Better error message and tests for bad await (#19622)

* Better error message and tests for bad await

* Use compiles to check if await is valid

* temp: disable windows noasync test

* Better error report, simplify test

Co-authored-by: flywind <xzsflywind@gmail.com>

lib/pure/asyncmacro.nim

@@ -126,9 +126,19 @@ template await*(f: typed): untyped {.used.} =
     error "await expects Future[T], got " & $typeof(f)
 
 template await*[T](f: Future[T]): auto {.used.} =
-  var internalTmpFuture: FutureBase = f
-  yield internalTmpFuture
-  (cast[typeof(f)](internalTmpFuture)).read()
+  template yieldFuture = yield FutureBase()
+
+  when compiles(yieldFuture):
+    var internalTmpFuture: FutureBase = f
+    yield internalTmpFuture
+    (cast[typeof(f)](internalTmpFuture)).read()
+  else:
+    macro errorAsync(futureError: Future[T]) =
+      error(
+        "Can only 'await' inside a proc marked as 'async'. Use " &
+        "'waitFor' when calling an 'async' proc in a non-async scope instead",
+        futureError)
+    errorAsync(f)
 
 proc asyncSingleProc(prc: NimNode): NimNode =
   ## This macro transforms a single procedure into a closure iterator.