From: Eric Blake <eblake@redhat.com>
Date: Wed, 25 Aug 2010 22:56:37 +0000 (-0600)
Subject: m4sh: assume ${a:-b} support
X-Git-Tag: v2.68~43
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d1bea5123b8ecb406fbeabbe70552271f60de8e7;p=thirdparty%2Fautoconf.git

m4sh: assume ${a:-b} support

* tests/m4sh.at (Null variable substitution): New test.
* doc/autoconf.texi (Shell Substitutions) <${var:-value}>: Mention
that m4sh guarantees support.
(Limitations of Usual Tools) <mktemp>: Use it.
* lib/m4sugar/m4sh.m4 (AS_LINENO_POP, AS_VAR_IF, AS_TMPDIR):
Exploit use of colon for smaller files.

Signed-off-by: Eric Blake <eblake@redhat.com>
---

diff --git a/ChangeLog b/ChangeLog
index 92132b32..236bfcdd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2010-08-27  Eric Blake  <eblake@redhat.com>
+
+	m4sh: assume ${a:-b} support
+	* tests/m4sh.at (Null variable substitution): New test.
+	* doc/autoconf.texi (Shell Substitutions) <${var:-value}>: Mention
+	that m4sh guarantees support.
+	(Limitations of Usual Tools) <mktemp>: Use it.
+	* lib/m4sugar/m4sh.m4 (AS_LINENO_POP, AS_VAR_IF, AS_TMPDIR):
+	Exploit use of colon for smaller files.
+
 2010-08-26  Eric Blake  <eblake@redhat.com>
 
 	docs: document m4_define_default
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 996525ac..95500bec 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -15425,6 +15425,9 @@ bad substitution
 Old BSD shells, including the Ultrix @code{sh}, don't accept the
 colon for any shell substitution, and complain and die.
 Similarly for $@{@var{var}:=@var{value}@}, $@{@var{var}:?@var{value}@}, etc.
+However, all shells that support functions allow the use of colon in
+shell substitution, and since m4sh requires functions, you can portably
+use null variable substitution patterns in configure scripts.
 
 @item $@{@var{var}+@var{value}@}
 @cindex $@{@var{var}+@var{value}@}
@@ -18425,7 +18428,7 @@ Here is sample code to create a new temporary directory safely:
 # Create a temporary directory $tmp in $TMPDIR (default /tmp).
 # Use mktemp if possible; otherwise fall back on mkdir,
 # with $RANDOM to make collisions less likely.
-: "$@{TMPDIR=/tmp@}"
+: "$@{TMPDIR:=/tmp@}"
 @{
   tmp=`
     (umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 2f8baec1..8343b259 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -859,8 +859,10 @@ m4_defun([AS_LINENO_PUSH],
 # -----------------------
 # If this is call balances the outermost call to AS_LINENO_PUSH,
 # AS_MESSAGE will restart printing $LINENO as the line number.
+#
+# No need to use AS_UNSET, since as_lineno is necessarily set.
 m4_defun([AS_LINENO_POP],
-[eval $as_lineno_stack; test "x$as_lineno_stack" = x && AS_UNSET([as_lineno])])
+[eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno])
 
 
 
@@ -1620,7 +1622,7 @@ m4_define([_AS_LITERAL_HEREDOC_IF_NO], [$2])
 # it is a documented part of the public API and must not be changed.
 m4_define([AS_TMPDIR],
 [# Create a (secure) tmp directory for tmp files.
-m4_if([$2], [], [: "${TMPDIR=/tmp}"])
+m4_if([$2], [], [: "${TMPDIR:=/tmp}"])
 {
   tmp=`(umask 077 && mktemp -d "m4_default([$2],
     [$TMPDIR])/$1XXXXXX") 2>/dev/null` &&
@@ -1984,10 +1986,12 @@ m4_define([AS_VAR_GET],
 # Polymorphic, and avoids sh expansion error upon interrupt or term signal.
 m4_define([AS_VAR_IF],
 [AS_LITERAL_WORD_IF([$1],
-  [AS_IF([test "x$$1" = x""$2]],
+  [AS_IF(m4_ifval([$2], [[test "x$$1" = x[]$2]], [[${$1:+false} :]])],
   [AS_VAR_COPY([as_val], [$1])
-   AS_IF([test "x$as_val" = x""$2]],
-  [AS_IF([eval test \"x\$"$1"\" = x"_AS_ESCAPE([$2], [`], [\"$])"]]),
+   AS_IF(m4_ifval([$2], [[test "x$as_val" = x[]$2]], [[${as_val:+false} :]])],
+  [AS_IF(m4_ifval([$2],
+    [[eval test \"x\$"$1"\" = x"_AS_ESCAPE([$2], [`], [\"$])"]],
+    [[eval \${$1:+false} :]])]),
 [$3], [$4])])
 
 
diff --git a/tests/m4sh.at b/tests/m4sh.at
index de2bdc96..e73c971f 100644
--- a/tests/m4sh.at
+++ b/tests/m4sh.at
@@ -552,7 +552,71 @@ AT_CHECK([$CONFIG_SHELL ./script])
 
 AT_CLEANUP
 
+## ---------------------------- ##
+## Null variable substitution.  ##
+## ---------------------------- ##
 
+# According to http://www.in-ulm.de/~mascheck/bourne/, all shells with
+# functions also support `${a:-b}'.
+
+AT_SETUP([Null variable substitution])
+AT_KEYWORDS([m4sh])
+
+AT_DATA_M4SH([script.as],
+[[AS_INIT
+
+AS_UNSET([a])
+b=
+c=.
+case ${a:-x}${b:-y}${c:-z} in
+  xy.) ;;
+  *) exit 1 ;;
+esac
+case ${a-x}${b-y}${c-z} in
+  x.) ;;
+  *) exit 2 ;;
+esac
+
+case ${a+x}${b+y}${c+z} in
+  yz) ;;
+  *) exit 3 ;;
+esac
+case ${a:+x}${b:+y}${c:+z} in
+  z) ;;
+  *) exit 4 ;;
+esac
+
+case ${a=x}${b=y}${c=z} in
+  x.) ;;
+  *) exit 5 ;;
+esac
+AS_UNSET([a])
+case ${a:=x}${b:=y}${c:=z} in
+  xy.) ;;
+  *) exit 6 ;;
+esac
+case $a$b$c in
+  xy.) ;;
+  *) exit 7 ;;
+esac
+AS_UNSET([a])
+b=
+
+(: ${a?oops}; echo fail) 2>err && exit 8
+grep oops err >/dev/null || exit 9
+test "${b?oops}" = '' || exit 10
+test "${c?oops}" = . || exit 11
+(: ${a:?oops}; echo fail) 2>err && exit 12
+grep oops err >/dev/null || exit 13
+(: ${b:?oops}; echo fail) 2>err && exit 14
+grep oops err >/dev/null || exit 15
+test "${c:?oops}" = . || exit 16
+]])
+
+AT_CHECK_M4SH
+AT_CHECK([$CONFIG_SHELL ./script])
+
+AT_CLEANUP
 
 
 ## ------------------- ##