2006-06-02  Stepan Kasal  <address@hidden>

	* lib/m4sugar/m4sh.m4 (_AS_HERE_DOC_WORKS): Check for the
	ksh93f bug with long here-documents.
	(AS_INIT): Require this check.
	* doc/autoconf.texi (Here-Documents): Add more details about
	the bug.

Index: lib/m4sugar/m4sh.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/m4sugar/m4sh.m4,v
retrieving revision 1.190
diff -u -r1.190 m4sh.m4
--- lib/m4sugar/m4sh.m4	31 May 2006 09:44:39 -0000	1.190
+++ lib/m4sugar/m4sh.m4	2 Jun 2006 11:37:00 -0000
@@ -1459,6 +1459,31 @@
 }
 ])
 
+# _AS_HERE_DOC_WORKS
+# ------------------
+# ksh versions prior to ksh93g mishandle braced variable expansion in
+# non-quoted here-documents, if the variable name crosses a block boundary
+# (block can be 1024 or 4096 bytes).  Check for this.
+#
+m4_define([_AS_HERE_DOC_WORKS], [
+# (2^6 - 1) dots
+as_d=...............................................................
+# (2^9 - 1) characters
+as_d="$as_d:$as_d:$as_d:$as_d
+$as_d:$as_d:$as_d:$as_d"
+$as_shell >/dev/null 2>&1 <<_ASOUTER
+foobar=OK
+bar=BAD
+# the first two lines expand to (2^12 - 6) characters (including the two
+# trailing newlines), so the 4096 boundary appears between "{foo" and "bar}"
+grep OK <<_ASINNER
+$as_d$as_d$as_d$as_d
+$as_d$as_d$as_d$as_d
+ \${foobar}
+_ASINNER
+_ASOUTER
+])
+
 
 # AS_INIT
 # -------
@@ -1473,6 +1498,7 @@
 m4_divert_text([BINSH], address@hidden:@! /bin/sh])
 m4_divert_text([M4SH-SANITIZE], [AS_SHELL_SANITIZE])
 AS_REQUIRE([_AS_SHELL_FN_SPY])
+_AS_DETECT_REQUIRED([_AS_HERE_DOC_WORKS])
 
 # Let's go!
 m4_wrap([m4_divert_pop([BODY])[]])
Index: doc/autoconf.texi
===================================================================
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.1033
diff -u -r1.1033 autoconf.texi
--- doc/autoconf.texi	1 Jun 2006 07:47:40 -0000	1.1033
+++ doc/autoconf.texi	2 Jun 2006 12:28:40 -0000
@@ -10792,11 +10792,14 @@
 inefficiently.  And some shells mishandle large here-documents: for example,
 Solaris 10 @command{dtksh} and the UnixWare 7.1.1 Posix shell, which are
 derived from Korn shell version M-12/28/93d, mishandle braced variable
-expansion @address@hidden@}} that crosses a 1024- or 4096-byte buffer boundary
-within a here-document.  If the closing brace does not lie on the boundary,
-the failure is silent and the variable expansion will be empty, otherwise
-the shell will report a bad substitution.  This bug can usually be worked
-around by omitting the braces: @code{$var}.  The bug was fixed in
+expansion that crosses a 1024- or 4096-byte buffer boundary
+within a here-document.  Only the part of the variable name after the boundary
+is used.  For example, @address@hidden@}} could be replaced by the expansion
+of @address@hidden@}}.  If the end of the variable name is aligned with the block
+boundary, the shell reports an error, as if you used @address@hidden@}}.
+Instead of @address@hidden@}}, the shell may expand
address@hidden@address@hidden, or even @address@hidden@}}.  This bug can usually
+be worked around by omitting the braces: @code{$var}.  The bug was fixed in
 @samp{ksh93g} (1998-04-30) but as of 2006 many operating systems were
 still shipping older versions with the bug.