Re: git autoconf build is failing tests

[Eric Blake]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

According to Eric Blake on 11/10/2008 7:53 PM:
> I downgraded, and I can reproduce a different crash on cygwin, so it looks
> like we're now tickling a m4 memory corruption bug:
> 
> Meanwhile, m4 1.4.11 passed.  I'm in the middle of bisecting which
> autoconf patch tickled the bug, and which m4 release fixed it.

Found it.  The NEWS for m4 1.4.9b states:

* The `format' builtin now understands formats such as %a, %A, and %'hhd,
  and works around a number of platform printf bugs.  Furthermore, the
  sequence format(%*.*d,-1,-1,1) no longer outputs random data.

And sure enough:

$ m4-1.4.9/src/m4
format("%.1s",abc)
"a"
format("%.*s",-1,abc)
"(L""
format("%.*s",-2,abc)
"abc"
format("%.*s",1,abc)
"a"

$ ../m4-1.4.9b/src/m4
format("%.1s",abc)
"a"
format("%.*s",-1,abc)
"abc"
format("%.*s",-2,abc)
"abc"
format("%.*s",1,abc)
"a"

I'm not yet ready to require m4 1.4.10 (1.4.5 is still not even 3 years
old), so the correct solution is to avoid tickling the bug.  Since the bug
is only present when using exactly -1 as a precision argument; any other
value works.  Meanwhile, I didn't want to penalize newer m4 with the extra
m4_eval, hence I created a new m4sugar macro _m4_index, and make it
directly use the builtin on newer m4.  I'm committing this, tested across
a number of versions spanning from m4 1.4.5 through m4.git.  It also fixes
an accidental regression in the final hunk of
http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=2922868#patch7,


- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAkkZBNUACgkQ84KuGfSFAYBIIwCdGHk7R1kEStxZxhw454BoPMBL
svIAnRt6jOOJPLSNir0mGiBVKloFWJhJ
=y3iB
-----END PGP SIGNATURE-----

>From 74bb1a450dd690f08cd39a6597f2acbb76c69024 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Mon, 10 Nov 2008 21:00:44 -0700
Subject: [PATCH] Work around <=m4-1.4.9 bug in m4_format.

* lib/m4sugar/m4sugar.m4 (_m4_index): New internal macro.
(m4_init): Only use it in older m4.
* lib/autoconf/general.m4 (_AC_DEFINE_Q): Use it to avoid
m4_format bug in older m4.
* lib/autoconf/status.m4 (_AC_CONFIG_COMPUTE_DEST): Likewise.
Reported by Bob Proulx.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog               |   10 ++++++++++
 lib/autoconf/general.m4 |    4 +++-
 lib/autoconf/status.m4  |    4 ++--
 lib/m4sugar/m4sugar.m4  |   26 ++++++++++++++++++++++----
 4 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2367c7c..b28abcd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2008-11-10  Eric Blake  <address@hidden>
 
+       Work around <=m4-1.4.9 bug in m4_format.
+       * lib/m4sugar/m4sugar.m4 (_m4_index): New internal macro.
+       (m4_init): Only use it in older m4.
+       * lib/autoconf/general.m4 (_AC_DEFINE_Q): Use it to avoid
+       m4_format bug in older m4.
+       * lib/autoconf/status.m4 (_AC_CONFIG_COMPUTE_DEST): Likewise.
+       Reported by Bob Proulx.
+
+2008-11-10  Eric Blake  <address@hidden>
+
        Match upstream standards.texi.
        * doc/standards.texi: Resync from upstream.
        * doc/fdl-1.3.texi: Rename...
diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 2c184fc..15377cb 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -2077,8 +2077,10 @@ m4_define([AC_DEFINE_UNQUOTED], [_AC_DEFINE_Q([], $@)])
 # m4_format rather than regex to grab prefix up to first ().  AC_name
 # is defined with over-quotation, so that we can avoid m4_defn; this
 # is only safe because the name should not contain $.
+#
+# Use _m4_index to avoid a bug in m4_format in older m4.
 m4_define([_AC_DEFINE_Q],
-[m4_pushdef([AC_name], m4_format([[[%.*s]]], m4_index([$2], [(]), [$2]))]dnl
+[m4_pushdef([AC_name], m4_format([[[%.*s]]], _m4_index([$2], [(]), [$2]))]dnl
 [AC_DEFINE_TRACE(AC_name)]dnl
 [m4_cond([m4_index([$3], [
 ])], [-1], [],
diff --git a/lib/autoconf/status.m4 b/lib/autoconf/status.m4
index 388b90f..c134bb7 100644
--- a/lib/autoconf/status.m4
+++ b/lib/autoconf/status.m4
@@ -247,9 +247,9 @@ m4_define([_AC_CONFIG_FOOS],
 # _AC_CONFIG_COMPUTE_DEST(STRING)
 # -------------------------------
 # Compute the DEST from STRING by stripping any : and following
-# characters.
+# characters.  Use _m4_index to avoid a bug in m4_format in older m4.
 m4_define([_AC_CONFIG_COMPUTE_DEST],
-[m4_format([[%.*s]], m4_index([$1], [:]), [$1])])
+[m4_format([[%.*s]], _m4_index([$1], [:]), [$1])])
 
 # _AC_CONFIG_REGISTER(MODE, TAG, [COMMANDS])
 # ------------------------------------------
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index 2a0d7ce..8884714 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -625,6 +625,22 @@ m4_define([m4_dumpdefs],
        [m4_map_args([$0], $@)])])
 
 
+# _m4_index(HAYSTACK, NEEDLE)
+# ---------------------------
+# Like the original, except return -2 instead of -1 if NEEDLE is not
+# present in HAYSTACK.  That way, it can be used to work around a bug
+# in m4 1.4.9 and earlier where m4_format did not accept a precision
+# of -1; this macro can be safely used in the idiom:
+#   m4_format([[%.*s]], _m4_index([$1],[$2]), [$1])
+# to grab the prefix of $1 up to but excluding $2, if it was present,
+# otherwise the entire $1.
+m4_define([_m4_index],
+[$0_(m4_index($@))])
+
+m4_define([_m4_index_],
+[m4_if([$1], [-1], [-2], [$1])])
+
+
 # m4_popdef(NAME)
 # ---------------
 # Like the original, except guarantee a warning when using something which is
@@ -2975,7 +2991,8 @@ m4_pattern_forbid([^dnl$])
 
 # If __m4_version__ is defined, we assume that we are being run by M4
 # 1.6 or newer, and thus that $@ recursion is linear and debugmode(d)
-# is available for faster checks of dereferencing undefined macros.
+# is available for faster checks of dereferencing undefined macros,
+# and we don't need to worry about _m4_format bugs with _m4_index.
 # But if it is missing, we assume we are being run by M4 1.4.x, that
 # $@ recursion is quadratic, and that we need foreach-based
 # replacement macros.  Use the raw builtin to avoid tripping up
@@ -2983,9 +3000,10 @@ m4_pattern_forbid([^dnl$])
 # undefines m4_defn.
 m4_ifdef([__m4_version__],
 [m4_debugmode([+d])
-m4_define([m4_defn], _m4_defn([m4_defn]))
-m4_define([m4_popdef], _m4_defn([m4_popdef]))
-m4_define([m4_undefine], _m4_defn([m4_undefine]))],
+m4_define([m4_defn], _m4_defn([_m4_defn]))
+m4_define([_m4_index], _m4_defn([m4_index]))
+m4_define([m4_popdef], _m4_defn([_m4_popdef]))
+m4_define([m4_undefine], _m4_defn([_m4_undefine]))],
 [m4_builtin([include], [m4sugar/foreach.m4])])
 
 # Rewrite the first entry of the diversion stack.
-- 
1.6.0.2