Bug 16603

Summary: Control-C on incremental-search-backward behaves oddly
Product: R Reporter: Frederick Eaton <frederik>
Component: I/OAssignee: R-core <R-core>
Status: ASSIGNED ---    
Severity: enhancement CC: chris, maechler
Priority: P5    
Version: R 3.2.2   
Hardware: Other   
OS: Linux   
Attachments: fix for isearch-sigint bug, applies to R-devel

Description Frederick Eaton 2015-11-18 19:02:45 UTC
I'm running R 3.2.2 (2015-08-14) under Arch Linux.

I've noticed a problem with the command line interface in R for a few years. The problem is that when enter a "backward incremental search" mode by pressing Control-R, and then exit the mode using Control-C, the behavior of R is unexpected and counterintuitive.

First of all, one notices when entering "Ctrl-R some-text Ctrl-C Return" that even though the command line appeared to be empty after Ctrl-C, upon pressing Return it mysteriously fills up with the last command that was encountered by isearch, and then executes that command. This happens no matter how many times I press Ctrl-C. Also, when I do "Ctrl-R some-text Ctrl-C Ctrl-R", it seems that "some-text" is already being searched for.

I haven't looked at the code, but perhaps R needs to somehow clear the input buffer when the user presses Ctrl-C? I think it would be most intuitive if Ctrl-C had the same effect as Ctrl-G in isearch mode. Certainly, it seems undesirable to have an invisible command being executed when the user presses "Return".

Thank you for a (otherwise) great piece of software!
Comment 1 Chris Smowton 2016-01-21 12:01:47 UTC
Came here to mention the same oddity -- either exit i-search and show the prompt on Ctrl-C or do neither. Exiting i-search properly would match bash's behaviour for example, which is the main reason I often try to exit i-search this way then end up accidentally running some recent command or another.
Comment 2 Frederick Eaton 2016-04-30 00:05:36 UTC
However, the question of what exactly Readline or the client
application should do when a SIGINT arrives is somewhat fuzzy, and
there appears to be no Readline function to just cancel the line entry
and clean up state to get the same behavior as Bash (which uses the
basic 'readline()' interface) in Readline callback interface
applications like R or Python. I gather from Chet Ramey that our
SIGINT handler should do something like this:

        rl_free_line_state ();
        rl_cleanup_after_signal ();
        rl_done = 1;
        rl_line_buffer[rl_point = rl_end = rl_mark = 0] = 0;
        rl_callback_handler_remove ();
        /* possibly exit the loop, call rl_callback_handler_install() etc. */

The Python team also calls a new Readline 7 function after


See https://bugs.python.org/file40054/readline-sigcleanup.patch

None of this really makes sense to me, I'd really prefer that
Readline's signal handlers should be installed during our 'select()'
loop, as they were in Readline <= 6.2, and that the Readline SIGINT
handler should take care of noting that the user cancelled a line
entry, as I think is done for the basic "readline()" interface
(haven't checked).

The first issue, which is that Readline 6.3 stopped handling signals
outside of the library itself, also caused us to not be able to resize
terminals running the R CLI:


Things have apparently been broken for several years at least, in both
R and Python. Even applications using Readline 5 seem to show the
isearch-SIGINT bug.

There is a related thread on Stackoverflow:


However, I think the answers there are wrong.
Comment 3 Frederick Eaton 2016-04-30 02:10:11 UTC
me> as I think is done for the basic "readline()" interface (haven't checked).

Actually, I just noticed that the Stackoverflow question is about the
basic "readline()" interface, and the poster is saying that the input
line is not in fact cleared on ^C.
Comment 4 Frederick Eaton 2016-05-02 22:07:51 UTC
Created attachment 2070 [details]
fix for isearch-sigint bug, applies to R-devel

I'm not very familiar with R's source code but I tried to come up with the most reasonable possible workaround for this bug, under the circumstances. Let me know what needs to be changed before it can be accepted. Thanks.
Comment 5 Frederick Eaton 2016-07-07 23:49:27 UTC
I think this is fixed by Martin Maechler in the current R SVN, should I close it? (same with bug 16604)
Comment 6 Martin Maechler 2016-07-09 07:18:24 UTC
The reason it is not closed, is that the fix is only for *some* platforms:
those with a new readline.
E.g., the Mac version of R does not have that.. (for licence reasons) and so the bug is not fixed for R on the mac, AFAIK.