fixes #6186

tests/errmsgs/tgcsafety.nim

@@ -0,0 +1,30 @@
+discard """
+cmd: "nim check $file"
+errormsg: "type mismatch: got <AsyncHttpServer, Port, proc (req: Request): Future[system.void]{.locks: <unknown>.}>"
+nimout: '''
+type mismatch: got <AsyncHttpServer, Port, proc (req: Request): Future[system.void]{.locks: <unknown>.}>
+but expected one of:
+proc serve(server: AsyncHttpServer; port: Port;
+          callback: proc (request: Request): Future[void]; address = ""): Future[void]
+  first type mismatch at position: 3
+  required type: proc (request: Request): Future[system.void]{.closure, gcsafe.}
+  but expression 'cb' is of type: proc (req: Request): Future[system.void]{.locks: <unknown>.}
+  This expression is not GC-safe. Annotate the proc with {.gcsafe.} to get extended error information.
+
+expression: serve(server, Port(7898), cb)
+'''
+"""
+
+# bug #6186
+
+import asyncdispatch, asynchttpserver
+
+var server = newAsyncHttpServer()
+
+var foo = "foo"
+proc cb(req: Request) {.async.} =
+  var baa = foo & "asds"
+  await req.respond(Http200, baa)
+
+asyncCheck server.serve(Port(7898), cb )
+runForever()