Be smarter about switching to TLS from M-x erc

Be smarter about switching to TLS from M-x erc

* lisp/erc/erc.el (erc--warn-unencrypted): Remove unused internal
function.
(erc-select-read-args): Offer to use TLS when user runs M-x erc and
opts for default server and port or provides the well-known IANA TLS
port or enters an ircs:// URL at the server prompt.  For the last two,
do this immediately instead of calling `erc-tls' interactively and
imposing a review of just-chosen values.  Also remove error warnings
and ensure `erc-tls' still works by setting
`erc-server-connect-function' to `erc-open-tls-stream' when
appropriate.  Include the word "URL" in server prompt.
(erc--with-entrypoint-environment): Add new macro for empowering an
entry point's interactive form to bind special variables in their
command's body without shadowing them in the lambda list.
(erc, erc-tls): Add internal keyword argument for interactive use, but
don't make it `keywordp' or advertise its presence.  Also use new
helper macro, `erc--with-entrypoint-environment', to temporarily bind
special vars given by interactive helper `erc-select-read-args'.
* test/lisp/erc/erc-tests.el (erc--with-entrypoint-environment): Add
new test.
(erc-select-read-args): Modify return values to expect additional
internal keyword argument where appropriate.
(erc-tls): Make assertions about environment.
(erc--interactive): New test.  (Bug#60428.)