Major changes in release 2.13:

* Support for building on Win32 systems where the only available C or
  C++ compiler is the Microsoft Visual C++ command line compiler
  (`cl').  Additional support for building on Win32 systems which are
  using the Cygwin or Mingw32 environments.
* Support for alternative object file and executable file extensions.
  On Win32, for example, these are .obj and .exe. These are discovered
  using AC_OBJEXT and AC_EXEEXT, which substitute @OBJEXT@ and
  @EXEEXT@ in the output, respectively.
* New macros: AC_CACHE_LOAD, AC_CACHE_SAVE, AC_FUNC_SELECT_ARGTYPES,
  AC_VALIDATE_CACHED_SYSTEM_TUPLE, AC_SEARCH_LIBS, AC_TRY_LINK_FUNC,
  AC_C_STRINGIZE, AC_CHECK_FILE(S), AC_PROG_F77 (and friends).
* AC_DEFINE now has an optional third argument for a description to be
  placed in the config header input file (e.g. config.h.in).
* The C++ code fragment compiled for the C++ compiler test had to be
  improved to include an explicit return type for main(). This was
  causing failures on systems using recent versions of the EGCS C++
  compiler.
* Fixed an important bug in AC_CHECK_TYPE that would cause a configure
  script to report that `sometype_t' was present when only `type_t'
  was defined.
* Merge of the FSF version of config.guess and config.sub to modernise
  these scripts. Add support for a few new hosts in config.guess.
  Incorporate latest versions of install-sh, mkinstalldirs and
  texinfo.tex from the FSF. 
* autoreconf is capable of running automake if necessary (and
  applicable).
* Support for Fortran 77. See the Texinfo documentation for details.
* Bug fixes and workarounds for quirky bugs in vendor utilities.

Major changes in release 2.12:

* AC_OUTPUT and AC_CONFIG_HEADER can create output files by
  concatenating multiple input files separated by colons, like so:
  AC_CONFIG_HEADER(config.h:conf.pre:config.h.in:conf.post)
  AC_OUTPUT(Makefile:Makefile.in:Makefile.rules)
  The arguments may be shell variables, to compute the lists on the fly.
* AC_LINK_FILES and AC_CONFIG_SUBDIRS may be called multiple times.
* New macro AC_OUTPUT_COMMANDS adds more commands to run in config.status.
* Bug fixes.

Major changes in release 2.11:

* AC_PROG_CC and AC_PROG_CXX check whether the compiler works.
  They also default CFLAGS/CXXFLAGS to "-g -O2" for gcc, instead of "-g -O".
* AC_REPLACE_FUNCS defines HAVE_foo if the system has the function `foo'.
* AC_CONFIG_HEADER expands shell variables in its argument.
* New macros: AC_FUNC_FNMATCH, AC_FUNC_SETPGRP.
* The "checking..." messages and the source code for test programs that
  fail are saved in config.log. 
* Another workaround has been added for seds with small command length limits.
* config.sub and config.guess recognize more system types.
* Bug fixes.

Major changes in release 2.10:

* Bug fixes.
* The cache variable names used by `AC_CHECK_LIB(LIB, FUNC, ...)' has
  changed: now $ac_cv_lib_LIB_FUNC, previously $ac_cv_lib_LIB.

Major changes in releases 2.6 through 2.9:

* Bug fixes.

Major changes in release 2.5:

* New configure options --bindir, --libdir, --datadir, etc., with
  corresponding output variables.
* New macro: AC_CACHE_CHECK, to make using the cache easier.
* config.log contains the command being run as well as any output from it.
* AC_CHECK_LIB can check for libraries with "." or "/" or "+" in their name.
* AC_PROG_INSTALL doesn't cache a path to install-sh, for sharing caches.
* AC_CHECK_PROG, AC_PATH_PROG, AC_CHECK_PROGS, AC_PATH_PROGS, and
  AC_CHECK_TOOL can search a path other than $PATH.
* AC_CHECK_SIZEOF takes an optional size to use when cross-compiling.

Major changes in release 2.4:

* Fix a few bugs found by Emacs testers.

Major changes in release 2.3:

* Fix the cleanup trap in several ways.
* Handle C compilers that are picky about option placement.
* ifnames gets the version number from the right directory.

Major changes in release 2.2:

* The ifnames utility is much faster but requires a "new awk" interpreter.
* AC_CHECK_LIB and AC_HAVE_LIBRARY check and add the new
  library before existing libs, not after, in case it uses them.
* New macros: AC_FUNC_GETPGRP, AC_CHECK_TOOL.
* Lots of bug fixes.
* Many additions to the TODO file :-)

Major changes in release 2.1:

* Fix C++ problems.
* More explanations in the manual.
* Fix a spurious failure in the testsuite.
* Clarify some warning messages.
* autoreconf by default only rebuilds configure and config.h.in files
  that are older than any of their particular input files; there is a
  --force option to use after installing a new version of Autoconf.

Thanks to everybody who's submitted changes and additions to Autoconf!
I've incorporated many of them, and am still considering others for
future releases -- but I didn't want to postpone this release indefinitely.

Caution: don't indiscriminately rebuild configure scripts with
Autoconf version 2.  Some configure.in files need minor adjustments to
work with it; the documentation has a chapter on upgrading.  A few
configure.in files, including those for GNU Emacs and the GNU C
Library, need major changes because they relied on undocumented
internals of version 1.  Future releases of those packages will have
updated configure.in files.

It's best to use GNU m4 1.3 (or later) with Autoconf version 2.
Autoconf now makes heavy use of m4 diversions, which were implemented
inefficiently in GNU m4 releases before 1.3.

Major changes in release 2.0:

** New copyright terms:
* There are no restrictions on distribution or use of configure scripts.

** Documentation:
* Autoconf manual is reorganized to make information easier to find
  and has several new indexes.
* INSTALL is reorganized and clearer and is now made from Texinfo source.

** New utilities:
* autoscan to generate a preliminary configure.in for a package by
  scanning its source code for commonly used nonportable functions,
  programs, and header files.
* ifnames to list the symbols used in #if and #ifdef directives in a
  source tree.
* autoupdate to update a configure.in to use the version 2 macro names.
* autoreconf to recursively remake configure and configuration header
  files in a source tree.

** Changed utilities:
* autoheader can take pieces of acconfig.h to replace config.h.{top,bot}.
* autoconf and autoheader can look for package-local definition files
  in an alternate directory.

** New macros:
* AC_CACHE_VAL to share results of tests between configure runs.
* AC_DEFUN to define macros, automatically AC_PROVIDE them, and ensure
  that macros invoked with AC_REQUIRE don't interrupt other macros.
* AC_CONFIG_AUX_DIR, AC_CANONICAL_SYSTEM, AC_CANONICAL_HOST, AC_LINK_FILES to
  support deciding unguessable features based on the host and target types.
* AC_CONFIG_SUBDIRS to recursively configure a source tree.
* AC_ARG_PROGRAM to use the options --program-prefix,
  --program-suffix, and --program-transform-name to change the names
  of programs being installed.
* AC_PREFIX_DEFAULT to change the default installation prefix.
* AC_TRY_COMPILE to compile a test program without linking it.
* AC_CHECK_TYPE to check whether sys/types.h or stdlib.h defines a given type.
* AC_CHECK_LIB to check for a particular function and library.
* AC_MSG_CHECKING and AC_MSG_RESULT to print test results, on a single line,
  whether or not the test succeeds.  They obsolete AC_CHECKING and AC_VERBOSE.
* AC_SUBST_FILE to insert one file into another.
* AC_FUNC_MEMCMP to check whether memcmp is 8-bit clean.
* AC_FUNC_STRFTIME to find strftime even if it's in -lintl.
* AC_FUNC_GETMNTENT to find getmntent even if it's in -lsun or -lseq.
* AC_HEADER_SYS_WAIT to check whether sys/wait.h is POSIX.1 compatible.

** Changed macros:
* Many macros renamed systematically, but old names are accepted for
  backward compatibility.
* AC_OUTPUT adds the "automatically generated" comment to
  non-Makefiles where it finds @configure_input@ in an input file, to
  support files with various comment syntaxes.
* AC_OUTPUT does not replace "prefix" and "exec_prefix" in generated
  files when they are not enclosed in @ signs.
* AC_OUTPUT allows the optional environment variable CONFIG_STATUS to
  override the file name "config.status".
* AC_OUTPUT takes an optional argument for passing variables from
  configure to config.status.
* AC_OUTPUT and AC_CONFIG_HEADER allow you to override the input-file names.
* AC_OUTPUT automatically substitutes the values of CFLAGS, CXXFLAGS,
  CPPFLAGS, and LDFLAGS from the environment.
* AC_PROG_CC and AC_PROG_CXX now set CFLAGS and CXXFLAGS, respectively.
* AC_PROG_INSTALL looks for install-sh or install.sh in the directory
  specified by AC_CONFIG_AUXDIR, or srcdir or srcdir/.. or
  srcdir/../.. by default.
* AC_DEFINE, AC_DEFINE_UNQUOTED, and AC_SUBST are more robust and smaller.
* AC_DEFINE no longer prints anything, because of the new result reporting
  mechanism (AC_MSG_CHECKING and AC_MSG_RESULT).
* AC_VERBOSE pays attention to --quiet/--silent, not --verbose.
* AC_ARG_ENABLE and AC_ARG_WITH support whitespace in the arguments to
  --enable- and --with- options.
* AC_CHECK_FUNCS and AC_CHECK_HEADERS take optional shell commands to
  execute on success or failure.
* Checking for C functions in C++ works.

** Removed macros:
* AC_REMOTE_TAPE and AC_RSH removed; too specific to tar and cpio, and
  better maintained with them.
* AC_ARG_ARRAY removed because no one was likely using it.
* AC_HAVE_POUNDBANG replaced with AC_SYS_INTERPRETER, which doesn't
  take arguments, for consistency with all of the other specific checks.

** New files:
* Comes with config.sub and config.guess, and uses them optionally.
* Uses config.cache to cache test results.  An alternate cache file
  can be selected with the --cache-file=FILE option.
* Uses optional shell scripts $prefix/share/config.site and
  $prefix/etc/config.site to perform site or system specific initializations.
* configure saves compiler output to ./config.log for debugging.
* New files autoconf.m4 and autoheader.m4 load the other Autoconf macros.
* acsite.m4 is the new name for the system-wide aclocal.m4.
* Has a DejaGnu test suite.

Major changes in release 1.11:

* AC_PROG_INSTALL calls install.sh with the -c option.
* AC_SET_MAKE cleans up after itself.
* AC_OUTPUT sets prefix and exec_prefix if they weren't set already.
* AC_OUTPUT prevents shells from looking in PATH for config.status.

Plus a few other bug fixes.

Major changes in release 1.10:

* autoheader uses config.h.bot if present, analogous to config.h.top.
* AC_PROG_INSTALL looks for install.sh in srcdir or srcdir/.. and
  never uses cp.
* AC_PROG_CXX looks for cxx as a C++ compiler.

Plus several bugs fixed.

Major changes in release 1.9:

* AC_YYTEXT_POINTER replaces AC_DECLARE_YYTEXT.
* AC_SIZEOF_TYPE generates the cpp symbol name automatically,
  and autoheader generates entries for those names automatically.
* AC_FIND_X gets the result from xmkmf correctly.
* AC_FIND_X assumes no X if --without-x was given.
* AC_FIND_XTRA adds libraries to the variable X_EXTRA_LIBS.
* AC_PROG_INSTALL finds OSF/1 installbsd.

Major changes in release 1.8:

** New macros:
* New macros AC_LANG_C, AC_LANG_CPLUSPLUS, AC_LANG_SAVE, AC_LANG_RESTORE,
  AC_PROG_CXX, AC_PROG_CXXCPP, AC_REQUIRE_CPP
  for checking both C++ and C features in one configure script.
* New macros AC_CHECKING, AC_VERBOSE, AC_WARN, AC_ERROR for printing messages.
* New macros AC_FIND_XTRA, AC_MMAP, AC_SIZEOF_TYPE, AC_PREREQ,
  AC_SET_MAKE, AC_ENABLE.

** Changed macros:
* AC_FIND_X looks for X in more places.
* AC_PROG_INSTALL defaults to install.sh instead of cp, if it's in srcdir.
  install.sh is distributed with Autoconf.
* AC_DECLARE_YYTEXT has been removed because it can't work, pending
  a rewrite of quoting in AC_DEFINE.
* AC_OUTPUT adds its comments in C format when substituting in C files.
* AC_COMPILE_CHECK protects its ECHO-TEXT argument with double quotes.

** New or changed command line options:
* configure accepts --enable-FEATURE[=ARG] and --disable-FEATURE options.
* configure accepts --without-PACKAGE, which sets withval=no.
* configure accepts --x-includes=DIR and --x-libraries=DIR.
* Giving --with-PACKAGE no argument sets withval=yes instead of withval=1.
* configure accepts --help, --version, --silent/--quiet, --no-create options.
* configure accepts and ignores most other Cygnus configure options, and
  warns about unknown options.
* config.status accepts --help, --version options.

** Paths and other changes:
* Relative srcdir values are not made absolute.
* The values of @prefix@ and @exec_prefix@ and @top_srcdir@ get substituted.
* Autoconf library files are installed in ${datadir}/autoconf, not ${datadir}.
* autoheader optionally copies config.h.top to the beginning of config.h.in.
* The example Makefile dependencies for configure et al. work better.
* Namespace cleanup: all shell variables used internally by Autoconf
  have names beginning with `ac_'.

More big improvements are in process for future releases, but have not
yet been (variously) finished, integrated, tested, or documented enough
to release yet.

Major changes in release 1.7:

* New macro AC_OBSOLETE.
* Bugs in Makefile.in fixed.
* AC_LONG_FILE_NAMES improved.

Major changes in release 1.6:

* New macro AC_LONG_64_BITS.
* Multiple .h files can be created.
* AC_FIND_X looks for X files directly if it doesn't find xmkmf.
* AC_ALLOCA defines C_ALLOCA if using alloca.c.
* --with-NAME can take a value, e.g., --with-targets=sun4,hp300bsd.
* Unused --no-create option to configure removed.
* autoheader doesn't change the timestamp of its output file if
  the file didn't change.
* All macros that look for libraries now use AC_HAVE_LIBRARY.
* config.status checks three optional environment variables to
  modify its behavior.
* The usual bug fixes.

Major changes in release 1.5:

* New macros AC_FIND_X, AC_OFF_T, AC_STAT_MACROS_BROKEN, AC_REVISION.
* autoconf and autoheader scripts have GNU standards conforming
  --version and --help options (they print their message and exit).
* Many bug fixes.

Major changes in release 1.4:

* New macros AC_HAVE_POUNDBANG, AC_TIME_WITH_SYS_TIME, AC_LONG_DOUBLE,
  AC_GETGROUPS_T, AC_DEFINE_UNQUOTED.
* autoconf and autoheader use the M4 environment variable to determine the
  path of the m4 program to use.
* The --macrodir option to autoconf and autoheader specifies the directory
  in which acspecific.m4, acgeneral.m4, etc. reside if not the default.
* autoconf and autoheader can take `-' as their file names, which means to
  read stdin as input.
* Resulting configure scripts can take a --verbose option which causes them
  to print the results of their tests.
* AC_DEFINE quotes its second argument in such a way that spaces, magic
  shell characters, etc. will be preserved during various stages of
  expansion done by the shell.  If you don't want this, use
  AC_DEFINE_UNQUOTED instead.
* Much textual processing done with external calls to tr and sed have been
  internalized with builtin m4 `patsubst' and `translit' calls.
* AC_OUTPUT doesn't hardwire the filenames it outputs.  Instead, you can
  set the shell variables `gen_files' and `gen_config' to the list of
  filenames to output.
* AC_DECLARE_YYTEXT does an AC_SUBST of `LEX_OUTPUT_ROOT', which may be
  "lex.yy" or "lexyy", depending on the system.
* AC_PROGRAMS_CHECK takes an optional third arg.  If given, it is used as
  the default value.
* If AC_ALLOCA chooses alloca.c, it also defines STACK_DIRECTION.
* AC_CONST works much more reliably on more systems.
* Many bug fixes.

Major changes in release 1.3:

configure no longer requires awk for packages that use a config.h.
Support handling --with-PACKAGE options.
New `autoheader' script to create `config.h.in' from `configure.in'.
Ignore troublesome -lucb and -lPW when searching for alloca.
Rename --exec_prefix to --exec-prefix for GNU standards conformance.
Improve detection of STDC library.
Add AC_HAVE_LIBRARY to check for non-default libraries.
Function checking should work with future GNU libc releases.

Major changes in release 1.2:

The --srcdir option is now usually unnecessary.
Add a file containing sample comments describing CPP macros.
A comment in config.status tells which host it was configured on.
Substituted variable values can now contain commas.
Fix bugs in various feature checks.

Major changes in release 1.1:

Added AC_STRCOLL macro.
Made AC_GETLOADAVG check for more things.
AC_OUTPUT argument is now optional.
Various bug fixes.