Re: Avoid O(n^2) recursion in m4sugar

[Eric Blake]

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According to Eric Blake on 7/25/2008 5:56 PM:
| The patch
| makes a runtime decision during m4_init on which version to use, so that
| m4 1.6 users automatically benefit from the faster of two available linear
| methods, while m4 1.4.x users get the only linear method.

| @@ -2293,6 +2311,13 @@ m4_define([m4_init],
|  m4_pattern_forbid([^_?m4_])
|  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; nothing further
| +# needs to be done.  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.
| +m4_ifndef([__m4_version__], [m4_include([m4sugar/foreach.m4])])
| +

This portion of the patch caused an infinite loop in aclocal - aclocal
recognized that the creation of aclocal.m4 now has an optional dependency
on an m4_include'd file, and triggered another round of autoreconf to try
to pick it up.  Fixed as follows, by hiding the file from aclocal via
m4_builtin.

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

Eric Blake             address@hidden
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>From e48d698fdc54635576c491b1ed2c66fa289d80f9 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Fri, 25 Jul 2008 21:13:23 -0600
Subject: [PATCH] Avoid infinite aclocal loop.

* lib/m4sugar/m4sugar.m4 (m4_init): Bypass m4_include tracing, so
that aclocal doesn't insist on finding m4sugar/foreach.m4.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog              |    4 ++++
 lib/m4sugar/m4sugar.m4 |    5 +++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 1cc7cd6..c2147d9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2008-07-25  Eric Blake  <address@hidden>
 
+       Avoid infinite aclocal loop.
+       * lib/m4sugar/m4sugar.m4 (m4_init): Bypass m4_include tracing, so
+       that aclocal doesn't insist on finding m4sugar/foreach.m4.
+
        Provide O(n) replacement macros for M4 1.4.x.
        * lib/m4sugar/foreach.m4: New file.
        (m4_foreach, m4_case, _m4_shiftn, m4_do, m4_dquote_elt, _m4_map)
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index 1480953..3e201b9 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -2315,8 +2315,9 @@ m4_pattern_forbid([^dnl$])
 # 1.6 or newer, and thus that $@ recursion is linear; nothing further
 # needs to be done.  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.
-m4_ifndef([__m4_version__], [m4_include([m4sugar/foreach.m4])])
+# foreach-based replacement macros.  Use the raw builtin to avoid
+# tripping up include tracing.
+m4_ifndef([__m4_version__], [m4_builtin([include], [m4sugar/foreach.m4])])
 
 # _m4_divert_diversion should be defined:
 m4_divert_push([KILL])
-- 
1.5.6.4