* etc/ERC-NEWS: Add entry for option `erc-scrolltobottom-all', and
mention explicit hook-depth intervals reserved by ERC.
* lisp/erc/erc-backend.el (erc--hide-prompt): Change hook depth on
`pre-command-hook' from 91 to 80.
* lisp/erc/erc-goodies.el (erc-input-line-position): Mention secondary
role when new option `erc-scroll-to-bottom-relaxed' is non-nil.
(erc-scrolltobottom-all): New option that decides whether module
`scrolltobottom' affects all windows or just the selected one, as it
always has.
(erc-scrolltobottom-relaxed): New option to leave the prompt
stationary instead of forcing it to the bottom of the window.
(erc-scrolltobottom-mode, erc-scrolltobottom-enable,
erc-scrolltobottom-disable): Use `erc--scrolltobottom-setup' instead
of `erc-add-scroll-to-bottom' for adding and removing local hooks and
instead of ranging over buffers when removing them.  Also add and
remove new hook members when `erc-scrolltobottom-all' is non-nil.
(erc--scrolltobottom-relaxed-commands,
erc--scrolltobottom-window-info,
erc--scrolltobottom-post-force-commands,
erc--scrolltobottom-relaxed-skip-commands): New internal variables.
(erc--scrolltobottom-on-pre-command
erc--scrolltobottom-on-post-command): New functions resembling
`erc-possibly-scroll-to-bottom' that try to avoid scrolling repeatedly
for no reason.
(erc--scrolltobottom-on-pre-command-relaxed,
erc--scrolltobottom-on-post-command-relaxed): New commands to help
implement `erc-scroll-to-bottom-relaxed'.
(erc--scrolltobottom-at-prompt-minibuffer-active): New function to
scroll to bottom on window configuration changes when using the
minibuffer.
(erc--scrolltobottom-all): New function to scroll all windows
displaying the current buffer.
(erc-add-scroll-to-bottom): Deprecate this function because it is now
unused in the default client and trivial to implement otherwise.
(erc--scrolltobottom-setup): New generic function to perform teardown
as well as setup depending on the state of the module's mode variable.
Also add an implementation specifically for `erc-scrolltobottom-all'
that locally modifies different sets of hooks depending on
`erc-scrolltobottom-relaxed'.
(erc--scrolltobottom-on-pre-insert): New generic function that
remembers the last `window-start' and maybe the current screen line
before inserting a message, in order to restore it afterward.
(erc--scrolltobottom-confirm): New function, a replacement for
`erc-scroll-to-bottom' that returns non-nil when it's actually
recentered the window.  For now, used only when
`erc-scrolltobottom-all' is enabled.
(erc-move-to-prompt-setup): Add `erc-move-to-prompt' to
`pre-command-hook' at a depth of 70 in the current buffer.
(erc-keep-place-mode, erc-keep-place-enable): Change hook depth from 0
to 85.
(erc--keep-place-indicator-setup): Add overlay arrow `after-string' in
non-graphical settings in case users have time stamps or other content
occupying the left margin.
(erc-keep-place-indicator-mode, erc-keep-place-indicator-enable):
Change hook depth from 90 to 85 locally so as not to conflict with a
value of t, for append.
(erc--keep-place-indicator-on-global-module): Change hook depth from
90 to 85 locally.
* test/lisp/erc/erc-scenarios-scrolltobottom-relaxed.el: New file.
* test/lisp/erc/erc-scenarios-scrolltobottom.el: New file.
* test/lisp/erc/resources/erc-scenarios-common.el
(erc-scenarios-common--term-size, erc-scenarios-common--run-in-term,
erc-scenarios-common-interactive-debug-term-p,
erc-scenarios-common-with-noninteractive-in-term): New test macro and
supporting helper function and variables to facilitate running
scenario-based tests in an inferior Emacs, in term-mode.
(erc-scenarios-common--at-win-end-p,
erc-scenarios-common--above-win-end-p,
erc-scenarios-common--prompt-past-win-end-p,
erc-scenarios-common--recenter-top-bottom-around,
erc-scenarios-common--recenter-top-bottom,
erc-scenarios-scrolltobottom--normal): New test fixture and assertion
helper functions.
* test/lisp/erc/resources/scrolltobottom/help.eld: New file.
(Bug#64855)