Using incorrect/invalid types for CLI flags raises no warnings to user and is passed through as-is, which can result in unexpected behavior

[peterbe]

Originally posted by @rschristian in #1596 (comment)

Typing preact watch -p XXXX just goes ahead and starts on the default port (8080).
It should error because XXXX is not a number.

[rschristian]

To expound a bit: most args don't have any type validation and rely upon fallbacks or (sometimes) questionable coercion deep into the tool. Warnings aren't raised to the user on such occasions and our assumptions about types can sometimes be faulty (see #1595).

Just wanted to clarify that this isn't just an issue with the port, but many of our arguments. They should all get the same treatment (eventually).