[bug #44714] compatibility mode: .do request and macro expansion via \* collide

[Werner LEMBERG]

URL:
  <http://savannah.gnu.org/bugs/?44714>

                 Summary: compatibility mode: .do request and macro expansion
via \* collide
                 Project: GNU troff
            Submitted by: wl
            Submitted on: Fr 03 Apr 2015 16:03:22 CEST
                Severity: 3 - Normal
              Item Group: None
                  Status: Confirmed
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

Consider the following snippet.


.de1 aa
.  tm compatibility mode = '\\n(.C'
..
.
.cp 1
.
.do tm
\*(aa\


The expected output is


compatibility mode = '0'


since macro `.aa` is defined with `.de1`.  However, due to a bug in troff you
get


compatibility mode = '1'


instead.

Reason of the problem is a clash between the `.do` request and the immediately
following macro expansion via `\*`.

0 In `src/roff/troff/input.cpp`, function `do_request` resets
`compatible_flag` after calling `interpolate_macro` (which handles the
argument of `.do`).
0 `interpolate_macro` calls `token::next` to get the next input token, and
this function expands `\*(aa` and processes tokens until it gets a 'real' one.
 
0 Since `aa` is defined with the `de1` request, it starts internally with a
`PUSH_GROFF_MODE` pseudo-character that makes troff save the compatibility
flag and switch off compatibility mode.  Unfortunately, this happens too
early, and `do_request` overrides this.

An easy work-around is to insert a no-op line.


.do tm
.
\*(aa\


Alas, fixing this bug is not trivial, as far as I can see; it's probably
necessary to redesign the compatibility mode handling.




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