* lisp/subr.el (handler-case): New macro.

* lisp/emacs-lisp/bytecomp.el (bytecomp--displaying-warnings): Use
handler-case.

* test/src/eval-tests.el (eval-tests--handler-bind): Use
handler-case, not condition-case.

* lisp/subr.el (handler-case): Don't use pcase-lambda

Make sure we build the (ERROR-SYMBOL . ERROR-DATA) object only once
when signaling an error, so that its `eq` identity can be used.
It also gets us a tiny bit closer to having real "error objects"
like in most other current programming languages.

* src/eval.c (maybe_call_debugger): Change arglist to receive the error
object instead of receiving the signal and the data separately.
(signal_or_quit): Build the error object right at the beginning so it
stays `eq` to itself.
Rename the `keyboard_quit` arg to `continuable` so say what it does
rather than what it's used for.
(signal_quit_p): Change arg to be the error object rather than just the
error-symbol.

* src/keyboard.c (cmd_error_internal, menu_item_eval_property_1):
Adjust calls to `signal_quit_p` accordingly.

* test/src/eval-tests.el (eval-tests--error-id): New test.

That test relied on `debugger` and `debug-on-signal` in a way that
doesn't work with the new ERT code.

* test/src/emacs-module-tests.el (mod-test-non-local-exit-signal-test):
Use `handler-bind` rather than the debugger.

* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-tests--error-frame, bytecomp--byte-op-error-backtrace):
Make test pass again and simplify, using handler-bind instead
of the previous debugger hack.

Now that `ert.el` uses `handler-bind` instead of `debugger`, some
details of the behavior have changed.  More specifically,
three tests are now broken, but these basically tested the failure
of ERT's machinery to record errors when ERT was run within
a `condition-case`.
AFAICT, these tests do not check for a behavior that we want,
so rather than "fix" them, I disabled them.

* test/lisp/emacs-lisp/ert-tests.el (ert-test-error-debug)
(ert-test-fail-debug-with-condition-case)
(ert-test-should-failure-debugging): Comment out.
(ert-test-with-demoted-errors): It now passes.  Bug#11218 is fixed!

AFAIK, this provides the same semantics as Common Lisp's `handler-bind`,
modulo the differences about how error objects and conditions are
represented.

* lisp/subr.el (handler-bind): New macro.

* src/eval.c (pop_handler): New function.
(Fhandler_Bind_1): New function.
(signal_or_quit): Handle new handlertypes `HANDLER` and `SKIP_CONDITIONS`.
(find_handler_clause): Simplify.
(syms_of_eval): Defsubr `Fhandler_bind_1`.

* doc/lispref/control.texi (Handling Errors): Add `handler-bind`.

* test/src/eval-tests.el (eval-tests--handler-bind): New test.

* lisp/emacs-lisp/lisp-mode.el (lisp-font-lock-keywords):
Move 'handler-bind' from CL-only to generic Lisp.
(handler-bind): Remove indentation setting, it now lives in the macro
definition.

* lisp/emacs-lisp/checkdoc.el (checkdoc-this-string-valid-engine):
Avoid false positive when a variable contains a keybinding (for
example, "C-g").  (Bug#68002)
* test/lisp/emacs-lisp/checkdoc-tests.el
(checkdoc-docstring-avoid-false-positive-ok): New test.

* lisp/erc/erc-button.el (erc-button--display-error-notice-with-keys):
Currently, internal "error notices" do not have timestamps.  However,
this causes alignment issues for non-`fill-wrap' users of left-sided
stamps.  The heuristic used by this change for detecting such stamps
is weak and prone to false negatives.
* lisp/erc/erc-log.el (erc-log-mode, erc-log-enable): Set explicit
depth for `erc--pre-clear-functions' to 50.
(erc-save-buffer-in-logs): Fix partial regression in which redundant
text would appear in logs that have undergone truncation via an
interactive call to this command when the deprecated option
`erc-truncate-on-save' is non-nil.
* lisp/erc/erc-stamp.el (erc-stamp-mode, erc-stamp-enable): Set
depth for `erc--pre-clear-functions' to 40.
(erc-stamp--reset-on-clear): Only add `erc-stamp--insert-date-hook'
when `erc-stamp--date-mode' is active.
* lisp/erc/erc.el (erc-cmd-CLEAR): Rework to honor but improve upon
the old behavior when called from lisp.  Do this by attempting to find
the beginning of the current message and excluding it from the
truncated portion of the buffer.  A NEWS entry describing this
behavior already exists for 5.6.
* test/lisp/erc/erc-scenarios-log.el
(erc-scenarios-log--save-buffer-in-logs/truncate-on-save): New test.
These changes originate from bug#60936.

* lisp/erc/erc-button.el
(erc-button--display-error-notice-with-keys-and-warn): Use
`erc--lwarn' so the warnings buffer is overridable for testing.
* lisp/erc/erc-sasl.el (erc-sasl-mode, erc-sasl-enable): Signal an
`error' instead of calling `erc-error', which continues execution.  In
this special case, the session cannot continue initializing, since
connection registration can't reasonably be expected to complete
successfully.
(erc-sasl--destroy): Don't run `erc-quit-hook', and issue a warning of
level `:error' to get users' attention instead of calling `ding'.
* lisp/erc/erc-speedbar.el
(erc-speedbar--emulate-sidebar-set-window-preserve-size): Don't set
window parameters.  Doing this basically made
`erc-speedbar-toggle-nicknames-window-lock' unusable.
(erc-speedbar--toggle-nicknames-sidebar): Manually unlock the window
after toggling.
(erc-nickbar-mode, erc-nickbar-enable, erc-nickbar-disable): Don't
`ding' when called in a non-ERC buffer, and make sure to call
`erc-speedbar--ensure' from an ERC buffer.  Also, don't disable
minor-mode var when speedbar buffer doesn't exist because that doesn't
ensure it'll be created the next time around, and users may count on
the activation state remaining consistent.
(erc-speedbar-toggle-nicknames-window-lock): Make usable from lisp
with explicit numeric arg.
* lisp/erc/erc-status-sidebar.el (erc-bufbar-mode, erc-bufbar-enable):
Only create the side window from an erc-mode buffer to ensure the
ratio is preserved when burying the current buffer, e.g., with
`custom-buffer-done'.
* lisp/erc/erc.el (erc--warnings-buffer-name, erc--lwarn): New
function, an analog of `lwarn', that allows for overriding the
warnings buffer with the new variable `erc--warnings-buffer-name'.
(erc-cmd-SERVER): Add comment.
* test/lisp/erc/erc-scenarios-sasl.el
(erc-scenarios-sasl--plain-fail): Expect warning instead of error.
* test/lisp/erc/erc-scenarios-status-sidebar.el
(erc-scenarios-status-sidebar--bufbar): Refresh when interactive as
well.
* test/lisp/erc/resources/sasl/plain-failed.eld: Expect EOF instead of
"CAP END".  (Bug#63595)

* lisp/erc/erc-networks.el: Lose some unneeded forward declarations.
* lisp/erc/erc.el (erc-open-socks-tls-stream): Don't conflate SOCKS
with TOR by mentioning a ".onion" address for the `host' parameter.
* test/lisp/erc/erc-tests.el
(erc--check-prompt-input-for-multiline-blanks): Extend timeout.