minor improvements for {...} problem; also, prefer && to ;

[Paul Eggert]

I installed this:

2007-11-09  Paul Eggert  <address@hidden>

        * doc/autoconf.texi (Limitations of Builtins): Document problem
        with { ... } a bit more clearly.  Suggest ":;{" as a shorthand
        for the workaround.
        * lib/m4sugar/Makefile.am (version.m4): Detect 'echo' failure.
        Use ":;{" shorthand.
        * tests/Makefile.am ($(srcdir)/package.m4): Likewise.

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 421056e..1dcd60b 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -13564,11 +13564,10 @@ if @var{command}; then (exit 1); else :; fi
 @item @address@hidden@}}
 @c --------------------
 @prindex @address@hidden@}}
-As recently as GNU Bash 3.2, some shells do not properly set @samp{$?}
-when failing to write redirected output of any compound command other
-than a subshell group, when that compound command is the first thing
-executed.  This is most commonly observed with @address@hidden, but also 
affects
-other compound commands.
+Bash 3.2 and earlier sometimes does not properly set @samp{$?} when
+failing to write redirected output of a compound command.  This problem
+is most commonly observed with @address@hidden@address@hidden; it does not 
occur
+with @samp{(@dots{})}.  For example:

 @example
 $ @kbd{bash -c '@{ echo foo; @} >/bad; echo $?'}
@@ -13579,14 +13578,10 @@ bash: line 1: /bad: Permission denied
 0
 @end example

-The workaround is simple: prime bash with a simple command before any
-compound command with redirection.
+To work around the bug, prepend @samp{:;}:

 @example
-$ @kbd{bash -c ':; @{ echo foo; @} >/bad; echo $?'}
-bash: line 1: /bad: Permission denied
-1
-$ @kbd{bash -c ':; while :; do echo; done >/bad; echo $?'}
+$ @kbd{bash -c ':;@{ echo foo; @} >/bad; echo $?'}
 bash: line 1: /bad: Permission denied
 1
 @end example
diff --git a/lib/m4sugar/Makefile.am b/lib/m4sugar/Makefile.am
index de32907..7360ca1 100644
--- a/lib/m4sugar/Makefile.am
+++ b/lib/m4sugar/Makefile.am
@@ -26,17 +26,16 @@ CLEANFILES = $(nodist_m4sugarlib_DATA)

 # The `:;' works around a redirected compound command bash exit status bug.
 version.m4: $(top_srcdir)/configure.ac
-       :; \
-       {                                       \
-         echo '# This file is part of -*- Autoconf -*-.'; \
-         echo '# Version of Autoconf.'; \
-         echo '# Copyright (C) 1999, 2000, 2001, 2002, 2006, 2007'; \
-         echo '# Free Software Foundation, Inc.'; \
-         echo ;\
-         echo 'm4_define([m4_PACKAGE_NAME],      [$(PACKAGE_NAME)])'; \
-         echo 'm4_define([m4_PACKAGE_TARNAME],   [$(PACKAGE_TARNAME)])'; \
-         echo 'm4_define([m4_PACKAGE_VERSION],   [$(PACKAGE_VERSION)])'; \
-         echo 'm4_define([m4_PACKAGE_STRING],    [$(PACKAGE_STRING)])'; \
+       :;{ \
+         echo '# This file is part of -*- Autoconf -*-.' && \
+         echo '# Version of Autoconf.' && \
+         echo '# Copyright (C) 1999, 2000, 2001, 2002, 2006, 2007' && \
+         echo '# Free Software Foundation, Inc.' && \
+         echo  &&\
+         echo 'm4_define([m4_PACKAGE_NAME],      [$(PACKAGE_NAME)])' && \
+         echo 'm4_define([m4_PACKAGE_TARNAME],   [$(PACKAGE_TARNAME)])' && \
+         echo 'm4_define([m4_PACKAGE_VERSION],   [$(PACKAGE_VERSION)])' && \
+         echo 'm4_define([m4_PACKAGE_STRING],    [$(PACKAGE_STRING)])' && \
          echo 'm4_define([m4_PACKAGE_BUGREPORT], [$(PACKAGE_BUGREPORT)])'; \
        } >version.m4

diff --git a/tests/Makefile.am b/tests/Makefile.am
index ed129fd..45267ff 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -34,15 +34,14 @@ include ../lib/freeze.mk
 ## package.m4.  ##
 ## ------------ ##

-# The `:;' works around a redirected compound command bash exit status bug.
+# The `:;' works around a Bash 3.2 bug when the output is not writeable.
 $(srcdir)/package.m4: Makefile
-       :; \
-       {                                       \
-         echo '# Signature of the current package.'; \
-         echo 'm4_define([AT_PACKAGE_NAME],      [$(PACKAGE_NAME)])'; \
-         echo 'm4_define([AT_PACKAGE_TARNAME],   [$(PACKAGE_TARNAME)])'; \
-         echo 'm4_define([AT_PACKAGE_VERSION],   [$(PACKAGE_VERSION)])'; \
-         echo 'm4_define([AT_PACKAGE_STRING],    [$(PACKAGE_STRING)])'; \
+       :;{ \
+         echo '# Signature of the current package.' && \
+         echo 'm4_define([AT_PACKAGE_NAME],      [$(PACKAGE_NAME)])' && \
+         echo 'm4_define([AT_PACKAGE_TARNAME],   [$(PACKAGE_TARNAME)])' && \
+         echo 'm4_define([AT_PACKAGE_VERSION],   [$(PACKAGE_VERSION)])' && \
+         echo 'm4_define([AT_PACKAGE_STRING],    [$(PACKAGE_STRING)])' && \
          echo 'm4_define([AT_PACKAGE_BUGREPORT], [$(PACKAGE_BUGREPORT)])'; \
        } >$(srcdir)/package.m4