Fix cppcoro::make_shared_task() for task<void> case.

Work around bug in MSVC by providing special-case overload of
make_shared_task() for task<void>. Add test for this.

include/cppcoro/shared_task.hpp

@@ -6,6 +6,7 @@
 #define CPPCORO_SHARED_TASK_HPP_INCLUDED
 
 #include <cppcoro/broken_promise.hpp>
+#include <cppcoro/task.hpp>
 
 #include <atomic>
 #include <exception>
@@ -461,6 +462,15 @@ namespace cppcoro
 	{
 		co_return co_await std::move(t);
 	}
+
+#if defined(_MSC_VER) && _MSC_FULL_VER <= 191025019
+	// HACK: Work around bug in MSVC handling of 'co_return <expr>' for void-returning expression.
+	// It doesn't actually evaluate <expr> before calling <promise>.return_void().
+	inline shared_task<void> make_shared_task(task<void> t)
+	{
+		co_await t;
+	}
+#endif
 }
 
 #endif

test/main.cpp

@@ -812,6 +812,36 @@ void testMakeSharedTask()
 	assert(consumerTask1.is_ready());
 }
 
+void testMakeSharedTaskOfVoid()
+{
+	cppcoro::single_consumer_event event;
+
+	auto f = [&]() -> cppcoro::task<>
+	{
+		co_await event;
+	};
+
+	auto t = cppcoro::make_shared_task(f());
+
+	assert(!t.is_ready());
+
+	auto consumer = [](cppcoro::shared_task<> task) -> cppcoro::task<>
+	{
+		co_await task;
+	};
+
+	auto consumerTask0 = consumer(t);
+	auto consumerTask1 = consumer(t);
+
+	assert(!consumerTask0.is_ready());
+	assert(!consumerTask1.is_ready());
+
+	event.set();
+
+	assert(consumerTask0.is_ready());
+	assert(consumerTask1.is_ready());
+}
+
 void testDefaultCancellationTokenIsNotCancellable()
 {
 	cppcoro::cancellation_token t;
@@ -1187,6 +1217,7 @@ int main(int argc, char** argv)
 	testSharedTaskReturningRValueReferenceMovesIntoPromise();
 	testSharedTaskEquality();
 	testMakeSharedTask();
+	testMakeSharedTaskOfVoid();
 
 	testDefaultCancellationTokenIsNotCancellable();
 	testRequestCancellation();