Allow specification of std::functions as native entrypoints from Dart code.

shell/platform/embedder/fixtures/simple_main.dart

@@ -6,3 +6,15 @@ void customEntrypoint() {
 }
 
 void sayHiFromCustomEntrypoint() native "SayHiFromCustomEntrypoint";
+
+
+@pragma('vm:entry-point')
+void customEntrypoint1() {
+  sayHiFromCustomEntrypoint1();
+  sayHiFromCustomEntrypoint2();
+  sayHiFromCustomEntrypoint3();
+}
+
+void sayHiFromCustomEntrypoint1() native "SayHiFromCustomEntrypoint1";
+void sayHiFromCustomEntrypoint2() native "SayHiFromCustomEntrypoint2";
+void sayHiFromCustomEntrypoint3() native "SayHiFromCustomEntrypoint3";

shell/platform/embedder/tests/embedder_context.h

@@ -16,11 +16,23 @@
 #include "flutter/shell/platform/embedder/embedder.h"
 #include "flutter/shell/platform/embedder/tests/embedder_test_resolver.h"
 
+#define CREATE_NATIVE_ENTRY(native_entry)                                   \
+  ({                                                                        \
+    static ::shell::testing::EmbedderContext::NativeEntry closure;          \
+    static Dart_NativeFunction entrypoint = [](Dart_NativeArguments args) { \
+      closure(args);                                                        \
+    };                                                                      \
+    closure = (native_entry);                                               \
+    entrypoint;                                                             \
+  })
+
 namespace shell {
 namespace testing {
 
 class EmbedderContext {
  public:
+  using NativeEntry = std::function<void(Dart_NativeArguments)>;
+
   EmbedderContext(std::string assets_path = "");
 
   ~EmbedderContext();

shell/platform/embedder/tests/embedder_unittests.cc

@@ -59,5 +59,45 @@ TEST_F(EmbedderTest, CanInvokeCustomEntrypoint) {
   ASSERT_TRUE(engine.is_valid());
 }
 
+TEST_F(EmbedderTest, CanInvokeCustomEntrypointMacro) {
+  auto& context = GetEmbedderContext();
+
+  fml::AutoResetWaitableEvent latch1;
+  fml::AutoResetWaitableEvent latch2;
+  fml::AutoResetWaitableEvent latch3;
+
+  // Can be defined separately.
+  auto entry1 = [&latch1](Dart_NativeArguments args) {
+    FML_LOG(ERROR) << "In Callback 1";
+    latch1.Signal();
+  };
+  auto native_entry1 = CREATE_NATIVE_ENTRY(entry1);
+  context.AddNativeCallback("SayHiFromCustomEntrypoint1", native_entry1);
+
+  // Can be wrapped in in the args.
+  auto entry2 = [&latch2](Dart_NativeArguments args) {
+    FML_LOG(ERROR) << "In Callback 2";
+    latch2.Signal();
+  };
+  context.AddNativeCallback("SayHiFromCustomEntrypoint2",
+                            CREATE_NATIVE_ENTRY(entry2));
+
+  // Everything can be inline.
+  context.AddNativeCallback(
+      "SayHiFromCustomEntrypoint3",
+      CREATE_NATIVE_ENTRY([&latch3](Dart_NativeArguments args) {
+        FML_LOG(ERROR) << "In Callback 3";
+        latch3.Signal();
+      }));
+
+  EmbedderConfigBuilder builder(context);
+  builder.SetDartEntrypoint("customEntrypoint1");
+  auto engine = builder.LaunchEngine();
+  latch1.Wait();
+  latch2.Wait();
+  latch3.Wait();
+  ASSERT_TRUE(engine.is_valid());
+}
+
 }  // namespace testing
 }  // namespace shell