[bug #55099] [ms]: nesting displays leads to confusing diagnostics

[G. Branden Robinson]

Update of bug #55099 (project groff):

                  Status:               Need Info => Fixed                  
             Assigned to:                    None => gbranden               
             Open/Closed:                    Open => Closed                 
         Planned Release:                    None => 1.23.0                 
                 Summary: undiagnosed error leads to misbehavior => [ms]:
nesting displays leads to confusing diagnostics

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Follow-up Comment #3:

I'm retrospectively regarding this ticket as a complaint about the
uncommunicative error message.  That part of the problem was addressed in a
commit in March.  ms uses diversions extensively, and there were simpler ways
to provoke such a message, such as with a document consisting solely of
".TL".

Here's what the error message looks like now.


s.tmac: error: diversion open while ejecting page (last file seen:
EXPERIMENTS/ds-ds-de.ms) (recovering)


This isn't as good as catching a problem when someone tries to call .DS within
an existing display diversion, but that's precisely the topic of bug #55136 as
Bjarni and Dave noted, so I'll treat that issue orthogonally rather than
regarding either of these two reports as a duplicate.


commit c7b14cb8f84b102dd591843a4e7fc2fbfe2a25a3
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Tue Mar 2 10:38:01 2021 +1100

    tmac/s.tmac: Improve diagnostic messages.
    
    (@diag): New macro wraps .tm request, always prefixing it with the name
    of the macro package, as well as file and line indicators only if these
    are set to non-empty or non-zero values, respectively.
    
    (@error, @warning): Call @diag instead of .tm directly.
    
    (@fatal): Retire; it had only one call site and it would have greatly
    complicated @diag to support calling .ab instead of .tm.  An ugly
    alternative would have been to call .ab with a redundant message after
    calling @diag.
    
    (@divert): New macro wraps .di request, remembering the name of
    the current file (\n[.F]) when a diversion is started.
    
    (@error-recover): Call .ab instead of (deleted) @fatal.
    
    (pg@super-eject): Tell user what the last file name seen was when
    recovering from an unfinished diversion when processing ends.
    
    Examples of improved output compared to groff 1.22.4 follow.
    
    $ (printf ".TL\n" > foo.ms; nroff -ms foo.ms | sed '/^$/d'; rm foo.ms)
    :0: macro error: diversion open while ejecting page (recovering)
    $ (printf ".TL\n" > foo.ms; ./build/test-groff -ms foo.ms \
     | sed '/^$/d'; rm foo.ms)
    s.tmac: error: diversion open while ejecting page (last file seen: foo.ms)
(recovering)
    
    $ (printf '.nr a 23 1\n.while \\n-a .di d\\na\n' > foo.ms; \
      nroff -ms foo.ms | sed '/^$/d'; \rm foo.ms)
    :0: macro error: diversion open while ejecting page (recovering)
    :0: fatal macro error: recovery failed
    $ (printf '.nr a 23 1\n.while \\n-a .di d\\na\n' > foo.ms; \
      ./build/test-groff -ms foo.ms | sed '/^$/d'; \rm foo.ms)
    s.tmac: error: diversion open while ejecting page (last file seen: foo.ms)
(recovering)
    s.tmac: fatal error: recovery failed


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