[CCing autoconf-patches]
Paul Eggert wrote in
<https://lists.gnu.org/archive/html/bug-gnulib/2020-10/msg00019.html>:
> > AFAICS, this is relevant for code written directly into configure.ac. But
> > inside an AC_DEFUN it is irrelevant, because required macros are hoisted
> > before the body of the AC_DEFUN anyway.
>
> I was playing it safe based on this NEWS item from Autoconf 2.69c:
>
> - Autoconf macros that use AC_REQUIRE internally, are not safe to
> use inside of hand-written shell control-flow constructs. Use
> AS_IF, AS_CASE, AS_FOR, etc. instead. (See the “Prerequisite
> Macros” section of the manual for further explanation.)
>
> Since I didn't know whether the macros in question used AC_REQUIRE
> internally, I
> played it safe.
>
> But now that you mention it, AS_IF isn't needed here and I installed the
> attached further patch. Also, to help prevent others from making a similar
> mistake, I plan to reword the Autoconf NEWS item to start with something like
> "Autoconf macros that use AC_REQUIRE are not safe to use in hand-written
> shell
> control-flow constructs that appear outside of macros defined by AC_DEFUN."
Thanks. But if you, Paul, make an incorrect assumption about what AS_IF really
does, how many more users (who read only the documentation) will make the same
mistake? I therefore think the documentation should be enhanced to avoid this
misinterpretation.
Proposed patch attached.
Bruno
From 11b827d202aa07b2b8c8f894d8f49844d570dfe9 Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Tue, 6 Oct 2020 23:46:42 +0200
Subject: [PATCH] Clarify that AS_IF and AS_CASE are overkill inside AC_DEFUN.
* doc/autoconf.texi (Common Shell Constructs): Document that AS_IF and AS_CASE
provide no benefit regarding required macros when used inside macros defined
by AC_DEFUN or AC_DEFUN_ONCE.
* NEWS: Don't mention the undocumented macro AS_FOR.
---
NEWS | 4 ++--
doc/autoconf.texi | 16 +++++++++++++++-
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/NEWS b/NEWS
index 55e938b..5335709 100644
--- a/NEWS
+++ b/NEWS
@@ -36,8 +36,8 @@ GNU Autoconf NEWS - User visible changes.
- Autoconf macros that use AC_REQUIRE internally, are not safe to
use inside of hand-written shell control-flow constructs. Use
- AS_IF, AS_CASE, AS_FOR, etc. instead. (See the “Prerequisite
- Macros” section of the manual for further explanation.)
+ AS_IF, AS_CASE, etc. instead. (See the “Prerequisite Macros”
+ section of the manual for further explanation.)
The set of macros that use AC_REQUIRE internally may change from
release to release. The only macros that are guaranteed *not* to
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index dea85e4..f8d8f8b 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -13759,7 +13759,15 @@ Expand into a shell @samp{case} statement, where @var{word} is matched
against one or more patterns. @var{if-matched} is run if the
corresponding pattern matched @var{word}, else @var{default} is run.
Avoids several portability issues (@pxref{case, , Limitations of Shell
-Builtins}).
+Builtins}). Also, @code{AS_CASE} ensures any macros required by
+@var{if-matched1}, @dots{}, @var{default} are expanded before the
+@samp{case} statement.
+
+The handling of required macros provided by @code{AS_CASE} is useful
+in @file{configure.ac}, outside of macros defined by @code{AC_DEFUN}
+or @code{AC_DEFUN_ONCE}. Inside macros defined by @code{AC_DEFUN}
+or @code{AC_DEFUN_ONCE}, @code{AS_CASE} and the plain shell @samp{case}
+syntax are equivalent.
@end defmac
@c Deprecated, to be replaced by a better API
@@ -13881,6 +13889,12 @@ blanks, or expand to a nonempty shell command. For example,
argument contains the nonblank characters @code{[]} which expand to
nothing. This restriction on @var{run-if-false} also applies to other
macros with ``if-false'' arguments denoting shell commands.
+
+The handling of required macros provided by @code{AS_IF} is useful
+in @file{configure.ac}, outside of macros defined by @code{AC_DEFUN}
+or @code{AC_DEFUN_ONCE}. Inside macros defined by @code{AC_DEFUN}
+or @code{AC_DEFUN_ONCE}, @code{AS_IF} and the plain shell @samp{if}
+syntax are equivalent.
@end defmac
@defmac AS_MKDIR_P (@var{file-name})
--
2.7.4
