HACKING

    Copyright 2022-2023 Free Software Foundation, Inc.

    Copying and distribution of this file, with or without
    modification, are permitted in any medium without royalty provided
    the copyright notice and this notice are preserved.

This file contains advice on developing and contributing to groff.  It
assumes that developers will install the 'git' revision control
system and build groff using the instructions in 'INSTALL.repo'.
Familiarize yourself with the structure of the source tree by studying
its 'MANIFEST' file at the top level.

Implementation languages
------------------------

Beyond what is said under "Dependencies" in 'INSTALL.extra',
contributors should note that due to the age of the code base, much of
the C++ dialect employed by groff components, while standard, is older
than C++98--closer to Annotated Reference Manual C++ (Ellis, Stroustrup;
Addison-Wesley, 1990).  groff implements its own string class and the
Standard Template Library is little used.  A modest effort is underway
to update the code to more idiomatic C++98.  Where a C++11 feature
promises to be advantageous, it may be annotated in a code comment.

Portability notes:

* `std::size` is not available in C++98.  Use the `array_length`
  template function in src/include/lib.h instead of `sizeof` and
  dividing.


Automake
--------

A document explaining the basics of GNU Automake and its usage in groff
is available in 'doc/automake.mom'; peruse a PDF rendering in
'doc/automake.pdf' in your build tree.


Testing
-------

Running the test suite with 'make check' after building any substantive
change to groff logic is encouraged.  You should certainly do so, and
confirm that the tests pass, before submitting patches to the groff
mailing list <groff@gnu.org> or Savannah issue tracker.

If you find a defect in a test script, that can be reported via Savannah
like any other bug.


Documenting changes
-------------------

The groff project has a long history and a large, varied audience.
Changes may need to be documented in up to three places depending on
their impact.

1.  Changes should of course be documented in the Git commit message.
    If a change alters only comments or formatting of source code, or
    makes editorial changes to documentation, and does not resolve a
    Savannah ticket, you can stop at that.

2.  The 'ChangeLog' file follows the format and practices documented in
    the GNU Coding Standards.
      https://www.gnu.org/prep/standards/html_node/Change-Logs.html

    The sub-projects in the 'contrib' directory each have their own
    dedicated ChangeLog files.  The file specifications documented there
    are relative to the sub-project, not the root of the groff source
    tree.  When converted to a commit message, add 'contrib/$SUBPROJECT'
    to the entries.

    Apart from 'contrib', groff uses a single (current) 'ChangeLog' file
    for the rest of its source tree.

    It is convenient to write the ChangeLog entry or entries first, then
    construct a commit message from it (or them).

3.  The 'NEWS' file documents changes to groff that a user, not just a
    developer, would notice, not including the resolution of defects.

    As a hypothetical example, correcting a rendering error in tbl(1)
    such that any table with more than 20 rows no longer had the text
    "FOOBAR" spuriously added to some entries would not be a 'NEWS'
    item, because the appearance of such text in the first place is a
    surprising deviation from tbl's ideal and historical behavior.  In
    contrast, adding a command-line option to tbl, or changing the
    meaning of its "expand" region option such that it no longer
    horizontally compresses tables as well, _would_ be 'NEWS'-worthy.


Writing Tests
-------------

Here are some portability notes on writing automated tests.

* Write to the POSIX standard for the shell and utilities where
  possible.  Issue 4 from 1994 is old enough that no contemporary system
  has a good reason for not conforming.  A copy of the standard is
  available at the Open Group's web site.
    https://pubs.opengroup.org/onlinepubs/009656399/toc.pdf

* The GNU coreutils "seq" command is handy but not standardized by
  POSIX.  Replace it with a while loop.

    # emulate "seq 53"
    n=1; while [ $n -le 53 ]; do echo $n; n=$(( n + 1 )); done; unset n

* The "od" command on macOS can put extra space characters (i.e., spaces
  that don't correspond to the input) at the ends of lines when using
  the "od -t c" format; GNU od does not.

  So a regex like this that works with GNU od:
    grep -Eqx '0000000 +A +\\b +B +\\b +C       D +\\n'
  might need to be weakened to the following on macOS.
    grep -Eqx '0000000 +A +\\b +B +\\b +C       D +\\n *'

* The "od" command on macOS does not respect the environment variable
  assignment "LC_ALL=C" when processing byte values 127<x<256 decimal
  and using the "character" output format (option "-t c").  An
  alternative output must be used, like bytewise octal (option "-t o1").
  (macOS od may be non-conforming here, despite the claim of its man
  page.  POSIX Issue 4 od's description says "The type specifier
  character c specifies that bytes will be interpreted as characters
  specified by the current setting of the LC_CTYPE locale category. ...
  Other non-printable characters will be written as one three-digit
  octal number for each byte in the character." (p. 538)  The language
  in Issue 7 (2018) appears unchanged.
    https://pubs.opengroup.org/onlinepubs/9699919799/utilities/od.html )

* macOS sed requires semicolons after commands even if they are followed
  immediately by a closing brace.

  Rewrite
    sed -n '/Foo\./{n;s/^$/FAILURE/;p}'
  as follows.
    sed -n '/Foo\./{n;s/^$/FAILURE/;p;}'

  But see below regarding the opening braces.

* POSIX doesn't say that sed has to accept semicolons as command
  separators after label (':') and test ('t') commands, or after brace
  commands, so macOS sed doesn't.  GNU sed does.

  So rewrite tidy, compact sed scripts like this:
    sed -n '/Foo\./{n;s/^$/FAILURE/;tA;s/.*/SUCCESS/;:A;p}'
  as this more cumbersome alternative.
    sed -n \
      -e '/Foo\./{n;s/^$/FAILURE/;tA;' \
      -e 's/.*/SUCCESS/;:A;' \
      -e 'p;}')

  But see below regarding the opening braces.

  Similarly, a brace sequence like that in this partial sed script:
    /f1/p}}}}}}
  must be rewritten as follows (or with '-e' expressions).
    /f1/p;}
    }
    }
    }
    }
    }

* macOS and GNU sed don't require newlines (or '-e' expression endings)
  after _opening_ braces, but Solaris 11 sed does.

  So the sed script
    /i/{N;/Table of Contents/{N;/Foo[. ][. ]*1/p;};}
  must be rewritten as follows (or with '-e' expressions).
    /i/{
    N;/Table of Contents/{
    N;/Foo[. ][. ]*1/p;
    };
    }


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