* test/lisp/erc/resources/base/netid/bouncer/barnet-again.eld: Bump
timeouts to 10 seconds.
* test/lisp/erc/resources/base/netid/bouncer/foonet-again.eld: Bump
timeouts to 10 seconds.

* lisp/erc/erc-networks.el
(erc-networks--copy-server-buffer-functions): New internal hook
through which modules can perform housekeeping when server buffers
belonging to the same network context are merged.
(erc-networks--copy-over-server-buffer-contents): Run new internal
hook `erc-networks--copy-server-buffer-functions'.
* lisp/erc/erc-track.el (erc-track-enable, erc-track-disable): Manage
membership in `erc-networks--copy-server-buffer-functions' hook.
(erc-track--replace-killed-buffer): New function to replace server
buffer being killed in `erc-modified-channels-alist'.
* test/lisp/erc/erc-scenarios-base-association.el
(erc-scenarios-networks-merge-server-track): New test.
* test/lisp/erc/resources/networks/merge-server/track.eld: New test
data.  (Bug#60560.)

* test/lisp/erc/erc-services-tests.el
(erc--auth-source-search--plstore-standard,
erc--auth-source-search--plstore-announced,
erc--auth-source-search--plstore-overrides): Kill buffer renamed by
plstore.  In the future, try using the `:buffer' keyword introduced in
Emacs 29.
* test/lisp/erc/resources/erc-d/erc-d-t.el
(erc-d-t-kill-related-buffers): Don't forget about `erc-dcc-chat-mode'
buffers.

* doc/misc/erc.texi: Add linkable note in Modules chapter about some
modules being required.  Also tweak markup in auth-source section.
* etc/ERC-NEWS: Mention the special role of `networks'.
* lisp/erc/erc-backend.el (erc--server-post-connect-hook): Add
internal hook for core modules to perform post-network-process,
pre-protocol config validation even when they haven't been loaded.
(erc--register-connection): Run `erc--server-post-connect-hook'.
* lisp/erc/erc-networks.el (erc-networks--bouncer-targets,
erc-networks-on-MOTD-end): Fix comments and doc strings.  Also change
former from constant to internal variable in case adjustment needed
between releases.
(erc-networks--warn-on-connect): New function to warn about the
`networks' module being absent from `erc-modules'.  This could
probably run at any time up to and including when the logical IRC
connection is established, but doing so at the process/protocol
boundary seems ideal.
* lisp/erc/erc-sasl.el (erc--register-connection): Defer to base
method instead of calling `erc-login' explicitly.
* lisp/erc/erc.el (erc-generate-new-buffer-name): Don't reconcile
buffer names when networks module not in play.
(erc-format-target-and/or-network): Don't assume networks module
loaded.
* test/lisp/erc/erc-scenarios-base-unstable.el:
(erc-scenarios-networks-no-module): New test.
* test/lisp/erc/resources/networks/no-module/basic.eld: New test data
file.  (Bug#60331.)

* lisp/erc/erc-networks.el
(erc-networks-rename-surviving-target-buffer): Don't kill a surviving
target buffer when another, non-target buffer, possibly not even
belonging to ERC, already exists and sports the target's name.
(erc-networks--reconcile-buffer-names): Always append a network-ID
suffix to a target buffer's name if another buffer of that name
already exists.  (Bug#59976.)
* lisp/erc/erc.el (erc, erc-tls): Revise `:id' portion of doc strings.
Thanks to Mike Kazantsev for the suggestion and for filing this bug
and helping solve it.
* test/lisp/erc/erc-networks-tests.el:
(erc-networks-rename-surviving-target-buffer--query-non-target): Add
new test.
* test/lisp/erc/erc-scenarios-base-association-query.el: New file.
* test/lisp/erc/resources/base/assoc/queries/netnick.eld: New file.
* test/lisp/erc/resources/base/assoc/queries/non-erc.eld: New file.

* lisp/erc/erc-sasl.el (erc-sasl--send-cap-ls): Add internal switch
for sending an opening "CAP LS".  The rationale for not enabling this
by default is twofold: one, it more strongly implies that ERC supports
IRCv3 client capability negotiation, which is somewhat disingenuous;
and, two, We'd still be "faking it" by firing and forgetting, and more
balls in the air makes things less predictable.
(erc--register-connection): Possibly send a "CAP LS" before anything
depending on the value of `erc-sasl--send-cap-ls'.  Also, don't
attempt to send `erc-session-username' when it holds an SASL username
because the latter may contain protocol-defying characters.
* test/lisp/erc/resources/base/local-modules/fourth.eld: change user
parameter of "USER" command to reflect nick when `erc-sasl-user' is
set to `:user'.  (Bug#59976.)

* lisp/erc/erc-networks.el (erc-networks--determine): Return the
so-called "given" ID from a non-nil `:id' keyword arg passed to `erc'
or `erc-tls'.
(erc-networks--allow-unknown-network): Add internal variable to
allow IRC session to continue despite the network being unknown.
(erc-networks--set-name): Tell the user about falling back to a given
ID when the network can't be determined.  When that's so, end the
session by destroying the connection unless
`erc-networks--allow-unknown-network' is enabled.  (Bug#59976.)
(erc-networks--ensure-announced): Include the fallback announced
server name in the error message.
* test/lisp/erc/erc-networks-tests.el (erc-networks--set-name): Add
dummy server process and don't expect an error to be signaled.
* test/lisp/erc/erc-scenarios-misc.el
(erc-scenarios-networks-announced-missing): Don't expect an error to
be signaled.
* test/lisp/erc/resources/networks/announced-missing/foonet.eld:
Remove "mode" match pattern.