[bug #64155] [PATCH] specifying -fZD on command line generates warnings

[G. Branden Robinson]

Follow-up Comment #15, bug #64155 (project groff):

In my working copy of my private branch.  The commit ID will almost certainly
change.


commit f8e966af2985f267ed1efd9c6eeb37e41adca959
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Thu May 25 05:35:25 2023 -0500

    [troff]: Validate a font family before using it.
    
    * src/roff/troff/env.cpp (is_family_valid): New function checks for all
      text styles (R, I, B, BI) and returns true only if the given family
      supports them all.
    
      (family_change): Call `is_family_valid()` on given argument.  If
      invalid, throw diagnostic and ignore `fam` request.
    
    * src/roff/troff/env.h (is_family_valid): Declare; make visible.
    
    * src/roff/troff/input.cpp (main): Call `is_family_valid()` on `-f`
      option argument.  Its invalidity is a fatal error.
    
    Fixes <https://savannah.gnu.org/bugs/?64115>.  Thanks to Dave
    Kemper for the report.
    
    Tested with:
    
    $ echo | ./build/test-groff -fZD -z
    troff: fatal error: 'ZD' is not a valid font family
    $ echo | ./build/test-groff -fH -z
    $ nl ./EXPERIMENTS/validate-family.groff
         1  .tm .fam=\n[.fam]
         2  .fam H
         3  .tm .fam=\n[.fam]
         4  .fam
         5  .tm .fam=\n[.fam]
         6  .fam ZD
         7  .fam BOGUS
         8  .tm .fam=\n[.fam]
         9  .fam
        10  .tm .fam=\n[.fam]
    $ ./build/test-groff ./EXPERIMENTS/validate-family.groff
    .fam=T
    .fam=H
    .fam=T
    troff:./EXPERIMENTS/validate-family.groff:6: error: 'ZD' is not a valid
font family
    troff:./EXPERIMENTS/validate-family.groff:7: error: 'BOGUS' is not a valid
font family
    .fam=T
    .fam=H


I did have to lose the bit of diagnostic about which style was missing,
because the function needed to be callable from two different places and
passing back that information promised to be a pain in the butt.  It would
have meant adding a reference or pointer argument to `is_family_valid`, or
introducing C++ exceptions to groff's exception-free code base.  Or something
similarly grody, I expect.  It didn't seem worth the trouble at this time.


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