bug#45518: Ctrl-G Fails to Interrupt Hung Tramp Remote-Compile in Emacs

Using tramp, I had a remote cpp file open in a window.

I pressed "C-c c", which invokes a function in my .emacs called
compile-hereish, which (in this case) invokes the compile command with
the remote directory containing the remote cpp.

Compilation begins as expected.

The cpp file contains a number of syntax errors. There is what I understand to be a longstanding Tramp bug such that, if a lot of outputs (syntax errors) are sent at high speed to the compile window, Tramp hangs.

In emacs 26.2, Ctrl-G (usually ctrl-g three times) would interrupt the hung Tramp window, and indeed cause the errors to be displayed in the window as best as Tramp is able.

In emacs 27.1, Ctrl-G does nothing in this "tramp-hung-while-compiling" situation. I also tried ctrl-c ctrl-c, but that also does nothing. It appears that the only way to kill the hung Tramp compile is to force-quit emacs as a whole at the OS level.

Machine running emacs: MacBook Pro (2015), macos Big Sur v11.1. I am using emacs 27.1 installed via brew-cask on macos.

On the Macbook: ssh -V

OpenSSH_8.1p1, LibreSSL 2.7.3

Remote host for compile: Ubuntu Linux 20.04.1 LTS (GNU/Linux 5.4.0-54-generic x86_64)

On remote host: ssh -V

OpenSSH_8.2p1 Ubuntu-4ubuntu0.1, OpenSSL 1.1.1f 31 Mar 2020

Also on remote host: gcc --version

gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

If I revert back to emacs 26.2 on the Macbook, ctrl-G once again works as expected in the event of a Tramp hang.

I am attaching to the remote host using Tramp-ssh mode, but I also tried Tramp-scp and saw the same behaviour. My .emacs includes:

(setq tramp-default-method "ssh")
(setq tramp-chunksize 500)

The following cpp file (on Ubuntu machine) is sufficient to generate a large number of syntax errors and hang Tramp, blocking ctrl-G (crashing emacs) in emacs 27.1 for me.

// test.cpp

DummyClass(

int validstuff();

int validstuff()

{

return(0);

}

// end test.cpp

Thanks as always.

Following was generated via: M-x report-emacs-bug

In GNU Emacs 27.1 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60 Version 10.14.6 (Build 18G95))
of 2020-08-11 built on builder10-14.porkrind.org
Windowing system distributor 'Apple', version 10.3.2022
System Description: macOS 11.1

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Package cl is deprecated
Mark set

Configured using:
'configure --with-ns '--enable-locallisppath=/Library/Application
Support/Emacs/${version}/site-lisp:/Library/Application
Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES
THREADS JSON PDUMPER

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

Major mode: Fundamental

Minor modes in effect:
global-undo-tree-mode: t
undo-tree-mode: t
global-auto-complete-mode: t
show-paren-mode: t
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tooltip-mode: t
global-eldoc-mode: t
electric-indent-mode: t
mouse-wheel-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
buffer-read-only: t
column-number-mode: t
line-number-mode: t
transient-mark-mode: t

Load-path shadows:
/Users/dgreatwood/.emacs.d/lisp/linum hides /Applications/Emacs.app/Contents/Resources/lisp/linum

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
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epg-config gnus-util rmail rmail-loaddefs text-property-search seq
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Memory information:
((conses 16 70462 8546)
(symbols 48 8556 1)
(strings 32 22334 1877)
(string-bytes 1 713421)
(vectors 16 12259)
(vector-slots 8 156248 17226)
(floats 8 39 36)
(intervals 56 248 0)
(buffers 1000 14))

From:	Duncan Greatwood
Subject:	bug#45518: Ctrl-G Fails to Interrupt Hung Tramp Remote-Compile in Emacs 27.1
Date:	Mon, 28 Dec 2020 17:10:58 -0800