[bug #57556] Feature request: enforce left and right minimums as required by hyphenation patterns

[Dave]

URL:
  <https://savannah.gnu.org/bugs/?57556>

                 Summary: Feature request: enforce left and right minimums as
required by hyphenation patterns
                 Project: GNU troff
            Submitted by: barx
            Submitted on: Wed 08 Jan 2020 02:13:48 AM CST
                Category: Core
                Severity: 3 - Normal
              Item Group: New feature
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

For most supported languages, groff's hyphenation data assumes a minimum
number of letters that must appear at the beginning or end of a word before or
after a hyphenation point.  The hyphenation algorithm attempting to leave
fewer letters than this minimum will result in erroneous hyphenations.  (The
groff manual's .hy section contains an example of an erroneous division of the
word "splitting" resulting from a .hy value invalid for the English
patterns.)

These required minimums vary depending on the language.  Currently, groff has
a default .hy value that is used regardless of language, and which is invalid
for two of its supported languages (French and English).  By default, groff
should set these minimums based on the selected language.

The hyphenation data historically did not include these minimum values -- even
though they are essential for using the patterns correctly.  Werner Lemberg
points out (http://lists.gnu.org/archive/html/groff/2018-03/msg00002.html)
that since the patterns originate in TeX and not groff, that's the proper
place for this metadata to be introduced.  Later in the thread he adds, "The
TeX hyphenation project is going to [explicitly provide lefthyphenmin and
righthyphenmin values] by introducing YAML headers to all pattern files."  (A
tex-hyphen thread about this can be found at
http://tug.org/pipermail/tex-hyphen/2018-March/001650.html.)

In turn, groff should use these newly supplied values to (1) set .hy to a
valid default for the chosen language, and (2) reject any .hy value
incompatible with the language's hyphenation data.  (The user is free, of
course, to request a value of .hy that specifies greater hyphenation
restrictions than the minimums the language requires.)




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