[bug #57616] explicit hyphenation given in tmac/hyphenex.us violated

[Dave]

URL:
  <https://savannah.gnu.org/bugs/?57616>

                 Summary: explicit hyphenation given in tmac/hyphenex.us
violated
                 Project: GNU troff
            Submitted by: barx
            Submitted on: Thu 16 Jan 2020 11:12:12 PM CST
                Category: Core
                Severity: 3 - Normal
              Item Group: Incorrect behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

In US English, my understanding is that a hyphenation expressly provided in
tmac/hyphenex.us overrules whatever other hyphenation points may be generated
by the general patterns in tmac/hyphen.us.  The hyphenex.us entries may be
subject to further restrictions, of course: different .hy values may inhibit
breakpoints that a word in hyphenex.us has.  But groff should never break a
word in hyphenex.us at a point _other_ than the ones it provides.

Meet the word "distraughtly."  hyphenex.us gives it two legal breakpoints:

$ fgrep traugh /usr/share/groff/current/tmac/hyphenex.us
  dis-traught-ly

But with ".hy 4" set, the trick from
http://lists.gnu.org/archive/html/groff/2018-11/msg00023.html to find where
groff hyphenates a word gives:

$ printf ".hy 4\n.ll 1u\n%s\n" distraughtly | nroff 2> /dev/null | sed
'/^$/d'
dis-
traugh-
tly

The latter is clearly not a reasonable breakpoint.

Interestingly, before the fix for bug #53196 was applied, this unwanted
breakpoint did not happen.  I don't yet know whether the fix for that bug
introduced this problem, or something else did.




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