bug#66628: 30.0.50; EMACS_GENERATE_DYNVARS emits symbols with position

[Basil L. Contovounesios]

Severity: minor
Tags: patch

Given the following two files under /tmp:

  ;;; foo.el -*- lexical-binding: t -*-
  (defvar foo-x)
  (defvar foo-y)
  ;;; foo.el ends here

  ;;; bar.el -*- lexical-binding: t -*-
  (defun bar-x (foo-x) (ignore foo-x))
  (let ((foo-y 1))
    (ignore foo-y)
    (setq foo-y 2))
  ;;; bar.el ends here

  $ EMACS_GENERATE_DYNVARS=1 emacs -Q -batch -f batch-byte-compile foo.el
  Generating /tmp/foo.elc.dynvars

  $ cat foo.elc.dynvars
  (#<symbol foo-y at 62> . "/tmp/foo.el")
  (#<symbol foo-x at 47> . "/tmp/foo.el")

  $ EMACS_DYNVARS_FILE=foo.elc.dynvars emacs -Q -batch -f batch-byte-compile 
bar.el

Since the .dynvars file makes for some bad reading, the last step gives
no diagnostic, though I would expect it to.

Here's a patch that binds print-symbols-bare appropriately:

>From 492ad0f4a97ca43409eb0fefacdfe84b0775cf15 Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <contovob@tcd.ie>
Date: Wed, 18 Oct 2023 15:33:51 +0200
Subject: [PATCH] Print bare symbols for EMACS_GENERATE_DYNVARS

* lisp/emacs-lisp/bytecomp.el (byte-compile--load-dynvars): Remove
redundant goto-char.
(byte-compile-file): Bind print-symbols-bare around .dynvars file
generation.
---
 lisp/emacs-lisp/bytecomp.el | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 92abe6b4624..9d97678379c 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2069,7 +2069,6 @@ byte-compile--load-dynvars
   (and file (not (equal file ""))
        (with-temp-buffer
          (insert-file-contents file)
-         (goto-char (point-min))
          (let ((vars nil)
                var)
            (while (ignore-errors (setq var (read (current-buffer))))
@@ -2284,7 +2283,8 @@ byte-compile-file
         (let ((gen-dynvars (getenv "EMACS_GENERATE_DYNVARS")))
           (when (and gen-dynvars (not (equal gen-dynvars ""))
                      byte-compile--seen-defvars)
-            (let ((dynvar-file (concat target-file ".dynvars")))
+            (let ((dynvar-file (concat target-file ".dynvars"))
+                  (print-symbols-bare t))
               (message "Generating %s" dynvar-file)
               (with-temp-buffer
                 (dolist (var (delete-dups byte-compile--seen-defvars))
-- 
2.42.0

Now I get the following, as expected:

  $ EMACS_GENERATE_DYNVARS=1 emacs -Q -batch -f batch-byte-compile foo.el
  Generating /tmp/foo.elc.dynvars

  $ cat foo.elc.dynvars
  (foo-y . "/tmp/foo.el")
  (foo-x . "/tmp/foo.el")

  $ EMACS_DYNVARS_FILE=foo.elc.dynvars emacs -Q -batch -f batch-byte-compile 
bar.el

  In bar-x:
  bar.el:2:2: Warning: ‘foo-x’ lexically bound in lambda here but declared 
dynamic in: /tmp/foo.el
  bar.el:3:8: Warning: ‘foo-y’ lexically bound in let here but declared dynamic 
in: /tmp/foo.el

WDYT?

Side question: if I replace

  (let ((foo-y 1))
    (ignore foo-y)
    (setq foo-y 2))

with

  (let ((foo-y 1))
    (ignore foo-y)
    (bar-x foo-y))

in bar.el (i.e. foo-y is only read, never set), the .dynvars warning
about foo-y disappears.  I assume this is due to an earlier cconv /
constant propagation pass, is that right?  If so, I'm curious
whether/how the .dynvars feature could be adapted to cope, e.g. by
taking place at an earlier stage.

Thanks,
-- 
Basil

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.18.0, Xaw3d scroll bars) of 2023-10-18 built on tia
Repository revision: 06fc5c24170b820939d3d51071b2957354edcb65
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
System Description: Debian GNU/Linux trixie/sid

Configured using:
 'configure 'CFLAGS=-O2 -ggdb3' -C --prefix=/home/blc/.local
 --enable-checking=structs --with-file-notification=yes
 --with-x-toolkit=lucid --with-x'

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 TREE_SITTER WEBP X11 XAW3D XDBE XIM XINPUT2 XPM
LUCID ZLIB

Important settings:
  value of $LANG: en_IE.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
  minibuffer-regexp-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 puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x 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 rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd touch-screen 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 seq simple cl-generic
indonesian philippine 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
theme-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 x-toolkit
xinput2 x multi-tty move-toolbar make-network-process emacs)

Memory information:
((conses 16 38082 9280) (symbols 48 5209 0) (strings 32 14036 1774)
 (string-bytes 1 387105) (vectors 16 10299)
 (vector-slots 8 156340 16868) (floats 8 23 23) (intervals 56 259 0)
 (buffers 992 10))