Add warning when using TaskWithExecutor + InlineLikeExecutor

Summary: This is unsafe and leads to all kinds of bugs. It is unfortunately too late to ban it, but we can at least print a warning to help debugging and maybe discourage new uses.

Reviewed By: yfeldblum

Differential Revision: D29972469

fbshipit-source-id: 1534bcc69eaf8f105998d65c0a6503740924cffa

folly/experimental/coro/Task.h

@@ -23,6 +23,7 @@
 
 #include <folly/CancellationToken.h>
 #include <folly/Executor.h>
+#include <folly/GLog.h>
 #include <folly/Portability.h>
 #include <folly/ScopeGuard.h>
 #include <folly/Traits.h>
@@ -403,6 +404,16 @@ class FOLLY_NODISCARD TaskWithExecutor {
           << "QueuedImmediateExecutor is not safe and is not supported for coro::Task. "
           << "If you need to run a task inline in a unit-test, you should use "
           << "coro::blockingWait instead.";
+      if constexpr (kIsDebug) {
+        if (dynamic_cast<InlineLikeExecutor*>(promise.executor_.get())) {
+          FB_LOG_ONCE(ERROR)
+              << "InlineLikeExecutor is not safe and is not supported for coro::Task. "
+              << "If you need to run a task inline in a unit-test, you should use "
+              << "coro::blockingWait or write your test using the CO_TEST* macros instead."
+              << "If you are using folly::getCPUExecutor, switch to getGlobalCPUExecutor "
+              << "or be sure to call setCPUExecutor first.";
+        }
+      }
 
       auto& calleeFrame = promise.getAsyncFrame();
       calleeFrame.setReturnAddress();