[ruby-core:101977] [Ruby master Bug#17493] Calling Reline::Unicode.calculate_width appears to lock up when called from emacs or if output is redirected

Issue #17493 has been updated by rsharman (Richard Sharman).

File Patch added

Another way the problem can happen is displaying an EN DASH character, such as in a CSV file produced by LibreOffice.

When a shell is running inside emacs, including the case of running inf-ruby, ANSI sequences are not honoured. In most cases this is harmless; however, in routine cursor_pos it causes problems because it expects to read back characters indicating the cursor position.

A simple fix is to disable this by setting Reline::IOGate to Reline::GeneralIO if the environment variable TERM is set to "dumb", as it in inside emacs; see file Patch.


----------------------------------------
Bug #17493: Calling Reline::Unicode.calculate_width appears to lock up when called from emacs or if output is redirected
https://bugs.ruby-lang.org/issues/17493#change-89829

* Author: rsharman (Richard Sharman)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin17]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
In https://github.com/ruby/reline/pull/224 there is a test program

```
require "reline"

p Reline::Unicode.calculate_width("√")

```
as a test case for bug #17405.  This program hangs when called from an emacs shell.

The problem is that cursor_pos in reline/ansi.rb outputs ESC [ 6 n and expects to be able read in raw mode the cursor position.   This doesn't work when ruby is invoked from a shell inside emacs.

```
--> #1 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/reline/ansi.rb:175:in `cursor_pos'
    #2 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/reline.rb:373:in `may_req_ambiguous_char_width'
    #3 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/reline.rb:359:in `ambiguous_width'
    #4 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/forwardable.rb:238:in `ambiguous_width'
    #5 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/reline/unicode.rb:115:in `get_mbchar_width'
    #6 /Users/richard/.rbenv/versions/3.0/lib/ruby/3.0.0/reline/unicode.rb:143:in `calculate_width'
    #7 /Users/richard/rubystuff/bugs/cursor_pos/test.rb:4
```
Even when run from an actual terminal,  a similar problem occurs if stdout is redirected:

```
$ ruby test2.rb > T

```
The program appears to have locked up at this point; pressing Control-C will not  terminate it.

Is it valid for a routine that calculates a character's width to assume that stdin is actually an ANSI sequence compatible terminal?

(This also occurs with ruby version 2.7.2p137.)


---Files--------------------------------
test.rb (75 Bytes)
Patch (609 Bytes)


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