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Improve AC_DEFUN_ONCE semantics.
* lib/m4sugar/m4sugar.m4 (m4_defun_once): Rewrite to be no-op, rather than warning, on second use, and make sure first use never occurs out of order. * tests/m4sugar.at (m4@&t@_require: one-shot initialization): Enhance test. * tests/base.at (AC_REQUIRE & AC_DEFUN_ONCE: [Require, expand], (AC_REQUIRE & AC_DEFUN_ONCE: [Expand, require]): Adjust tests. * NEWS: Document this. * doc/autoconf.texi (Macro Definitions) <AC_DEFUN>: Mention AC_DEFUN_ONCE. (Prerequisite Macros) <AC_REQUIRE>: Likewise. (Expanded Before Required): Likewise. (One-Shot Macros) <AC_DEFUN_ONCE>: Document new semantics. Reported by Bruno Haible, with suggestion by Paolo Bonzini. Signed-off-by: Eric Blake <ebb9@byu.net>
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Eric Blake
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18
ChangeLog
18
ChangeLog
@ -1,3 +1,21 @@
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2009-01-26 Eric Blake <ebb9@byu.net>
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Improve AC_DEFUN_ONCE semantics.
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* lib/m4sugar/m4sugar.m4 (m4_defun_once): Rewrite to be no-op,
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rather than warning, on second use, and make sure first use never
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occurs out of order.
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* tests/m4sugar.at (m4@&t@_require: one-shot initialization):
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Enhance test.
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* tests/base.at (AC_REQUIRE & AC_DEFUN_ONCE: [Require, expand],
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(AC_REQUIRE & AC_DEFUN_ONCE: [Expand, require]): Adjust tests.
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* NEWS: Document this.
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* doc/autoconf.texi (Macro Definitions) <AC_DEFUN>: Mention
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AC_DEFUN_ONCE.
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(Prerequisite Macros) <AC_REQUIRE>: Likewise.
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(Expanded Before Required): Likewise.
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(One-Shot Macros) <AC_DEFUN_ONCE>: Document new semantics.
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Reported by Bruno Haible, with suggestion by Paolo Bonzini.
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2009-01-24 Eric Blake <ebb9@byu.net>
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Fix typos in recent patches.
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6
NEWS
6
NEWS
@ -14,6 +14,12 @@ GNU Autoconf NEWS - User visible changes.
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the bug in earlier autoconf versions and avoid increased script
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size in the current version.
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** AC_DEFUN_ONCE has improved semantics. Previously, a macro declared
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with AC_DEFUN_ONCE warned on a second invocation; and out-of-order
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expansion was still possible. Now, dependencies are guaranteed,
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and subsequent invocations are a silent no-op. This makes
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AC_DEFUN_ONCE an ideal macro for silencing AC_REQUIRE warnings.
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** AC_LANG_ERLANG works once again (regression introduced in 2.61a).
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** AC_HEADER_ASSERT is fixed so that './configure --enable-assert' no
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@ -12830,7 +12830,8 @@ the argument to @code{AC_REQUIRE}. The other category includes macros
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which are shorthand for a fixed block of text, and therefore do not take
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arguments. For this category of macros, directly expanding the macro
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multiple times results in redundant output, so it is more common to use
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the macro as the argument to @code{AC_REQUIRE}.
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the macro as the argument to @code{AC_REQUIRE}, or to declare the macro
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with @code{AC_DEFUN_ONCE} (@pxref{One-Shot Macros}).
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Be sure to properly quote both the @var{macro-body} @emph{and} the
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@var{macro-name} to avoid any problems if the macro happens to have
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@ -13171,7 +13172,9 @@ in C
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The bug is not in Autoconf, but in the macro definitions. If you ever
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pass a particular macro name to @code{AC_REQUIRE}, then you are implying
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that the macro only needs to be expanded once. But to enforce this, all
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that the macro only needs to be expanded once. But to enforce this,
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either the macro must be declared with @code{AC_DEFUN_ONCE} (although
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this only helps in Autoconf 2.64 or newer), or all
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uses of that macro should be through @code{AC_REQUIRE}; directly
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expanding the macro defeats the point of using @code{AC_REQUIRE} to
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eliminate redundant expansion. In the example, this rule of thumb was
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@ -13271,16 +13274,21 @@ macros can be defined using @code{AC_DEFUN_ONCE}.
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@defmac AC_DEFUN_ONCE (@var{macro-name}, @var{macro-body})
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@acindex{DEFUN_ONCE}
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Declare macro @var{macro-name} like @code{AC_DEFUN} would (@pxref{Macro
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Definitions}), and emit a warning any time the macro is called more than
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once.
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Definitions}), but add additional logic that guarantees that only the
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first use of the macro (whether by direct expansion or
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@code{AC_REQUIRE}) causes an expansion of @var{macro-body}; the
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expansion will occur before the start of any enclosing macro defined by
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@code{AC_DEFUN}. Subsequent expansions are silently ignored.
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Generally, it does not make sense for @var{macro-body} to use parameters
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such as @code{$1}.
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@end defmac
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Obviously it is not sensible to evaluate a macro defined by
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@code{AC_DEFUN_ONCE} in a macro defined by @code{AC_DEFUN}.
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Most of the time you want to use @code{AC_REQUIRE} (@pxref{Prerequisite
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Macros}).
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Prior to Autoconf 2.64, a macro defined by @code{AC_DEFUN_ONCE} would
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emit a warning if it was directly expanded a second time, so for
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portability, it is better to use @code{AC_REQUIRE} than direct
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invocation of @var{macro-name} inside a macro defined by @code{AC_DEFUN}
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(@pxref{Prerequisite Macros}).
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@node Obsoleting Macros
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@section Obsoleting Macros
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@ -22867,7 +22875,10 @@ $ @kbd{autoconf}
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@noindent
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To avoid this warning, decide what purpose the macro in question serves.
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If it only needs to be expanded once (for example, if it provides
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initialization text used by later macros), then the fix is to change all
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initialization text used by later macros), then the simplest fix is to
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change the macro to be declared with @code{AC_DEFUN_ONCE}
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(@pxref{One-Shot Macros}), although this only works in Autoconf 2.64 and
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newer. A more portable fix is to change all
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instances of direct calls to instead go through @code{AC_REQUIRE}
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(@pxref{Prerequisite Macros}). If, instead, the macro is parameterized
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by arguments or by the current definition of other macros in the m4
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@ -1914,14 +1914,17 @@ m4_define([m4_defun_init],
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# m4_defun_once(NAME, EXPANSION)
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# ------------------------------
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# Like m4_defun, but issues the EXPANSION only once, and warns if used
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# several times.
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# Like m4_defun, but guarantee that EXPANSION only happens once
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# (thereafter, using NAME is a no-op).
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#
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# If _m4_divert_dump is empty, we are called at the top level;
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# otherwise, we must ensure that we are required in front of the
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# current defun'd macro.
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m4_define([m4_defun_once],
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[m4_define([m4_location($1)], m4_location)dnl
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m4_define([$1],
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[m4_provide_if([$1],
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[m4_warn([syntax], [$1 invoked multiple times])],
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[_m4_defun_pro([$1])$2[]_m4_defun_epi([$1])])])])
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[m4_define([m4_location($1)], m4_location)]dnl
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[m4_define([$1], [m4_pushdef([$1])m4_if(_m4_divert_dump, [],
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[_m4_defun_pro([$1])$2[]_m4_defun_epi([$1])],
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[_m4_require_call([$1], [$2[]m4_provide([$1])], _m4_divert_dump)])])])
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# m4_pattern_forbid(ERE, [WHY])
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@ -2,8 +2,8 @@
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AT_BANNER([Autoconf base layer.])
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# Copyright (C) 2000, 2001, 2003, 2005, 2006, 2007, 2008 Free Software
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# Foundation, Inc.
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# Copyright (C) 2000, 2001, 2003, 2005, 2006, 2007, 2008, 2009 Free
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# Software Foundation, Inc.
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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@ -28,6 +28,7 @@ AT_BANNER([Autoconf base layer.])
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# Check that dependencies are always properly honored.
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AT_SETUP([AC_REQUIRE: topological sort])
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AT_KEYWORDS([m4@&t@_require])
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AT_DATA([configure.ac],
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[[define([REQUIRE_AND_CHECK],
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@ -71,6 +72,7 @@ AT_CLEANUP
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# Check that the message mentions AC_DEFUN, not m4_defun.
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AT_SETUP([AC_REQUIRE: error message])
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AT_KEYWORDS([m4@&t@_require])
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AT_DATA([configure.ac],
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[[AC_REQUIRE([AC_PROG_CC])
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]])
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@ -88,6 +90,7 @@ AT_CLEANUP
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## ----------------------------------------------- ##
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AT_SETUP([AC_REQUIRE & AC_DEFUN_ONCE: [Require, expand]])
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AT_KEYWORDS([m4@&t@_require m4@&t@_require_once])
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AT_DATA([configure.ac],
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[[AC_DEFUN([TEST],
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@ -116,10 +119,7 @@ case $multi_test:$single_test in
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esac
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]])
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AT_CHECK_AUTOCONF([], 0, [],
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[configure.ac:17: warning: SINGLE_TEST invoked multiple times
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configure.ac:18: warning: SINGLE_TEST invoked multiple times
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])
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AT_CHECK_AUTOCONF([], 0, [])
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AT_CHECK_CONFIGURE
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@ -132,6 +132,7 @@ AT_CLEANUP
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## ----------------------------------------------- ##
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AT_SETUP([AC_REQUIRE & AC_DEFUN_ONCE: [Expand, require]])
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AT_KEYWORDS([m4@&t@_require m4@&t@_require_once])
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AT_DATA([configure.ac],
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[[AC_DEFUN([TEST],
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@ -161,9 +162,7 @@ case $multi_test:$single_test in
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esac
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]])
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AT_CHECK_AUTOCONF([], 0, [],
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[configure.ac:16: warning: SINGLE_TEST invoked multiple times
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])
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AT_CHECK_AUTOCONF([], 0, [])
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AT_CHECK_CONFIGURE
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AT_CLEANUP
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@ -175,6 +174,7 @@ AT_CLEANUP
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## ------------------------- ##
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AT_SETUP([AC_REQUIRE & AC_PROVIDE])
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AT_KEYWORDS([m4@&t@_require])
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AT_DATA([configure.ac],
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[[AC_DEFUN([TEST],
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@ -430,8 +430,9 @@ AT_CLEANUP
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AT_SETUP([m4@&t@_require: one-shot initialization])
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AT_KEYWORDS([m4@&t@_require])
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AT_KEYWORDS([m4@&t@_defun_init m4@&t@_copy])
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AT_KEYWORDS([m4@&t@_defun_init m4@&t@_copy m4@&t@_defun_once])
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dnl check out m4_defun_init, m4_copy, and odd macro names
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AT_CHECK_M4SUGAR_TEXT([[
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m4_defun_init([a], [[init a
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]], [[common a]])dnl
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@ -455,6 +456,33 @@ hello, world
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goodbye
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hello, again
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]])
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dnl Check m4_defun_once behavior
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AT_CHECK_M4SUGAR_TEXT([[
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m4_defun_once([a], [[a]])dnl
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m4_defun([b], [[b]m4_require([a])])dnl
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m4_defun([c], [[c]
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a[]m4_require([b])])dnl
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c
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a
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m4_defun_once([d], [[d]m4_require([a])])dnl
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d
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m4_defun_once([e], [[e]])dnl
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m4_defun([f], [[f]m4_require([e])e])dnl
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f
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]], [[
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a
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b
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c
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d
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e
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f
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]])
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AT_CLEANUP
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