* lisp/erc/erc-backend.el (erc-query-buffer-p): Remove forward declaration.
* lisp/erc/erc.el (erc-query-buffer-p): Defer to `erc-channel-p'.
(erc-channel-p): Refactor and use `erc--fallback-channel-prefixes' for
the default CHANTYPES value.  Honor an empty CHANTYPES value as valid,
e.g., for servers that only support direct messages.
(erc--fallback-channel-prefixes): New variable to hold fallback
CHANTYPES prefixes recommended by RFC1459 and modern authorities on
the matter.
* test/lisp/erc/erc-tests.el (erc-channel-p): Revise test.  (Bug#67220)

* lisp/erc/erc-backend.el (erc-server-parameters)
(erc--isupport-params): Mention parsing and storage behavior regarding
nonstandard "FOO=" tokens.
(erc--parse-isupport-value): Move comment closer to code.
(erc--get-isupport-entry): Treat the empty string as truly null, as
prescribed by the Brocklesby draft cited in the top-level comment.
* test/lisp/erc/erc-tests.el (erc--get-isupport-entry): Add case for
the empty string appearing as a value for an `erc-server-parameters'
item.
(erc-server-005): Assert compat-related behavior of retaining the
empty string as a valid value from a raw "FOO=" token.
(Bug#67220)

* etc/ERC-NEWS: Mention `erc-open' now ignores TGT-LIST.
* lisp/erc/erc.el (erc-open): Set `erc-default-recipients' to a list
containing only the supplied target.  Other values may cause ERC to
malfunction.  Also redo doc string.

* lisp/erc/erc-fill.el (erc-fill-mode): Add reference to
`erc-fill-wrap-mode' in doc string.
(erc--fill-wrap-scrolltobottom-exempt-p): New variable to allow tests
involving `fill-wrap' to opt out of having to enable `scrolltobottom'.
(erc-fill--wrap-ensure-dependencies): Warn and enable
`erc-scrolltobottom-mode' if necessary.
(erc-fill-wrap-mode): Mention workaround for automatically enabling
`scrolltobottom'.
* test/lisp/erc/erc-fill-tests.el (erc-fill-tests--wrap-populate):
Exempt tests from `scrolltobottom' dependency.
* test/lisp/erc/resources/erc-scenarios-common.el: Load `erc-fill'
when compiling.
(erc-scenarios-common--print-trace): Exempt tests using `fill-wrap'
from the `scrolltobottom' dependency by making
`erc--fill-wrap-scrolltobottom-exempt-p' non-nil during test runs.
(Bug#60936)

* lisp/erc/erc.el: Add `custom-loads' library features for group
symbols `erc-spelling' and `erc-imenu' since they aren't defined in
all supported Emacs versions.  Also add groups `erc-sasl' and
`erc-nicks', new libraries recently added to ERC.  Note that this is
unrelated to prefixes generated for the help system.  (Bug#68943)

Avoid eager macro-expansion error in tests files on Emacs 27 and 28 by
ensuring definitions provided by Compat, like `macroexp-file-name',
load first.

* lisp/erc/erc-speedbar.el (erc-speedbar--reset-last-ran-on-timer):
Suppress "`buffer-local-value' is an obsolete generalized variable"
warning on Emacs 29 and below.
* lisp/erc/erc-stamp.el (erc-stamp--time-as-day): Avoid "unused
lexical variable `current-time-list'" warning on 28 and below.
* lisp/erc/erc.el (erc-check-text-conversion): Add `defvar' for
`text-conversion-style' to avoid "reference to free variable" warning
on Emacs 29 and below.
* test/lisp/erc/erc-button-tests.el: Load `erc-button' before `ert-x'.
* test/lisp/erc/erc-fill-tests.el: Load `erc-fill' before `ert-x'.
* test/lisp/erc/erc-goodies-tests.el: Load `erc-goodies' before
`ert-x'.
* test/lisp/erc/erc-networks-tests.el: Explicitly load `erc-compat'
before anything else.
* test/lisp/erc/erc-scenarios-base-renick.el: Update timeouts.
* test/lisp/erc/erc-stamp-tests.el: Load `erc-stamp' before `ert-x'.
* test/lisp/erc/erc-tests.el: Load `erc-ring' before `ert-x'.

* lisp/erc/erc-compat.el: Remove NO-ERROR argument from top-level
`require' for library `compat' because it's guaranteed to be present.
(erc-compat-function, erc-compat-call): Redefine as obsolete aliases
for unprefixed namesakes.
* lisp/erc/erc-fill.el (erc-fill-wrap-nudge): Use `compat-call'
instead of `erc-compat-call'.

* lisp/erc/erc-compat.el (erc-set-write-file-functions):
* lisp/obsolete/iswitchb.el (iswitchb-minibuffer-setup-hook)
(iswitchb-minibuffer-setup):
* lisp/obsolete/longlines.el (longlines-mode):
* lisp/obsolete/rcompile.el (remote-compile):
* lisp/progmodes/cperl-mode.el (cperl-file-style):
* test/lisp/erc/erc-tests.el (erc-ring-previous-command):
Prefer setq-local.