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.} =
+  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.

tests/async/tasync_noasync.nim

@@ -1,13 +1,42 @@
 discard """
-  errormsg: "'yield' only allowed in an iterator"
+  cmd: "nim check --hints:off --warnings:off $file"
-  cmd: "nim c $file"
+  action: "reject"
-  file: "asyncmacro.nim"
+  nimout: '''
+tasync_noasync.nim(21, 10) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(25, 12) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(28, 10) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(31, 10) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(35, 10) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(38, 10) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+tasync_noasync.nim(40, 8) Error: Can only 'await' inside a proc marked as 'async'. Use 'waitFor' when calling an 'async' proc in a non-async scope instead
+'''
 """
 import async
 
 proc a {.async.} =
   discard
 
+# Bad await usage
+proc nonAsyncProc =
+  await a()
+
+proc nestedNonAsyncProc {.async.} =
+  proc nested =
+    await a()
+
+iterator customIterator: int =
+  await a()
+
+macro awaitInMacro =
+  await a()
+
+type DummyRef = ref object of RootObj
+method awaitInMethod(_: DummyRef) {.base.} =
+  await a()
+
+proc improperMultisync {.multisync.} =
+  await a()
+
 await a()
 
 # if we overload a fallback handler to get