\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename automake-history.info @settitle automake-history @setchapternewpage on @c %**end of header @copying This manual describes (part of) the history of GNU Automake, a program that creates GNU standards-compliant Makefiles from template files. Copyright @copyright{} 1995--2021 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License.'' @end quotation @end copying @dircategory Software development @direntry * Automake-history: (automake-history). History of Automake development. @end direntry @titlepage @title Brief History of Automake @author David MacKenzie @author Tom Tromey @author Alexandre Duret-Lutz @page @vskip 0pt plus 1filll @insertcopying @end titlepage @contents @ifnottex @node Top @comment node-name, next, previous, up @top Brief History of Automake @insertcopying @menu * Timeline:: The Automake story. * Dependency Tracking Evolution:: Evolution of Automatic Dependency Tracking * Releases:: Release statistics * Copying This Manual:: How to make copies of this manual @detailmenu --- The Detailed Node Listing --- Evolution of Automatic Dependency Tracking * First Take on Dependencies:: Precomputed dependency tracking * Dependencies As Side Effects:: Update at developer compile time * Dependencies for the User:: Update at user compile time * Techniques for Dependencies:: Alternative approaches Techniques for Computing Dependencies * Recommendations for Tool Writers:: * Future Directions for Dependencies:: Copying This Manual * GNU Free Documentation License:: License for copying this manual @end detailmenu @end menu @end ifnottex @node Timeline @chapter Timeline @table @asis @item 1994-09-19 First CVS commit. If we can trust the CVS repository, David J.@tie{}MacKenzie (djm) started working on Automake (or AutoMake, as it was spelt then) this Monday. The first version of the @command{automake} script looks as follows. @example #!/bin/sh status=0 for makefile do if test ! -f $@{makefile@}.am; then echo "automake: $@{makefile@}.am: No such honkin' file" status=1 continue fi exec 4> $@{makefile@}.in done @end example From this you can already see that Automake will be about reading @file{*.am} file and producing @file{*.in} files. You cannot see anything else, but if you also know that David is the one who created Autoconf two years before you can guess the rest. Several commits follow, and by the end of the day Automake is reported to work for GNU fileutils and GNU m4. The modus operandi is the one that is still used today: variable assignments in @file{Makefile.am} files trigger injections of precanned @file{Makefile} fragments into the generated @file{Makefile.in}. The use of @file{Makefile} fragments was inspired by the 4.4BSD @command{make} and include files, however Automake aims to be portable and to conform to the GNU standards for @file{Makefile} variables and targets. At this point, the most recent release of Autoconf is version 1.11, and David is preparing to release Autoconf 2.0 in late October. As a matter of fact, he will barely touch Automake after September. @item 1994-11-05 David MacKenzie's last commit. At this point Automake is a 200 line portable shell script, plus 332 lines of @file{Makefile} fragments. In the @file{README}, David states his ambivalence between ``portable shell'' and ``more appropriate language'': @quotation I wrote it keeping in mind the possibility of it becoming an Autoconf macro, so it would run at configure-time. That would slow configuration down a bit, but allow users to modify the Makefile.am without needing to fetch the AutoMake package. And, the Makefile.in files wouldn't need to be distributed. But all of AutoMake would. So I might reimplement AutoMake in Perl, m4, or some other more appropriate language. @end quotation Automake is described as ``an experimental Makefile generator''. There is no documentation. Adventurous users are referred to the examples and patches needed to use Automake with GNU m4 1.3, fileutils 3.9, time 1.6, and development versions of find and indent. These examples seem to have been lost. However at the time of writing (10 years later in September, 2004) the FSF still distributes a package that uses this version of Automake: check out GNU termutils 2.0. @item 1995-11-12 Tom Tromey's first commit. After one year of inactivity, Tom Tromey takes over the package. Tom was working on GNU cpio back then, and doing this just for fun, having trouble finding a project to contribute to. So while hacking he wanted to bring the @file{Makefile.in} up to GNU standards. This was hard, and one day he saw Automake on @url{ftp://alpha.gnu.org/}, grabbed it and tried it out. Tom didn't talk to djm about it until later, just to make sure he didn't mind if he made a release. He did a bunch of early releases to the Gnits folks. Gnits was (and still is) totally informal, just a few GNU friends who Fran@,cois Pinard knew, who were all interested in making a common infrastructure for GNU projects, and shared a similar outlook on how to do it. So they were able to make some progress. It came along with Autoconf and extensions thereof, and then Automake from David and Tom (who were both gnitsians). One of their ideas was to write a document paralleling the GNU standards, that was more strict in some ways and more detailed. They never finished the GNITS standards, but the ideas mostly made their way into Automake. @item 1995-11-23 Automake 0.20 Besides introducing automatic dependency tracking (@pxref{Dependency Tracking Evolution}), this version also supplies a 9-page manual. At this time @command{aclocal} and @code{AM_INIT_AUTOMAKE} did not exist, so many things had to be done by hand. For instance, here is what a configure.in (this is the former name of the @file{configure.ac} we use today) must contain in order to use Automake 0.20: @example PACKAGE=cpio VERSION=2.3.911 AC_DEFINE_UNQUOTED(PACKAGE, "$PACKAGE") AC_DEFINE_UNQUOTED(VERSION, "$VERSION") AC_SUBST(PACKAGE) AC_SUBST(VERSION) AC_ARG_PROGRAM AC_PROG_INSTALL @end example (Today all of the above is achieved by @code{AC_INIT} and @code{AM_INIT_AUTOMAKE}.) Here is how programs are specified in @file{Makefile.am}: @example PROGRAMS = hello hello_SOURCES = hello.c @end example This looks pretty much like what we do today, except the @code{PROGRAMS} variable has no directory prefix specifying where @file{hello} should be installed: all programs are installed in @samp{$(bindir)}. @code{LIBPROGRAMS} can be used to specify programs that must be built but not installed (it is called @code{noinst_PROGRAMS} nowadays). Programs can be built conditionally using @code{AC_SUBST}itutions: @example PROGRAMS = @@progs@@ AM_PROGRAMS = foo bar baz @end example (@code{AM_PROGRAMS} has since then been renamed to @code{EXTRA_PROGRAMS}.) Similarly scripts, static libraries, and data can be built and installed using the @code{LIBRARIES}, @code{SCRIPTS}, and @code{DATA} variables. However @code{LIBRARIES} were treated a bit specially in that Automake did automatically supply the @file{lib} and @file{.a} prefixes. Therefore to build @file{libcpio.a}, one had to write @example LIBRARIES = cpio cpio_SOURCES = ... @end example Extra files to distribute must be listed in @code{DIST_OTHER} (the ancestor of @code{EXTRA_DIST}). Also extra directories that are to be distributed should appear in @code{DIST_SUBDIRS}, but the manual describes this as a temporary ugly hack (today extra directories should also be listed in @code{EXTRA_DIST}, and @code{DIST_SUBDIRS} is used for another purpose, @pxref{Conditional Subdirectories, , Conditional Subdirectories, automake, GNU Automake}). @item 1995-11-26 Automake 0.21 In less time than it takes to cook a frozen pizza, Tom rewrites Automake using Perl. At this time Perl 5 is only one year old, and Perl 4.036 is in use at many sites. Supporting several Perl versions has been a source of problems through the whole history of Automake. If you never used Perl 4, imagine Perl 5 without objects, without @samp{my} variables (only dynamically scoped @samp{local} variables), without function prototypes, with function calls that needs to be prefixed with @samp{&}, etc. Traces of this old style can still be found in today's @command{automake}. @item 1995-11-28 Automake 0.22 @itemx 1995-11-29 Automake 0.23 Bug fixes. @item 1995-12-08 Automake 0.24 @itemx 1995-12-10 Automake 0.25 Releases are raining. 0.24 introduces the uniform naming scheme we use today, i.e., @code{bin_PROGRAMS} instead of @code{PROGRAMS}, @code{noinst_LIBRARIES} instead of @code{LIBLIBRARIES}, etc. (However @code{EXTRA_PROGRAMS} does not exist yet, @code{AM_PROGRAMS} is still in use; and @code{TEXINFOS} and @code{MANS} still have no directory prefixes.) Adding support for prefixes like that was one of the major ideas in @command{automake}; it has lasted pretty well. AutoMake is renamed to Automake (Tom seems to recall it was Fran@,cois Pinard's doing). 0.25 fixes a Perl 4 portability bug. @item 1995-12-18 Jim Meyering starts using Automake in GNU Textutils. @item 1995-12-31 Fran@,cois Pinard starts using Automake in GNU tar. @item 1996-01-03 Automake 0.26 @itemx 1996-01-03 Automake 0.27 Of the many changes and suggestions sent by Fran@,cois Pinard and included in 0.26, perhaps the most important is the advice that to ease customization a user rule or variable definition should always override an Automake rule or definition. Gordon Matzigkeit and Jim Meyering are two other early contributors that have been sending fixes. 0.27 fixes yet another Perl 4 portability bug. @item 1996-01-13 Automake 0.28 Automake starts scanning @file{configure.in} for @code{LIBOBJS} support. This is an important step because until this version Automake only knew about the @file{Makefile.am}s it processed. @file{configure.in} was Autoconf's world and the link between Autoconf and Automake had to be done by the @file{Makefile.am} author. For instance, if @file{config.h} was generated by @file{configure}, it was the package maintainer's responsibility to define the @code{CONFIG_HEADER} variable in each @file{Makefile.am}. Succeeding releases will rely more and more on scanning @file{configure.in} to better automate the Autoconf integration. 0.28 also introduces the @code{AUTOMAKE_OPTIONS} variable and the @option{--gnu} and @option{--gnits} options, the latter being stricter. @item 1996-02-07 Automake 0.29 Thanks to @file{configure.in} scanning, @code{CONFIG_HEADER} is gone, and rebuild rules for @file{configure}-generated file are automatically output. @code{TEXINFOS} and @code{MANS} converted to the uniform naming scheme. @item 1996-02-24 Automake 0.30 The test suite is born. It contains 9 tests. From now on test cases will be added pretty regularly (@pxref{Releases}), and this proved to be really helpful later on. @code{EXTRA_PROGRAMS} finally replaces @code{AM_PROGRAMS}. All the third-party Autoconf macros, written mostly by Fran@,cois Pinard (and later Jim Meyering), are distributed in Automake's hand-written @file{aclocal.m4} file. Package maintainers are expected to extract the necessary macros from this file. (In previous versions you had to copy and paste them from the manual...) @item 1996-03-11 Automake 0.31 The test suite in 0.30 was run via a long @code{check-local} rule. Upon Ulrich Drepper's suggestion, 0.31 makes it an Automake rule output whenever the @code{TESTS} variable is defined. @code{DIST_OTHER} is renamed to @code{EXTRA_DIST}, and the @code{check_} prefix is introduced. The syntax is now the same as today. @item 1996-03-15 Gordon Matzigkeit starts writing libtool. @item 1996-04-27 Automake 0.32 @code{-hook} targets are introduced; an idea from Dieter Baron. @file{*.info} files, which were output in the build directory are now built in the source directory, because they are distributed. It seems these files like to move back and forth as that will happen again in future versions. @item 1996-05-18 Automake 0.33 Gord Matzigkeit's main two contributions: @itemize @item very preliminary libtool support @item the distcheck rule @end itemize Although they were very basic at this point, these are probably among the top features for Automake today. Jim Meyering also provides the infamous @code{jm_MAINTAINER_MODE}, since then renamed to @code{AM_MAINTAINER_MODE} and abandoned by its author (@pxref{maintainer-mode, , maintainer-mode, automake, GNU Automake}). @item 1996-05-28 Automake 1.0 After only six months of heavy development, the @command{automake} script is 3134 lines long, plus 973 lines of @file{Makefile} fragments. The package has 30 pages of documentation, and 38 test cases. @file{aclocal.m4} contains 4 macros. From now on and until version 1.4, new releases will occur at a rate of about one a year. 1.1 did not exist, actually 1.1b to 1.1p have been the name of beta releases for 1.2. This is the first time Automake uses suffix letters to designate beta releases, a habit that lasts. @item 1996-10-10 Kevin Dalley packages Automake 1.0 for Debian GNU/Linux. @item 1996-11-26 David J.@tie{}MacKenzie releases Autoconf 2.12. Between June and October, the Autoconf development is almost stalled. Roland McGrath has been working at the beginning of the year. David comes back in November to release 2.12, but he won't touch Autoconf anymore after this year, and Autoconf then really stagnates. The desolate Autoconf @file{ChangeLog} for 1997 lists only 7 commits. @item 1997-02-28 @email{automake@@gnu.ai.mit.edu} list alive The mailing list is announced as follows: @smallexample I've created the "automake" mailing list. It is "automake@@gnu.ai.mit.edu". Administrivia, as always, to automake-request@@gnu.ai.mit.edu. The charter of this list is discussion of automake, autoconf, and other configuration/portability tools (e.g., libtool). It is expected that discussion will range from pleas for help all the way up to patches. This list is archived on the FSF machines. Offhand I don't know if you can get the archive without an account there. This list is open to anybody who wants to join. Tell all your friends! -- Tom Tromey @end smallexample Before that people were discussing Automake privately, on the Gnits mailing list (which is not public either), and less frequently on @code{gnu.misc.discuss}. @code{gnu.ai.mit.edu} is now @code{gnu.org}, in case you never noticed. The archives of the early years of the @code{automake@@gnu.org} list have been lost, so today it is almost impossible to find traces of discussions that occurred before 1999. This has been annoying more than once, as such discussions can be useful to understand the rationale behind a piece of uncommented code that was introduced back then. @item 1997-06-22 Automake 1.2 Automake developments continues, and more and more new Autoconf macros are required. Distributing them in @file{aclocal.m4} and requiring people to browse this file to extract the relevant macros becomes uncomfortable. Ideally, some of them should be contributed to Autoconf so that they can be used directly, however Autoconf is currently inactive. Automake 1.2 consequently introduces @command{aclocal} (@command{aclocal} was actually started on 1996-07-28), a tool that automatically constructs an @file{aclocal.m4} file from a repository of third-party macros. Because Autoconf has stalled, Automake also becomes a kind of repository for such third-party macros, even macros completely unrelated to Automake (for instance macros that fix broken Autoconf macros). The 1.2 release contains 20 macros, including the @code{AM_INIT_AUTOMAKE} macro that simplifies the creation of @file{configure.in}. Libtool is fully supported using @code{*_LTLIBRARIES}. The missing script is introduced by Fran@,cois Pinard; it is meant to be a better solution than @code{AM_MAINTAINER_MODE} (@pxref{maintainer-mode, , maintainer-mode, automake, GNU Automake}). Conditionals support was implemented by Ian Lance Taylor. At the time, Tom and Ian were working on an internal project at Cygnus. They were using ILU, which is pretty similar to CORBA@. They wanted to integrate ILU into their build, which was all @file{configure}-based, and Ian thought that adding conditionals to @command{automake} was simpler than doing all the work in @file{configure} (which was the standard at the time). So this was actually funded by Cygnus. This very useful but tricky feature will take a lot of time to stabilize. (At the time this text is written, there are still primaries that have not been updated to support conditional definitions in Automake 1.9.) The @command{automake} script has almost doubled: 6089 lines of Perl, plus 1294 lines of @file{Makefile} fragments. @item 1997-07-08 Gordon Matzigkeit releases Libtool 1.0. @item 1998-04-05 Automake 1.3 This is a small advance compared to 1.2. It adds support for assembly, and preliminary support for Java. Perl 5.004_04 is out, but fixes to support Perl 4 are still regularly submitted whenever Automake breaks it. @item 1998-09-06 @code{sourceware.cygnus.com} is on-line. Sourceware was setup by Jason Molenda to host open source projects. @item 1998-09-19 Automake CVS repository moved to @code{sourceware.cygnus.com} @itemx 1998-10-26 @code{sourceware.cygnus.com} announces it hosts Automake: Automake is now hosted on @code{sourceware.cygnus.com}. It has a publicly accessible CVS repository. This CVS repository is a copy of the one Tom was using on his machine, which in turn is based on a copy of the CVS repository of David MacKenzie. This is why we still have to full source history. (Automake was on Sourceware until 2007-10-29, when it moved to a git repository on @code{savannah.gnu.org}, but the Sourceware host had been renamed to @code{sources.redhat.com}.) The oldest file in the administrative directory of the CVS repository that was created on Sourceware is dated 1998-09-19, while the announcement that @command{automake} and @command{autoconf} had joined @command{sourceware} was made on 1998-10-26. They were among the first projects to be hosted there. The heedful reader will have noticed Automake was exactly 4 years old on 1998-09-19. @item 1999-01-05 Ben Elliston releases Autoconf 2.13. @item 1999-01-14 Automake 1.4 This release adds support for Fortran 77 and for the @code{include} statement. Also, @samp{+=} assignments are introduced, but it is still quite easy to fool Automake when mixing this with conditionals. These two releases, Automake 1.4 and Autoconf 2.13 make a duo that will be used together for years. @command{automake} is 7228 lines, plus 1591 lines of Makefile fragment, 20 macros (some 1.3 macros were finally contributed back to Autoconf), 197 test cases, and 51 pages of documentation. @item 1999-03-27 The @code{user-dep-branch} is created on the CVS repository. This implements a new dependency tracking schemed that should be able to handle automatic dependency tracking using any compiler (not just gcc) and any make (not just GNU @command{make}). In addition, the new scheme should be more reliable than the old one, as dependencies are generated on the end user's machine. Alexandre Oliva creates depcomp for this purpose. @xref{Dependency Tracking Evolution}, for more details about the evolution of automatic dependency tracking in Automake. @item 1999-11-21 The @code{user-dep-branch} is merged into the main trunk. This was a huge problem since we also had patches going in on the trunk. The merge took a long time and was very painful. @item 2000-05-10 Since September 1999 and until 2003, Akim Demaille will be zealously revamping Autoconf. @quotation I think the next release should be called "3.0".@* Let's face it: you've basically rewritten autoconf.@* Every weekend there are 30 new patches.@* I don't see how we could call this "2.15" with a straight face.@* -- Tom Tromey on @email{autoconf@@gnu.org} @end quotation Actually Akim works like a submarine: he will pile up patches while he works off-line during the weekend, and flush them in batch when he resurfaces on Monday. @item 2001-01-24 On this Wednesday, Autoconf 2.49c, the last beta before Autoconf 2.50 is out, and Akim has to find something to do during his week-end :) @item 2001-01-28 Akim sends a batch of 14 patches to @email{automake@@gnu.org}. @quotation Aiieeee! I was dreading the day that the Demaillator turned his sights on automake@dots{} and now it has arrived! -- Tom Tromey @end quotation It's only the beginning: in two months he will send 192 patches. Then he would slow down so Tom can catch up and review all this. Initially Tom actually read all of these patches, then he probably trustingly answered OK to most of them, and finally gave up and let Akim apply whatever he wanted. There was no way to keep up with that patch rate. @quotation Anyway the patch below won't apply since it predates Akim's sourcequake; I have yet to figure where the relevant passage has been moved :) -- Alexandre Duret-Lutz @end quotation All of these patches were sent to and discussed on @email{automake@@gnu.org}, so subscribed users were literally drowning in technical mails. Eventually, the @email{automake-patches@@gnu.org} mailing list was created in May. Year after year, Automake had drifted away from its initial design: construct @file{Makefile.in} by assembling various @file{Makefile} fragments. In 1.4, lots of @file{Makefile} rules are being emitted at various places in the @command{automake} script itself; this does not help ensuring a consistent treatment of these rules (for instance making sure that user-defined rules override Automake's own rules). One of Akim's goal was moving all of these hard-coded rules to separate @file{Makefile} fragments, so the logic could be centralized in a @file{Makefile} fragment processor. Another significant contribution of Akim is the interface with the ``trace'' feature of Autoconf. The way to scan @file{configure.in} at this time was to read the file and grep the various macro of interest to Automake. Doing so could break in many unexpected ways; @command{automake} could miss some definition (for instance @samp{AC_SUBST([$1], [$2])} where the arguments are known only when M4 is run), or conversely it could detect some macro that was not expanded (because it is called conditionally). In the CVS version of Autoconf, Akim had implemented the @option{--trace} option, which provides accurate information about where macros are actually called and with what arguments. Akim will equip Automake with a second @file{configure.in} scanner that uses this @option{--trace} interface. Since it was not sensible to drop the Autoconf 2.13 compatibility yet, this experimental scanner was only used when an environment variable was set, the traditional grep-scanner being still the default. @item 2001-04-25 Gary V.@tie{}Vaughan releases Libtool 1.4 It has been more than two years since Automake 1.4, CVS Automake has suffered lot's of heavy changes and still is not ready for release. Libtool 1.4 had to be distributed with a patch against Automake 1.4. @item 2001-05-08 Automake 1.4-p1 @itemx 2001-05-24 Automake 1.4-p2 Gary V.@tie{}Vaughan, the principal Libtool maintainer, makes a ``patch release'' of Automake: @quotation The main purpose of this release is to have a stable automake which is compatible with the latest stable libtool. @end quotation The release also contains obvious fixes for bugs in Automake 1.4, some of which were reported almost monthly. @item 2001-05-21 Akim Demaille releases Autoconf 2.50 @item 2001-06-07 Automake 1.4-p3 @itemx 2001-06-10 Automake 1.4-p4 @itemx 2001-07-15 Automake 1.4-p5 Gary continues his patch-release series. These also add support for some new Autoconf 2.50 idioms. Essentially, Autoconf now advocates @file{configure.ac} over @file{configure.in}, and it introduces a new syntax for @code{AC_OUTPUT}ing files. @item 2001-08-23 Automake 1.5 A major and long-awaited release, that comes more than two years after 1.4. It brings many changes, among which: @itemize @item The new dependency tracking scheme that uses @command{depcomp}. Aside from the improvement on the dependency tracking itself (@pxref{Dependency Tracking Evolution}), this also streamlines the use of @command{automake}-generated @file{Makefile.in}s as the @file{Makefile.in}s used during development are now the same as those used in distributions. Before that the @file{Makefile.in}s generated for maintainers required GNU @command{make} and GCC, they were different from the portable @file{Makefile} generated for distribution; this was causing some confusion. @item Support for per-target compilation flags. @item Support for reference to files in subdirectories in most @file{Makefile.am} variables. @item Introduction of the @code{dist_}, @code{nodist_}, and @code{nobase_} prefixes. @item Perl 4 support is finally dropped. @end itemize 1.5 did break several packages that worked with 1.4. Enough so that Linux distributions could not easily install the new Automake version without breaking many of the packages for which they had to run @command{automake}. Some of these breakages were effectively bugs that would eventually be fixed in the next release. However, a lot of damage was caused by some changes made deliberately to render Automake stricter on some setup we did consider bogus. For instance, @samp{make distcheck} was improved to check that @samp{make uninstall} did remove all the files @samp{make install} installed, that @samp{make distclean} did not omit some file, and that a VPATH build would work even if the source directory was read-only. Similarly, Automake now rejects multiple definitions of the same variable (because that would mix very badly with conditionals), and @samp{+=} assignments with no previous definition. Because these changes all occurred suddenly after 1.4 had been established for more than two years, it hurt users. To make matter worse, meanwhile Autoconf (now at version 2.52) was facing similar troubles, for similar reasons. @item 2002-03-05 Automake 1.6 This release introduced versioned installation (@pxref{API Versioning, , API Versioning, automake, GNU Automake}). This was mainly pushed by Havoc Pennington, taking the GNOME source tree as motive: due to incompatibilities between the autotools it's impossible for the GNOME packages to switch to Autoconf 2.53 and Automake 1.5 all at once, so they are currently stuck with Autoconf 2.13 and Automake 1.4. The idea was to call this version @file{automake-1.6}, call all its bug-fix versions identically, and switch to @file{automake-1.7} for the next release that adds new features or changes some rules. This scheme implies maintaining a bug-fix branch in addition to the development trunk, which means more work from the maintainer, but providing regular bug-fix releases proved to be really worthwhile. Like 1.5, 1.6 also introduced a bunch of incompatibilities, intentional or not. Perhaps the more annoying was the dependence on the newly released Autoconf 2.53. Autoconf seemed to have stabilized enough since its explosive 2.50 release and included changes required to fix some bugs in Automake. In order to upgrade to Automake 1.6, people now had to upgrade Autoconf too; for some packages it was no picnic. While versioned installation helped people to upgrade, it also unfortunately allowed people not to upgrade. At the time of writing, some Linux distributions are shipping packages for Automake 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Most of these still install 1.4 by default. Some distribution also call 1.4 the ``stable'' version, and present ``1.9'' as the development version; this does not really makes sense since 1.9 is way more solid than 1.4. All this does not help the newcomer. @item 2002-04-11 Automake 1.6.1 1.6, and the upcoming 1.4-p6 release were the last release by Tom. This one and those following will be handled by Alexandre Duret-Lutz. Tom is still around, and will be there until about 1.7, but his interest into Automake is drifting away towards projects like @command{gcj}. Alexandre has been using Automake since 2000, and started to contribute mostly on Akim's incitement (Akim and Alexandre have been working in the same room from 1999 to 2002). In 2001 and 2002 he had a lot of free time to enjoy hacking Automake. @item 2002-06-14 Automake 1.6.2 @item 2002-07-28 Automake 1.6.3 @itemx 2002-07-28 Automake 1.4-p6 Two releases on the same day. 1.6.3 is a bug-fix release. Tom Tromey backported the versioned installation mechanism on the 1.4 branch, so that Automake 1.6.x and Automake 1.4-p6 could be installed side by side. Another request from the GNOME folks. @item 2002-09-25 Automake 1.7 This release switches to the new @file{configure.ac} scanner Akim was experimenting in 1.5. @item 2002-10-16 Automake 1.7.1 @itemx 2002-12-06 Automake 1.7.2 @itemx 2003-02-20 Automake 1.7.3 @itemx 2003-04-23 Automake 1.7.4 @itemx 2003-05-18 Automake 1.7.5 @itemx 2003-07-10 Automake 1.7.6 @itemx 2003-09-07 Automake 1.7.7 @itemx 2003-10-07 Automake 1.7.8 Many bug-fix releases. 1.7 lasted because the development version (upcoming 1.8) was suffering some major internal revamping. @item 2003-10-26 Automake on screen Episode 49, `Repercussions', in the third season of the `Alias' TV show is first aired. Marshall, one of the characters, is working on a computer virus that he has to modify before it gets into the wrong hands or something like that. The screenshots you see do not show any program code, they show a @file{Makefile.in} generated by automake... @item 2003-11-09 Automake 1.7.9 @item 2003-12-10 Automake 1.8 The most striking update is probably that of @command{aclocal}. @command{aclocal} now uses @code{m4_include} in the produced @file{aclocal.m4} when the included macros are already distributed with the package (an idiom used in many packages), which reduces code duplication. Many people liked that, but in fact this change was really introduced to fix a bug in rebuild rules: @file{Makefile.in} must be rebuilt whenever a dependency of @file{configure} changes, but all the @file{m4} files included in @file{aclocal.m4} where unknown from @command{automake}. Now @command{automake} can just trace the @code{m4_include}s to discover the dependencies. @command{aclocal} also starts using the @option{--trace} Autoconf option in order to discover used macros more accurately. This will turn out to be very tricky (later releases will improve this) as people had devised many ways to cope with the limitation of previous @command{aclocal} versions, notably using handwritten @code{m4_include}s: @command{aclocal} must make sure not to redefine a rule that is already included by such statement. Automake also has seen its guts rewritten. Although this rewriting took a lot of efforts, it is only apparent to the users in that some constructions previously disallowed by the implementation now work nicely. Conditionals, Locations, Variable and Rule definitions, Options: these items on which Automake works have been rewritten as separate Perl modules, and documented. @item 2004-01-11 Automake 1.8.1 @itemx 2004-01-12 Automake 1.8.2 @itemx 2004-03-07 Automake 1.8.3 @itemx 2004-04-25 Automake 1.8.4 @itemx 2004-05-16 Automake 1.8.5 @item 2004-07-28 Automake 1.9 This release tries to simplify the compilation rules it outputs to reduce the size of the Makefile. The complaint initially come from the libgcj developers. Their @file{Makefile.in} generated with Automake 1.4 and custom build rules (1.4 did not support compiled Java) is 250KB@. The one generated by 1.8 was over 9MB@! 1.9 gets it down to 1.2MB@. Aside from this it contains mainly minor changes and bug-fixes. @item 2004-08-11 Automake 1.9.1 @itemx 2004-09-19 Automake 1.9.2 Automake has ten years. This chapter of the manual was initially written for this occasion. @item 2007-10-29 Automake repository moves to @code{savannah.gnu.org} and uses git as primary repository. @end table @node Dependency Tracking Evolution @chapter Evolution of Automatic Dependency Tracking Over the years Automake has deployed three different dependency tracking methods. Each method, including the current one, has had flaws of various sorts. Here we lay out the different dependency tracking methods, their flaws, and their fixes. We conclude with recommendations for tool writers, and by indicating future directions for dependency tracking work in Automake. @menu * First Take on Dependencies:: Precomputed dependency tracking * Dependencies As Side Effects:: Update at developer compile time * Dependencies for the User:: Update at user compile time * Techniques for Dependencies:: Alternative approaches @end menu @node First Take on Dependencies @section First Take on Dependency Tracking @unnumberedsubsec Description Our first attempt at automatic dependency tracking was based on the method recommended by GNU @command{make}. (@pxref{Automatic Prerequisites, , Generating Prerequisites Automatically, make, The GNU make Manual}) This version worked by precomputing dependencies ahead of time. For each source file, it had a special @file{.P} file that held the dependencies. There was a rule to generate a @file{.P} file by invoking the compiler appropriately. All such @file{.P} files were included by the @file{Makefile}, thus implicitly becoming dependencies of @file{Makefile}. @unnumberedsubsec Bugs This approach had several critical bugs. @itemize @item The code to generate the @file{.P} file relied on @command{gcc}. (A limitation, not technically a bug.) @item The dependency tracking mechanism itself relied on GNU @command{make}. (A limitation, not technically a bug.) @item Because each @file{.P} file was a dependency of @file{Makefile}, this meant that dependency tracking was done eagerly by @command{make}. For instance, @samp{make clean} would cause all the dependency files to be updated, and then immediately removed. This eagerness also caused problems with some configurations; if a certain source file could not be compiled on a given architecture for some reason, dependency tracking would fail, aborting the entire build. @item As dependency tracking was done as a pre-pass, compile times were doubled--the compiler had to be run twice per source file. @item @samp{make dist} re-ran @command{automake} to generate a @file{Makefile} that did not have automatic dependency tracking (and that was thus portable to any version of @command{make}). In order to do this portably, Automake had to scan the dependency files and remove any reference that was to a source file not in the distribution. This process was error-prone. Also, if @samp{make dist} was run in an environment where some object file had a dependency on a source file that was only conditionally created, Automake would generate a @file{Makefile} that referred to a file that might not appear in the end user's build. A special, hacky mechanism was required to work around this. @end itemize @unnumberedsubsec Historical Note The code generated by Automake is often inspired by the @file{Makefile} style of a particular author. In the case of the first implementation of dependency tracking, I believe the impetus and inspiration was Jim Meyering. (I could be mistaken. If you know otherwise feel free to correct me.) @node Dependencies As Side Effects @section Dependencies As Side Effects @unnumberedsubsec Description The next refinement of Automake's automatic dependency tracking scheme was to implement dependencies as side effects of the compilation. This was aimed at solving the most commonly reported problems with the first approach. In particular we were most concerned with eliminating the weird rebuilding effect associated with make clean. In this approach, the @file{.P} files were included using the @code{-include} command, which let us create these files lazily. This avoided the @samp{make clean} problem. We only computed dependencies when a file was actually compiled. This avoided the performance penalty associated with scanning each file twice. It also let us avoid the other problems associated with the first, eager, implementation. For instance, dependencies would never be generated for a source file that was not compilable on a given architecture (because it in fact would never be compiled). @unnumberedsubsec Bugs @itemize @item This approach also relied on the existence of @command{gcc} and GNU @command{make}. (A limitation, not technically a bug.) @item Dependency tracking was still done by the developer, so the problems from the first implementation relating to massaging of dependencies by @samp{make dist} were still in effect. @item This implementation suffered from the ``deleted header file'' problem. Suppose a lazily-created @file{.P} file includes a dependency on a given header file, like this: @example maude.o: maude.c something.h @end example Now suppose that you remove @file{something.h} and update @file{maude.c} so that this include is no longer needed. If you run @command{make}, you will get an error because there is no way to create @file{something.h}. We fixed this problem in a later release by further massaging the output of @command{gcc} to include a dummy dependency for each header file. @end itemize @node Dependencies for the User @section Dependencies for the User @unnumberedsubsec Description The bugs associated with @samp{make dist}, over time, became a real problem. Packages using Automake were being built on a large number of platforms, and were becoming increasingly complex. Broken dependencies were distributed in ``portable'' @file{Makefile.in}s, leading to user complaints. Also, the requirement for @command{gcc} and GNU @command{make} was a constant source of bug reports. The next implementation of dependency tracking aimed to remove these problems. We realized that the only truly reliable way to automatically track dependencies was to do it when the package itself was built. This meant discovering a method portable to any version of make and any compiler. Also, we wanted to preserve what we saw as the best point of the second implementation: dependency computation as a side effect of compilation. In the end we found that most modern make implementations support some form of include directive. Also, we wrote a wrapper script that let us abstract away differences between dependency tracking methods for compilers. For instance, some compilers cannot generate dependencies as a side effect of compilation. In this case we simply have the script run the compiler twice. Currently our wrapper script (@command{depcomp}) knows about twelve different compilers (including a "compiler" that simply invokes @command{makedepend} and then the real compiler, which is assumed to be a standard Unix-like C compiler with no way to do dependency tracking). @unnumberedsubsec Bugs @itemize @item Running a wrapper script for each compilation slows down the build. @item Many users don't really care about precise dependencies. @item This implementation, like every other automatic dependency tracking scheme in common use today (indeed, every one we've ever heard of), suffers from the ``duplicated new header'' bug. This bug occurs because dependency tracking tools, such as the compiler, only generate dependencies on the successful opening of a file, and not on every probe. Suppose for instance that the compiler searches three directories for a given header, and that the header is found in the third directory. If the programmer erroneously adds a header file with the same name to the first directory, then a clean rebuild from scratch could fail (suppose the new header file is buggy), whereas an incremental rebuild will succeed. What has happened here is that people have a misunderstanding of what a dependency is. Tool writers think a dependency encodes information about which files were read by the compiler. However, a dependency must actually encode information about what the compiler tried to do. This problem is not serious in practice. Programmers typically do not use the same name for a header file twice in a given project. (At least, not in C or C++. This problem may be more troublesome in Java.) This problem is easy to fix, by modifying dependency generators to record every probe, instead of every successful open. @item Since Automake generates dependencies as a side effect of compilation, there is a bootstrapping problem when header files are generated by running a program. The problem is that, the first time the build is done, there is no way by default to know that the headers are required, so make might try to run a compilation for which the headers have not yet been built. This was also a problem in the previous dependency tracking implementation. The current fix is to use @code{BUILT_SOURCES} to list built headers (@pxref{Sources, , Sources, automake, GNU Automake}). This causes them to be built before any other build rules are run. This is unsatisfactory as a general solution, however in practice it seems sufficient for most actual programs. @end itemize This code is used since Automake 1.5. In GCC 3.0, we managed to convince the maintainers to add special command-line options to help Automake more efficiently do its job. We hoped this would let us avoid the use of a wrapper script when Automake's automatic dependency tracking was used with @command{gcc}. Unfortunately, this code doesn't quite do what we want. In particular, it removes the dependency file if the compilation fails; we'd prefer that it instead only touch the file in any way if the compilation succeeds. Nevertheless, since Automake 1.7, when a recent @command{gcc} is detected at @command{configure} time, we inline the dependency-generation code and do not use the @command{depcomp} wrapper script. This makes compilations faster for those using this compiler (probably our primary user base). The counterpart is that because we have to encode two compilation rules in @file{Makefile} (with or without @command{depcomp}), the produced @file{Makefile}s are larger. @node Techniques for Dependencies @section Techniques for Computing Dependencies There are actually several ways for a build tool like Automake to cause tools to generate dependencies. @table @asis @item @command{makedepend} This was a commonly-used method in the past. The idea is to run a special program over the source and have it generate dependency information. Traditional implementations of @command{makedepend} are not completely precise; ordinarily they were conservative and discovered too many dependencies. @item The tool An obvious way to generate dependencies is to simply write the tool so that it can generate the information needed by the build tool. This is also the most portable method. Many compilers have an option to generate dependencies. Unfortunately, not all tools provide such an option. @item The file system It is possible to write a special file system that tracks opens, reads, writes, etc, and then feed this information back to the build tool. @command{clearmake} does this. This is a very powerful technique, as it doesn't require cooperation from the tool. Unfortunately it is also very difficult to implement and also not practical in the general case. @item @code{LD_PRELOAD} Rather than use the file system, one could write a special library to intercept @code{open} and other syscalls. This technique is also quite powerful, but unfortunately it is not portable enough for use in @command{automake}. @end table @menu * Recommendations for Tool Writers:: * Future Directions for Dependencies:: @end menu @node Recommendations for Tool Writers @subsection Recommendations for Tool Writers We think that every compilation tool ought to be able to generate dependencies as a side effect of compilation. Furthermore, at least while @command{make}-based tools are nearly universally in use (at least in the free software community), the tool itself should generate dummy dependencies for header files, to avoid the deleted header file bug. Finally, the tool should generate a dependency for each probe, instead of each successful file open, in order to avoid the duplicated new header bug. @node Future Directions for Dependencies @subsection Future Directions for Dependencies Currently, only languages and compilers understood by Automake can have dependency tracking enabled. We would like to see if it is practical (and worthwhile) to let this support be extended by the user to languages unknown to Automake. @node Releases @chapter Release Statistics The following table (inspired by @samp{perlhist(1)}) quantifies the evolution of Automake using these metrics: @table @asis @item Date, Rel The date and version of the release. @item am The number of lines of the @command{automake} script. @item acl The number of lines of the @command{aclocal} script. @item pm The number of lines of the @command{Perl} supporting modules. @item @file{*.am} The number of lines of the @file{Makefile} fragments. The number in parentheses is the number of files. @item m4 The number of lines (and files) of Autoconf macros. @item doc The number of pages of the documentation (the Postscript version). @item t The number of test cases in the test suite. Of those, the number in parentheses is the number of generated test cases. @end table @multitable {8888-88-88} {8.8-p8} {8888} {8888} {8888} {8888 (88)} {8888 (88)} {888} {888 (88)} @headitem Date @tab Rel @tab am @tab acl @tab pm @tab @file{*.am} @tab m4 @tab doc @tab t @item 1994-09-19 @tab CVS @tab 141 @tab @tab @tab 299 (24) @tab @tab @tab @item 1994-11-05 @tab CVS @tab 208 @tab @tab @tab 332 (28) @tab @tab @tab @item 1995-11-23 @tab 0.20 @tab 533 @tab @tab @tab 458 (35) @tab @tab 9 @tab @item 1995-11-26 @tab 0.21 @tab 613 @tab @tab @tab 480 (36) @tab @tab 11 @tab @item 1995-11-28 @tab 0.22 @tab 1116 @tab @tab @tab 539 (38) @tab @tab 12 @tab @item 1995-11-29 @tab 0.23 @tab 1240 @tab @tab @tab 541 (38) @tab @tab 12 @tab @item 1995-12-08 @tab 0.24 @tab 1462 @tab @tab @tab 504 (33) @tab @tab 14 @tab @item 1995-12-10 @tab 0.25 @tab 1513 @tab @tab @tab 511 (37) @tab @tab 15 @tab @item 1996-01-03 @tab 0.26 @tab 1706 @tab @tab @tab 438 (36) @tab @tab 16 @tab @item 1996-01-03 @tab 0.27 @tab 1706 @tab @tab @tab 438 (36) @tab @tab 16 @tab @item 1996-01-13 @tab 0.28 @tab 1964 @tab @tab @tab 934 (33) @tab @tab 16 @tab @item 1996-02-07 @tab 0.29 @tab 2299 @tab @tab @tab 936 (33) @tab @tab 17 @tab @item 1996-02-24 @tab 0.30 @tab 2544 @tab @tab @tab 919 (32) @tab 85 (1) @tab 20 @tab 9 @item 1996-03-11 @tab 0.31 @tab 2877 @tab @tab @tab 919 (32) @tab 85 (1) @tab 29 @tab 17 @item 1996-04-27 @tab 0.32 @tab 3058 @tab @tab @tab 921 (31) @tab 85 (1) @tab 30 @tab 26 @item 1996-05-18 @tab 0.33 @tab 3110 @tab @tab @tab 926 (31) @tab 105 (1) @tab 30 @tab 35 @item 1996-05-28 @tab 1.0 @tab 3134 @tab @tab @tab 973 (32) @tab 105 (1) @tab 30 @tab 38 @item 1997-06-22 @tab 1.2 @tab 6089 @tab 385 @tab @tab 1294 (36) @tab 592 (20) @tab 37 @tab 126 @item 1998-04-05 @tab 1.3 @tab 6415 @tab 422 @tab @tab 1470 (39) @tab 741 (23) @tab 39 @tab 156 @item 1999-01-14 @tab 1.4 @tab 7240 @tab 426 @tab @tab 1591 (40) @tab 734 (20) @tab 51 @tab 197 @item 2001-05-08 @tab 1.4-p1 @tab 7251 @tab 426 @tab @tab 1591 (40) @tab 734 (20) @tab 51 @tab 197 @item 2001-05-24 @tab 1.4-p2 @tab 7268 @tab 439 @tab @tab 1591 (40) @tab 734 (20) @tab 49 @tab 197 @item 2001-06-07 @tab 1.4-p3 @tab 7312 @tab 439 @tab @tab 1591 (40) @tab 734 (20) @tab 49 @tab 197 @item 2001-06-10 @tab 1.4-p4 @tab 7321 @tab 439 @tab @tab 1591 (40) @tab 734 (20) @tab 49 @tab 198 @item 2001-07-15 @tab 1.4-p5 @tab 7228 @tab 426 @tab @tab 1596 (40) @tab 734 (20) @tab 51 @tab 198 @item 2001-08-23 @tab 1.5 @tab 8016 @tab 475 @tab 600 @tab 2654 (39) @tab 1166 (29) @tab 63 @tab 327 @item 2002-03-05 @tab 1.6 @tab 8465 @tab 475 @tab 1136 @tab 2732 (39) @tab 1603 (27) @tab 66 @tab 365 @item 2002-04-11 @tab 1.6.1 @tab 8544 @tab 475 @tab 1136 @tab 2741 (39) @tab 1603 (27) @tab 66 @tab 372 @item 2002-06-14 @tab 1.6.2 @tab 8575 @tab 475 @tab 1136 @tab 2800 (39) @tab 1609 (27) @tab 67 @tab 386 @item 2002-07-28 @tab 1.6.3 @tab 8600 @tab 475 @tab 1153 @tab 2809 (39) @tab 1609 (27) @tab 67 @tab 391 @item 2002-07-28 @tab 1.4-p6 @tab 7332 @tab 455 @tab @tab 1596 (40) @tab 735 (20) @tab 49 @tab 197 @item 2002-09-25 @tab 1.7 @tab 9189 @tab 471 @tab 1790 @tab 2965 (39) @tab 1606 (28) @tab 73 @tab 430 @item 2002-10-16 @tab 1.7.1 @tab 9229 @tab 475 @tab 1790 @tab 2977 (39) @tab 1606 (28) @tab 73 @tab 437 @item 2002-12-06 @tab 1.7.2 @tab 9334 @tab 475 @tab 1790 @tab 2988 (39) @tab 1606 (28) @tab 77 @tab 445 @item 2003-02-20 @tab 1.7.3 @tab 9389 @tab 475 @tab 1790 @tab 3023 (39) @tab 1651 (29) @tab 84 @tab 448 @item 2003-04-23 @tab 1.7.4 @tab 9429 @tab 475 @tab 1790 @tab 3031 (39) @tab 1644 (29) @tab 85 @tab 458 @item 2003-05-18 @tab 1.7.5 @tab 9429 @tab 475 @tab 1790 @tab 3033 (39) @tab 1645 (29) @tab 85 @tab 459 @item 2003-07-10 @tab 1.7.6 @tab 9442 @tab 475 @tab 1790 @tab 3033 (39) @tab 1660 (29) @tab 85 @tab 461 @item 2003-09-07 @tab 1.7.7 @tab 9443 @tab 475 @tab 1790 @tab 3041 (39) @tab 1660 (29) @tab 90 @tab 467 @item 2003-10-07 @tab 1.7.8 @tab 9444 @tab 475 @tab 1790 @tab 3041 (39) @tab 1660 (29) @tab 90 @tab 468 @item 2003-11-09 @tab 1.7.9 @tab 9444 @tab 475 @tab 1790 @tab 3048 (39) @tab 1660 (29) @tab 90 @tab 468 @item 2003-12-10 @tab 1.8 @tab 7171 @tab 585 @tab 7730 @tab 3236 (39) @tab 1666 (31) @tab 104 @tab 521 @item 2004-01-11 @tab 1.8.1 @tab 7217 @tab 663 @tab 7726 @tab 3287 (39) @tab 1686 (31) @tab 104 @tab 525 @item 2004-01-12 @tab 1.8.2 @tab 7217 @tab 663 @tab 7726 @tab 3288 (39) @tab 1686 (31) @tab 104 @tab 526 @item 2004-03-07 @tab 1.8.3 @tab 7214 @tab 686 @tab 7735 @tab 3303 (39) @tab 1695 (31) @tab 111 @tab 530 @item 2004-04-25 @tab 1.8.4 @tab 7214 @tab 686 @tab 7736 @tab 3310 (39) @tab 1701 (31) @tab 112 @tab 531 @item 2004-05-16 @tab 1.8.5 @tab 7240 @tab 686 @tab 7736 @tab 3299 (39) @tab 1701 (31) @tab 112 @tab 533 @item 2004-07-28 @tab 1.9 @tab 7508 @tab 715 @tab 7794 @tab 3352 (40) @tab 1812 (32) @tab 115 @tab 551 @item 2004-08-11 @tab 1.9.1 @tab 7512 @tab 715 @tab 7794 @tab 3354 (40) @tab 1812 (32) @tab 115 @tab 552 @item 2004-09-19 @tab 1.9.2 @tab 7512 @tab 715 @tab 7794 @tab 3354 (40) @tab 1812 (32) @tab 132 @tab 554 @item 2004-11-01 @tab 1.9.3 @tab 7507 @tab 718 @tab 7804 @tab 3354 (40) @tab 1812 (32) @tab 134 @tab 556 @item 2004-12-18 @tab 1.9.4 @tab 7508 @tab 718 @tab 7856 @tab 3361 (40) @tab 1811 (32) @tab 140 @tab 560 @item 2005-02-13 @tab 1.9.5 @tab 7523 @tab 719 @tab 7859 @tab 3373 (40) @tab 1453 (32) @tab 142 @tab 562 @item 2005-07-10 @tab 1.9.6 @tab 7539 @tab 699 @tab 7867 @tab 3400 (40) @tab 1453 (32) @tab 144 @tab 570 @item 2006-10-15 @tab 1.10 @tab 7859 @tab 1072 @tab 8024 @tab 3512 (40) @tab 1496 (34) @tab 172 @tab 604 @item 2008-01-19 @tab 1.10.1 @tab 7870 @tab 1089 @tab 8025 @tab 3520 (40) @tab 1499 (34) @tab 173 @tab 617 @item 2008-11-23 @tab 1.10.2 @tab 7882 @tab 1089 @tab 8027 @tab 3540 (40) @tab 1509 (34) @tab 176 @tab 628 @item 2009-05-17 @tab 1.11 @tab 8721 @tab 1092 @tab 8289 @tab 4164 (42) @tab 1714 (37) @tab 181 @tab 732 (20) @end multitable @c ========================================================== Appendices @page @node Copying This Manual @appendix Copying This Manual @menu * GNU Free Documentation License:: License for copying this manual @end menu @node GNU Free Documentation License @appendixsec GNU Free Documentation License @include fdl.texi @bye