Issue #6601 has been reported by rctay (Tay Ray Chuan).

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Bug #6601: [readline] 
https://bugs.ruby-lang.org/issues/6601

Author: rctay (Tay Ray Chuan)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 1.9.3p236 (2012-06-11) [x86_64-linux]


=begin
= Steps to reproduce
Below are the steps to reproduce from an (({irb})) session. ^ is used to denote the cursor position on the screen.

* Type ((%puts :a%)) then ((%Enter%)). This is to populate the history for reverse-i-search.
 irb(main):001:0> puts :a
 a
 => nil

* Hit ((%Ctrl-R%)) (for reverse-i-search), followed by ((%u%)):
 (reverse-i-search)`u': puts :a
                         ^
* Hit ((%Alt-F%)) (for forward-word).

Observed: reverse-i-search terminated, with an 'f' inserted at cursor position.
 irb(main):002:0> pfuts :a
                    ^

Expected: reverse-i-search terminated, nothing inserted, cursor moves to end of the word (({puts})):
 irb(main):002:0> puts :a
                      ^

Note that other ((%Alt-*%)) commands don't work too (ie ((%x%)) is inserted instead of the command ((%Alt-x%)) being performed), including

* ((%Alt-B%)) (move backward a word)
* ((%Alt-C%)) (capitalize letter)
* ((%Alt-D%)) (delete till end of word)

= Fix

When we hit ((%Alt-F%)) from reverse-i-search, execution arrives at this piece of code in libreadline's (({isearch.c})):

 387       /* ESC still terminates the search, but if there is pending
 388          input or if input arrives within 0.1 seconds (on systems
 389          with select(2)) it is used as a prefix character
 390          with rl_execute_next.  WATCH OUT FOR THIS!  This is intended
 391          to allow the arrow keys to be used like ^F and ^B are used
 392          to terminate the search and execute the movement command.
 393          XXX - since _rl_input_available depends on the application-
 394          settable keyboard timeout value, this could alternatively
 395          use _rl_input_queued(100000) */
 396       if (cxt->lastc == ESC && _rl_input_available ())
 397         rl_execute_next (ESC);

Due to (({readline_getc()})), our (({rl_getc_function()})) implementation, (({IO::getbyte()})) is called, causing all input characters to be "swallowed" into our byte buffer in (({readline_instream})). Thus (({_rl_input_available()})) incorrectly returns false, and the keystrokes (eg. Alt, F) fail to be recognized as a binding for a command.

The proposed fix (attached) uses (({rb_io_read_pending()})) to emulate (({_rl_input_available()})), and calls (({rl_execute_next()})), as libreadline does.

= Affected Versions

Ruby trunk and 1.9.3 (latest) exhibits this issue.

Ruby 1.8 also has exhibits this issue, but the fix would be different since (({rl_getc_function()})) isn't overriden in (({ext/readline/readline.c})).

Tested on readline 6.2; blame'ing the above snippet shows that readline as far back as 5.1 should also give this behaviour.

=end


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