HACKING

GNU Libtool
***********

1. Introduction
===============

This file attempts to describe the processes we use to maintain libtool,
and is not part of a release distribution.

2. Maintenance Notes
====================

* If you incorporate a change from somebody on the net:
  If it is a large change, you must make sure they have signed the
  appropriate paperwork, and be sure to add their name and email
  address to THANKS

* If a change fixes a test, mention the test in the git log entry.

* If somebody reports a new bug, mention his name in the git log entry
  and in the test case you write.

* The correct response to most actual bugs is to write a new test case
  that demonstrates the bug.  Then fix the bug, re-run the test suite,
  and check everything in.

* Some files in the libtool package are not owned by libtool.  These
  files should never be edited here.  These files are:
	COPYING
	INSTALL
	doc/
	    + fdl.texi
	libltdl/
	    + COPYING.LIB
	libltdl/config/
	    + compile
	    + config.guess
	    + config.sub
	    + depcomp
	    + install-sh
	    + mdate-sh
	    + missing
	    + texinfo.tex
  The ones that are important for a release can be updated by ensuring
  gnulib is up-to-date, and running 'bootstrap' to recheck the links are
  correct.

* Changes other than bug fixes must be mentioned in NEWS


3. Test Suite
=============

* When writing tests, make sure the link invocation (first argument to
  AT_CHECK) is on a single line so that 'testsuite -x' displays the
  whole thing.  You can use m4_do or '[... ]dnl' to wrap long lines.

* Use
    make -k check
  liberally, on as many platforms as you can.  Use as many compilers and
  linkers you can.  To run old and new testsuites separately, use
    make check TESTSUITEFLAGS=-V
    make check-local

* The new Autotest testsuite uses keywords to denote test features:
    autoconf		needs Autoconf
    automake		needs Automake
    libltdl		exercises the 'libltdl' library
    libtool		exercises the 'libtool' script
    libtoolize		exercises the 'libtoolize' script
    recursive		runs the suite recursively, with a modified
			'libtool' script and with '-k libtool'
    CXX F77 FC GCJ	exercises a language other than C


4. Naming
=========

* We've adopted the convention that exported Autoconf macros should be
  named with a leading 'LT_' and be documented in the libtool manual.
  Internal macros begin with '_LT_' if they are visible to aclocal, or
  potentially part of an AC_DEFUN/AC_REQUIRE path, or else '_lt_' if
  they are very low level.  This convention was only introduced just
  before libtool-2.0, so there may still be exceptions in the existing
  code.  But all new code should use it.

* All shell variables used internally by libtool's Autoconf macros
  should be named with the a leading 'lt_' (not that they cannot clash
  with the '_lt_' macro namespace).


5. Using git
============

* ChangeLog is generated from git log messages, so you have to format
  the git log carefully.  Use --author for the (first, main) author
  of changesets from others, and sign patches you have reviewed.  If the
  changeset has additional authors that need to be mentioned in the
  generated ChangeLog, then add them to the git log message with:

    Co-authored-by: A U Thor <email@example.com>

  Similarly, if the ChangeLog will need a '(tiny change)' annotation,
  then you should indicate that in the git log message with:

    Copyright-paperwork-exempt: Yes

  Start the git log message with a short one line summary, then an empty
  line, then the rest of the log entry.

  If you forgot to annotate correctly in the git log message, or made
  any other mistake that needs correcting in the distributed ChangeLog
  file, make an amendment against the SHA1 of the errored commit in
  $aux_dir/git-log-fix.

* You may find it useful to install the $aux_dir/git-hooks/commit-msg
  script to .git/hooks in your libtool working directory to help you
  make the best use of git log message metadata.

* Do not ever rewind the public master branch nor any public release
  branch on savannah, neither any release tags once they have been
  published.  Other branches and tags may have different rules.

* Avoid merge commits on the master branch of the public git repository.
  For unpublished changes in your development tree, it's easiest to
  rebase against the current master before applying them, this preserves
  a linear history.


6. Editing '.am' Files
======================

* Always use $(...) and not ${...}

* Use ':', not 'true'.  Use 'exit 1', not 'false'.

* Use '##' comments liberally.  Comment anything even remotely unusual.

* Never use basename or dirname.  Instead use sed.

* Do not use 'cd' within back-quotes, use '$(lt__cd)' instead.
  Otherwise the directory name may be printed, depending on CDPATH.

* In general, if a loop is required, it should be silent.  Then the body
  of the loop itself should print each "important" command it runs.

* Use 4 extra spaces to indent continued dependencies.

* One needs to remember that for our whole logic for the different
  libltdl modes to function correctly, the thing we need to ensure
  *before the client runs libtoolize*, is that the subpackage case is
  correct (because all files may be symlinked there).  All others can
  and will be fixed in the 'libtoolize --ltdl --(non)recursive' stage.


7. Editing '.m4' Files
======================

* Be careful with both 'echo' and '$ECHO'.  As the latter may be one of
   print -r --
   printf %s\n
   func_fallback_echo
  it may not have more than one argument and its value may not be
  eval'ed.  However, the argument may start with a '-' and contain
  backslashes.  As a rule of thumb, use
   echo ..		for literal (constant) strings without leading
			hyphen and no backslashes within,
   $ECHO ".."		otherwise.
   func_echo_all	when multiple arguments are present, or when
			placed in an eval'ed variable.

* The Autoconf manual says that giving an empty parameter is equivalent
  to not giving it at all.  (In particular, the Autoconf manual doesn't
  explain that "FOO()" is calling macro FOO with one empty parameter.)
  To prevent misunderstanding, we should use m4_ifval to check whether
  a parameter is empty, and not $# to check for the number of parameters.

* Any time we add a macro to an older version, lt~obsolete.m4 needs to
  be updated in all newer versions.


8. Abstraction layers in libltdl
=================================

* The libltdl API uses a layered approach to differentiate internal and
  external interfaces, among other things.  To keep the abstraction
  consistent, files in a given layer may only use APIs from files in the
  lower layers.  The ASCII art boxes below represent this stack, from
  top to bottom...

* But first, outside of the stack, there is a convenience header that
  defines the internal interfaces (as evidenced by the 'lt__' prefix to
  the filename!) shared between implementation files in the stack, that
  are however not exported to libltdl clients:

	,-------------.
	|lt__private.h|
	`-------------'

* The top layer of the stack is the libltdl API proper, which includes
  the relevant subsystems automatically.  Clients of libltdl need only
  invoke:

  #include <ltdl.h>

	,------.
	|ltdl.h|
	+------+
	|ltdl.c|
	`------'

* The next layer is comprised of the subsystems of the exported libltdl
  API, which are implemented by files that are named with a leading 'lt_'
  (single underscore!):

	,------------v---------------.
	| lt_error.h | lt_dlloader.h |
	+------------+---------------+
	| lt_error.c | lt_dlloader.c |
	`------------^---------------'

* The next file is used both by the headers that implement it (in which
  case its function is to avoid namespace clashes when linking with the
  GNU C library proper) and is included by code that wants to program
  against a glibc-like interface, in which case it serves to pull in all
  the glibc-like functionality used by libltdl with a simple:

    #include <libltdl/lt__glibc.h>

  It consists of a single file:

	,-----------.
	|lt__glibc.h|
	`-----------'

* Next to last is the libc abstraction layer, which provides a uniform
  API to various system libc interfaces that differ between hosts
  supported by libtool.  Typically, the files that implement this layer
  begin:

    #if defined(LT_CONFIG_H)
    #  include LT_CONFIG_H
    #else
    #  include <config.h>
    #endif
    #include "lt_system.h"

  Or if they are installed headers that must work outside the libtool
  source tree, simply:

    #include <libltdl/lt_system.h>

  This layer's interface is defined by files that are usually named with
  a leading 'lt__':

	,--------------v-------------v------------v--------v---------.
	| lt__dirent.h | lt__alloc.h | lt__strl.h | argz.h | slist.h |
	+--------------+-------------+------------+--------+---------+
	| lt__dirent.c | lt__alloc.c | lt__strl.c | argz.c | slist.c |
	`--------------^-------------^------------^--------^---------'

  (argz.h and slist.h are used independently of libltdl in other projects)

* At the bottom of the stack we have the system abstraction layer,
  which tries to smooth over the cracks where there are differences
  between host systems and compilers.  config.h is generated at
  configure time and is not installed; lt_system.h is an installed
  file and cannot use macros from config.h:

	,-----------.
	|../config.h|
	`-----------'

	,-----------.
	|lt_system.h|
	`-----------'

* Tacked on the side of this stack, attached via the lt_dlloader.h
  definitions are the various implementation modules for run-time module
  loading: preopen.c, dlopen.c etc.


9. Licensing Rules
==================

GNU Libtool uses 3 different licenses for various of the files distributed
herein, with several variations on license text.  It is important that
you use the correct license text in each new file added.  Here are the
texts along with some notes on when each is appropriate.  Appropriate
commenting (shell, C etc) and decoration (m4 etc) assumed throughout.



9.1. Notice preservation

Autoconf macros and files used to generate them need this license, along
with files such as HACKING, NEWS, README, README.alpha, TODO and
ChangeLogs:

   Copyright (C) <year list> Free Software Foundation, Inc.
   Written by <author>, <year>

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 is offered as-is,
without warranty of any kind.



9.2. GPL

Everything else in the distribution has the following license text
unless there is good reason to use one of the other license texts
below:

   Copyright (C) <year list> Free Software Foundation, Inc.
   Written by <author>, <year>

   This file is part of GNU Libtool.

GNU Libtool is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

GNU Libtool is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Libtool; see the file COPYING.  If not, a copy
can be downloaded from  http://www.gnu.org/licenses/gpl.html,
or obtained by writing to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.



9.3. GPL with self extracting version

Some of the sources built atop the options-parser framework use
func_version() to extract their --version output from the copyright
block.  Those files also need the --version copyright text paragraph as
follows:

   <program name> (GNU @PACKAGE@) <version number>
   Written by <author> <email address>.

   This file is part of <parent package name>.

Copyright (C) <year list> Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

<program name> is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

<program name> is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with <program name>; see the file COPYING.  If not, a copy
can be downloaded from http://www.gnu.org/licenses/gpl.html,
or obtained by writing to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.



9.4. GPL with self extracting version and Libtool exception clause

Although the libtool script is generated from 'ltmain.in' according
to the rules in the preceding subsection, it also needs the Libtool
exception clause so that it can be redistributed by other projects
that use libtool:

  <program name> (GNU @PACKAGE@@TIMESTAMP@) <version number>
  Written by <author> <email address>.

  This file is part of GNU Libtool.

Copyright (C) <year list> Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

<program name> is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

As a special exception to the GNU General Public License,
if you distribute this file as part of a program or library that
is built using GNU Libtool, you may include this file under the
same distribution terms that you use for the rest of that program.

<program name> is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with <program name>; see the file COPYING.  If not, a copy
can be downloaded from http://www.gnu.org/licenses/gpl.html,
or obtained by writing to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.



9.5. LGPL with Libtool exception clause

Finally, not only is Libltdl is LGPLed, but it is routinely
redistributed inside projects that use it, so its sources need to use
the following license text citing the LGPL along with Libtool's special
exception clause:

   Copyright (C) <year list> Free Software Foundation, Inc.
   Written by <author>, <year>

   NOTE: The canonical source of this file is maintained with the
   GNU Libtool package.  Report bugs to bug-libtool@gnu.org.

GNU Libltdl is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.

As a special exception to the GNU Lesser General Public License,
if you distribute this file as part of a program or library that
is built using GNU Libtool, you may include this file under the
same distribution terms that you use for the rest of that program.

GNU Libltdl is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with GNU Libltdl; see the file COPYING.LIB.  If not, a
copy can be downloaded from  http://www.gnu.org/licenses/lgpl.html,
or obtained by writing to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

-- 
  Copyright (C) 2004-2008, 2010-2019 Free Software Foundation, Inc.
  Written by Gary V. Vaughan, 2004

  This file is part of GNU Libtool.

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 is offered as-is,
without warranty of any kind.

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