patch: automatically adjust width option when terminal is resized

On Fri, 1 Sep 2017, Ralf Goertz wrote:

Am Fri, 1 Sep 2017 07:20:58 -0500 (CDT)
schrieb luke-tierney at uiowa.edu:

On Fri, 1 Sep 2017, Ralf Goertz wrote:

Many good programs like vim adjust their internal width
representation automatically. Why shouldn't R do the same? It seems
quite easy, at least when readline is used:


--- R-3.4.1/src/unix/sys-std.c  2017-03-24 00:03:59.000000000 +0100
+++ R-3.4.1/src/unix/sys-std.patched.c  2017-08-28
09:16:02.714204023 +0200 @@ -1005,6 +1005,9 @@
               // introduced in readline 4.0: only used for >= 6.3
#ifdef HAVE_RL_RESIZE_TERMINAL
               rl_resize_terminal();
+               int rl_height, rl_width;
+               rl_get_screen_size(&rl_height,&rl_width);
+               R_SetOptionWidth(rl_width);
#endif
            }
#endif

The 'width' option affects more than printing to the console; it also
affects, for example, printing to a file via sink() or
capture.output(). So doing this unconditionally would not be a good
idea.  Making it available as an option for those who want it seems
reasonable but still involves a lot more work than these three lines.
It requires designing a protocol for enabling this feature, ideally in
a way that can be made to work well on other interfaces (e.g. Windows,
Mac, RStudio) as well, and it requires documenting all this in a
sensible place. A more complete proposal might well be considered for
adoption.

Hi Luke,

thanks for your explanation. I am not at all familiar with the R source
code nor am I a professional programmer. I found the place to do that
simply by grepping for the signal SIGWINCH. I was, however, aware that
it would need more than those three lines.

As to the other uses of the width option, wouldn't it make sense to have
a separate option for output redirection? Or even have file output
always use the same fixed width, say 80? After all, if the output is
saved to a file this file is probably meant to be viewed in another
context than the R terminal. And even if the width of file output is
affected I don't see any real harm since that is the way it is now. If
one really needs a specific width in such a case s/he can request it by
setting the option manually before outputting to a file.

This could have been designed differently, but it wasn't and making
chnages would cause code to break.

On the other
hand, the documentation says

	 ?width?: controls the maximum number of columns on a line used in
		  ?
		  ?Print.h? and can be changed by re-compiling R.)  Some R
		  consoles automatically change the value when they are 
resized.

Good point.

The Windows R GUI does this if a preference option is set; I don't
know what the default is from just a quick look at the sources.

RStudio does this by default and there is no obvious way, to me at
least, to turn it off, which is unfortunate given the
sink/capture.output issues.

I made changes to R-devel in r73180 to set width if the you set
options(setWidthOnResize = TRUE). By default this option is not set
and the width option is not changed. We'll see if it causes any
problems.

Best,

luke

If *some* consoles already do automatically change the value when
resized why should an instance of R running in a pure terminal emulator
not be allowed to do so? In case there is a good reason, my idea for the
option is as follows. It stays as it is but it can also be negative
indicating that SIGWINCH will lead to an adjustment. That way nothing
changes for those users who do not bother at all. Also, this can easily
be documented, e.g. by appending the following line to the block quoted
above.

		  Others do so when 'width? is negative.

Interfaces which don't or can't use that feature or functions like print
merely have to call "abs(GetOptionWidth())" instead of
"GetOptionWidth()". Luckily, both "int GetOptionWidth()" and "int
attribute_hidden R_SetOptionWidth(int w)" are defined in terms of int,
so it is possible to send and receive negative values. I don't know
about the Windows or Mac interface. But I would imagine that they can
also be made to swallow negative width values rather easily.

Digging a little more I found that there had been the setwidth package
which basically did what I am asking for. Here
<https://groups.google.com/forum/#!topic/vim-r-plugin/SeQCNWxEPwk> the
author of that package (Jakson Aquino) explains that it stopped working
because R started to catch SIGWINCH itself. He continues: ?Perhaps this
feature could be implemented directly in R if someone requested it to
the R Core Team.? There really seems to be a need for this.

Ralf