Subject: bug#54825: 29.0.50; Relax mutual dependency between erc and erc-backend

From: "J.P." <[email-masked]>
Date: Sat, 09 Apr 2022 13:28:29 -0700

Tags: patch

Someone on Libera.Chat recently reported that a recipe similar to the
following results in ERC-occupied portions of the mode-line breaking
down.

  (setq erc-email-userid  "tester/foonet")

  (with-eval-after-load 'erc
    (erc-update-modules)) ; [1]

  (erc
   :server "127.0.0.1"
   :port 6670
   :nick "tester"
   :password "changeme")

Such behavior may be unsurprising to folks familiar with ERC (its root
cause being the interdependency between erc.el and erc-backend.el). But
others may find it unsettling to have a user-facing library only
partially loaded when its namesake feature is provided, not to mention
top-level forms evaluated multiple times. While this situation is
documented in code comments and its possibility warned about in the
Emacs manual, attempting to alleviate some of the attendant awkwardness
seems a worthy endeavor (IMO).

Attached are some traces showing the loading sequence before and after
the proposed changes (which also do away with the surprise produced by
the snippet shown above). As always, superior solutions are welcome.
Thanks.

[1] Please ignore the fact that calling `erc-update-modules' here is
    superfluous. It could just as well be anything that depends on
    library functions provided by ERC.

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.31, cairo version 1.17.4)
 of 2022-04-05 built on localhost
Repository revision: e2fb5ecaea67497224455fdbfe4850a5a74c9d00
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Fedora Linux 35 (Workstation Edition)

Configured using:
 'configure --enable-check-lisp-object-type --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3'
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util text-property-search time-date seq gv
subr-x byte-opt bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer nadvice
simple cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese composite
emoji-zwj charscript charprop case-table epa-hook jka-cmpr-hook help
abbrev obarray oclosure cl-preloaded button loaddefs faces cus-face
macroexp files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 43818 5691)
 (symbols 48 5713 1)
 (strings 32 15808 1645)
 (string-bytes 1 527821)
 (vectors 16 12098)
 (vector-slots 8 168912 12189)
 (floats 8 20 34)
 (intervals 56 221 0)
 (buffers 992 10))
>From 49a929e110f31bdf924d7fa4e2c43cb6a906ff4d Mon Sep 17 00:00:00 2001
From: "F. Jason Park" <[email-masked]>
Date: Mon, 4 Apr 2022 22:38:22 -0700
Subject: [PATCH] Rework mutual dependency between erc and erc-backend

* lisp/erc/erc.el: Declare needed variables exported by erc-backend.el
as special near the top of the file, and only require `erc-backend'
after providing `erc' as a feature at the very end.

* lisp/erc/erc-backend.el: Don't preemptively provide `erc-backend'.

* test/lisp/erc/erc-tests.el (erc--meta--backend-dependencies): Add
utility test to scrape for unused vars that may accumulate over time.
---
 lisp/erc/erc-backend.el    |  1 -
 lisp/erc/erc.el            | 23 ++++++++++++++++++++++-
 test/lisp/erc/erc-tests.el | 21 +++++++++++++++++++++
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
index 398fe6cc9e..5e95156692 100644
--- a/lisp/erc/erc-backend.el
+++ b/lisp/erc/erc-backend.el
@@ -102,7 +102,6 @@
 ;; There's a fairly strong mutual dependency between erc.el and erc-backend.el.
 ;; Luckily, erc.el does not need erc-backend.el for macroexpansion whereas the
 ;; reverse is true:
-(provide 'erc-backend)
 (require 'erc)
 
 ;;;; Variables and options
diff --git a/lisp/erc/erc.el b/lisp/erc/erc.el
index 52fe106f2d..e3ed3c1d96 100644
--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -130,7 +130,26 @@ erc-scripts
   "Running scripts at startup and with /LOAD."
   :group 'erc)
 
-(require 'erc-backend)
+;; Defined in erc-backend
+(defvar erc--server-reconnecting)
+(defvar erc-channel-members-changed-hook)
+(defvar erc-server-367-functions)
+(defvar erc-server-announced-name)
+(defvar erc-server-connect-function)
+(defvar erc-server-connected)
+(defvar erc-server-current-nick)
+(defvar erc-server-filter-data)
+(defvar erc-server-lag)
+(defvar erc-server-last-sent-time)
+(defvar erc-server-parameters)
+(defvar erc-server-process)
+(defvar erc-server-quitting)
+(defvar erc-server-reconnect-count)
+(defvar erc-server-reconnecting)
+(defvar erc-session-client-certificate)
+(defvar erc-session-connector)
+(defvar erc-session-port)
+(defvar erc-session-server)
 
 ;; tunable connection and authentication parameters
 
@@ -7033,6 +7052,8 @@ erc-handle-irc-url
 
 (provide 'erc)
 
+(require 'erc-backend)
+
 ;; Deprecated. We might eventually stop requiring the goodies automatically.
 ;; IMPORTANT: This require must appear _after_ the above (provide 'erc) to
 ;; avoid a recursive require error when byte-compiling the entire package.
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index 520f10dd4e..3c76cb97ca 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -48,6 +48,27 @@ erc--read-time-period
   (cl-letf (((symbol-function 'read-string) (lambda (&rest _) "1d")))
     (should (equal (erc--read-time-period "foo: ") 86400))))
 
+(ert-deftest erc--meta--backend-dependencies ()
+  (with-temp-buffer
+    (insert-file-contents-literally
+     (concat (file-name-sans-extension (symbol-file 'erc)) ".el"))
+    (let ((beg (search-forward ";; Defined in erc-backend"))
+          (end (search-forward "\n\n"))
+          vars)
+      (save-excursion
+        (save-restriction
+          (narrow-to-region beg end)
+          (goto-char (point-min))
+          (with-syntax-table lisp-data-mode-syntax-table
+            (condition-case _
+                (while (push (cadr (read (current-buffer))) vars))
+              (end-of-file)))))
+      (should (= (point) end))
+      (dolist (var vars)
+        (setq var (concat "\\_<" (symbol-name var) "\\_>"))
+        (ert-info (var)
+          (should (save-excursion (search-forward-regexp var nil t))))))))
+
 (ert-deftest erc-with-all-buffers-of-server ()
   (let (proc-exnet
         proc-onet
-- 
2.35.1