[bug #58162] unicode.tmac re-enables compatibility mode

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?58162>

                 Summary: unicode.tmac re-enables compatibility mode
                 Project: GNU troff
            Submitted by: gbranden
            Submitted on: Sun 12 Apr 2020 03:55:07 AM UTC
                Category: Macro - others
                Severity: 3 - Normal
              Item Group: Incorrect behaviour
                  Status: In Progress
                 Privacy: Public
             Assigned to: gbranden
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

John Gardner noticed the following regression test failure (for a different
software project) on groff git HEAD relative to groff 1.22.4 (which does not
have this bug).


*Command:*
printf '.ds FOO BAR\n\\*[FOO]' | groff -C -Tutf8 | head -n1

*Expected output:*
FOO]

*Actual output:*
BAR


He also identified the cause:


>From a glance, it looks like the `.C` register is being set twice: once by the
calling tty.tmac, and again by unicode.tmac.


So the saved register value was being clobbered.

The real problem here, contrary to my initial thoughts on the mailing list
thread, is not the save/restore approach but a namespace problem.  A common
pattern in macro files and in the man pages in the tree is to just save the .C
register in a register named _C.  This fails as soon as nesting happens.

A while back I ground through all the man pages to make them save to
uniquely-named registers, but out of timidity I did not the stuff in the tmac
directory, where it actually would have done more good.  When I added
save/restore to this file in 2019, I cautiously copied examples from the same
directory.  But they were bad examples in this respect!




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