bug#68546: 29.1.90; end-of-file has incorrect data when signaled within a load

[Spencer Baugh <sbaugh@janestreet.com>]

The end-of-file error signaled by read has incorrect data if it's
signaled during a load, by a read unrelated to that load.

1. Create a file "~/read-empty.el" containing:
(read "")
2. (load "~/read-empty.el")
3. Observe the error message:
End of file during parsing: /home/sbaugh/read-empty.el

This error message suggests that there's a syntax error in
read-empty.el, when in fact the syntax error is in something else
entirely.  This is quite confusing.

This happens because end_of_file_error uses load-true-file-name if it's
non-nil, even if the actual read call is unrelated.

One possible fix: a new variable read-file-name could be introduced, and
end_of_file_error could use that instead of load-true-file-name, and
load can just bind read-file-name around read.

As one particular example of the confusing current behavior, a user had
corrupted their ~/.emacs.d/projects so that reading it failed.  Also,
they had a call to (project-forget-zombie-projects) in their init.el.
In combination, this meant Emacs startup errored with:

End of file during parsing: /home/user/.emacs.d/init.el

even though there was no syntax error in init.el at all.

To resolve that, perhaps project--read-project-list could bind
read-file-name to project-list-file, so we'd get an error message which
properly mentions the project file instead.


In GNU Emacs 29.1.90 (build 8, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2024-01-04 built on
 igm-qws-u22796a
Repository revision: 57fa5a53f74e489702825045832f52730c5d550f
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Rocky Linux 8.9 (Green Obsidian)

Configured using:
 'configure 'CFLAGS=-O0 -g3' --with-gif=ifavailable
 --with-x-toolkit=lucid'

Configured features:
CAIRO DBUS FREETYPE GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM
XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
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  file-name-shadow-mode: t
  global-font-lock-mode: t
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  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:
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Memory information:
((conses 16 63231 9564)
 (symbols 48 9475 0)
 (strings 32 22767 1134)
 (string-bytes 1 677438)
 (vectors 16 9316)
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