
         .target(name: "_CJavaScriptEventLoop"),
+        .target(
+            name: "JavaScriptEventLoopTestSupport",
+            dependencies: [
+                "_CJavaScriptEventLoopTestSupport",
+                .product(name: "JavaScriptEventLoop", package: "JavaScriptKit"),
+            ]
+        ),
+        .target(name: "_CJavaScriptEventLoopTestSupport"),
     ]
 )

Sources/JavaScriptEventLoopTestSupport/JavaScriptEventLoopTestSupport.swift

@@ -0,0 +1,9 @@
+// This module just expose 'JavaScriptEventLoop.installGlobalExecutor' to C ABI
+// See _CJavaScriptEventLoopTestSupport.c for why this is needed
+
+import JavaScriptEventLoop
+
+@_cdecl("swift_javascriptkit_activate_js_executor_impl")
+func swift_javascriptkit_activate_js_executor_impl() {
+    JavaScriptEventLoop.installGlobalExecutor()
+}

Sources/_CJavaScriptEventLoopTestSupport/_CJavaScriptEventLoopTestSupport.c

@@ -0,0 +1,19 @@
+// This 'ctor' function is called at startup time of this program.
+// It's invoked by '_start' of command-line or '_initialize' of reactor.
+// This ctor activate the event loop based global executor automatically
+// before running the test cases. For general applications, applications
+// have to activate the event loop manually on their responsibility.
+// However, XCTest framework doesn't provide a way to run arbitrary code
+// before running all of the test suites. So, we have to do it here.
+//
+// See also: https://github.com/WebAssembly/WASI/blob/main/legacy/application-abi.md#current-unstable-abi
+
+extern void swift_javascriptkit_activate_js_executor_impl(void);
+
+// priority 0~100 is reserved by wasi-libc
+// https://github.com/WebAssembly/wasi-libc/blob/30094b6ed05f19cee102115215863d185f2db4f0/libc-bottom-half/sources/environ.c#L20
+__attribute__((constructor(/* priority */ 200)))
+void swift_javascriptkit_activate_js_executor(void) {
+    swift_javascriptkit_activate_js_executor_impl();
+}
+