[CC:ed the flycheck maintainers; hope you don't mind]

Tim Cross skrev:

>The latest version of rx.el added in commit 2ed71227c626c6cfdc684 seems
>to have broken a number of packages with the error

>Symbol’s function definition is void: rx-submatch-n

>Packages affected include flycheck-color-mode-line, flycheck-joker and
>tide from MELPA.

Thanks for the report. The old rx code was apparently written prior to the double-hyphen convention for marking package-internal symbols, and `rx-submatch-n' is clearly an internal function; I'm not sure why it is used by flycheck.

Of course we could attempt to implement `rx-submatch-n' and what other internal stuff happen to be used by external packages, but that's an open-ended endeavour. Furthermore, it may not always be possible to replicate the expected semantics (internal variables are particularly difficult in that respect).

I'd much rather work with package maintainers to promote the use of stable interfaces. What about the attached patch (untested)?