Subject: 29.1; 29.1: MH-E limited display malfunctions if nothing is matched

From: Chris Siebenmann <[email-masked]>
Date: Tue, 21 Nov 2023 19:28:45 -0500

The summary is that if you use one of the MH-E limit commands, normally
bound under / in MH-E folder mode, and you attempt to limit (narrow) to
something that isn't present, MH-E doesn't handle the situation properly
and winds up with a narrowed list of folder contents displaying nothing
useful instead of reporting that no messages matched.

To reproduce this, you will need NMH and MH-E configured. Then:

* Enter MH-E, for example with 'M-x mh-rmail'.
* widen the display to cover your entire inbox, '/ w'.
* search for something that is not present: 'C-u / s', and change the
  subject to search for to, for example, 'nosuchsubjectstring'.

When you do this, MH-E will first show an error message in a buffer
below the folder window and then narrow the main folder window to a
single line showing 'scan: no messages match specification'. ('/ w' will
then fix the situation.)

When this happens, my *MH-E Log* buffer shows (without the leading
indent):
	Errors when executing: mark +inbox -add -sequence header 0 0
	mark: no messages match specification

The NMH commands MH-E has run (for me) are:
	/usr/bin/mh/pick +inbox 1-382 -list -subject nosuchsubjectstring
	/usr/bin/mh/mark +inbox -add -sequence header 0 0

The output from this pick command if run by hand *without standard
output being a tty* are:
	$ pick +inbox 1-382 -list -subject nosuchsubjectstring | cat
	pick: no messages match specification
	0

The potentially surprising '0' is documented in the current NMH pick
manual page in "Output when no messages are matched". In brief, with
-list and standard output not being a tty, pick deliberately outputs as
'0' to standard output to signal error.

I believe the code problem is in mh-narrow-to-header-field in
mh-limit.el, where it processes pick output using 'string-to-number' on
each line and then pushes the nominal resulting number on to the
msg-list list with:
	(when num (push num msg-list))

I think that there are two problems with this code. The first is that
string-to-number doesn't return nil on non-numbers, it returns 0. The
second is that sometimes a real '0' is present, but should not be pushed
into the message list either. The two together explain why mark was
invoked with the odd '0 0'; one is from the pick error line and one is
from the actual '0' it output.

I am using the version of NMH packaged with Ubuntu 22.04, which is
listed as NMH 1.7.1. My Emacs is a locally compiled 29.1.

NOTE: This reproduces in 'emacs -Q', but this report is submitted from
inside my regular Emacs environment because life is too short. You can
ignore the list of third party packages, load-path shadows, and other
things.

In GNU Emacs 29.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.33,
 cairo version 1.16.0) of 2023-10-30 built on comps3
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Ubuntu 22.04.3 LTS

Configured using:
 'configure --prefix /u/cks/lib/x64-linux/emacs-29.1 --without-gsettings
 --with-x --with-x-toolkit=gtk3 --with-json --with-tree-sitter
 --with-native-compilation=aot'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM HARFBUZZ JPEG JSON LCMS2
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
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  tooltip-mode: t
  global-eldoc-mode: t
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  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
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  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-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:
/u/cks/.emacs.d/elpa/transient-20231121.1154/transient hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/transient
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-core hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-core
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-diminish hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-diminish
/u/cks/.emacs.d/elpa/bind-key-20230203.2004/bind-key hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/bind-key
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-lint hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-lint
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-jump hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-jump
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-delight hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-delight
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-bind-key hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-bind-key
/u/cks/.emacs.d/elpa/use-package-20230426.2324/use-package-ensure hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/use-package/use-package-ensure
/u/cks/.emacs.d/elpa/project-0.10.0/project hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/progmodes/project
/u/cks/.emacs.d/elpa/seq-2.24/seq hides /u/cks/lib/x64-linux/emacs-29.1/share/emacs/29.1/lisp/emacs-lisp/seq

Features:
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Memory information:
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