can we have test cases for this?

(related old bugs: FS#2017, FS#1795 and FS#384)

Not sure I like the regex. How about this

//(?=.*(?:(?://\s)|(?:(?<!:)//)))

translated.

looking for a terminating pair of slashes where the slashes are followed by white-space or not preceded by a colon. so scheme://domain will not terminate, but both foo:// bar & foo//bar will.

update:

the \s may need to be replaced by a character list to avoid utf8 bytes which can look like spaces under some locale settings (I forget which FS# addressed that, and if it applied to strings inside the parser).

update2
maybe the above regex can be simplified to

//(?=.*(?://\s|[^:]//))

This definitely needs test cases before it's ready to merge