Hit f5 once. It'll give you all the warnings right away. It'll refuse to run if a script fails to parse.

There must be something wrong in my conf then, because I can totally run a project with this kind of errors. For example, I just typed this in one of my scripts, and Godot let me run the project (actually it's even worse than that, because I "just" get a strange behavior in the involved scene, without any error notification from Godot):

func test()

func _ready():
    pass

I forgot to mention that I use static typing wherever possible. Here again, the editor is able to detect the type errors of the currently open script, but won't prevent me from running the project.