better low-level diversion debugging

[Eric Blake]

In order to fix the bug in AC_REQUIRE, I had to track what was happening in low-
level diversion handling.  Tracing m4_builtin was too heavy-handed (we also use 
m4_builtin to implement m4_split, which has unbalanced ] and thus crashes the 
autom4te tracing engine), but tracing m4_divert was too high-level (m4_expand 
makes some of the diversion magic happen on a deferred basis).  So I am 
installing this instead, so that I can trace _m4_divert_raw/_m4_undivert to see 
what is actually happening.  By the way, using _m4_divert_raw is slightly 
faster than m4_builtin([divert]), as it results in fewer hashtable lookups in 
m4.  While I was at it, I found a way to speed up _m4_require_call, which in 
turn exposed a recently added typo in autotest.


From: Eric Blake <address@hidden>
Date: Tue, 30 Dec 2008 08:32:08 -0700
Subject: [PATCH] Make it easier to track diversion bugs.

* lib/m4sugar/m4sugar.m4 (_m4_divert_raw, _m4_undivert): New
internal macros, which are easier to trace than m4_builtin.
(m4_cleardivert, m4_divert, m4_divert_push, m4_divert_pop)
(m4_undivert): Use them.
(_m4_require_call): Likewise.  Use fewer macros.
* lib/autotest/general.m4 (_AT_DECIDE_TRACEABLE): Fix typo.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog               |   10 ++++++++++
 lib/autotest/general.m4 |    2 +-
 lib/m4sugar/m4sugar.m4  |   46 +++++++++++++++++++++++++++-------------------
 3 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index fe0fb5c..d1a5382 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2008-12-30  Eric Blake  <address@hidden>
+
+       Make it easier to track diversion bugs.
+       * lib/m4sugar/m4sugar.m4 (_m4_divert_raw, _m4_undivert): New
+       internal macros, which are easier to trace than m4_builtin.
+       (m4_cleardivert, m4_divert, m4_divert_push, m4_divert_pop)
+       (m4_undivert): Use them.
+       (_m4_require_call): Likewise.  Use fewer macros.
+       * lib/autotest/general.m4 (_AT_DECIDE_TRACEABLE): Fix typo.
+
 2008-12-26  Bruno Haible  <address@hidden>
 
        Improve multiarch detection.
diff --git a/lib/autotest/general.m4 b/lib/autotest/general.m4
index a1079c8..5f2db79 100644
--- a/lib/autotest/general.m4
+++ b/lib/autotest/general.m4
@@ -1988,7 +1988,7 @@ at_fn_check_prepare_notrace],
 dnl We know at build time that tracing COMMANDS is always safe.
 [[at_fn_check_prepare_trace],]dnl
 dnl COMMANDS may contain parameter expansions; expand them at runtime.
-[[at_fn_check_prepare_dynamic "AS_ESCAPE([$1], [`\"])"])])]dnl
+[[at_fn_check_prepare_dynamic "AS_ESCAPE([$1], [`\"])"])[]]dnl
 [_m4_popdef([at_reason])])
 
 
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index f64ef16..556969f 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -134,7 +134,6 @@ m4_ifdef([changeword],dnl conditionally available in 1.4.x
 m4_rename_m4([debugfile])
 m4_rename_m4([debugmode])
 m4_rename_m4([decr])
-m4_undefine([divert])
 m4_rename_m4([divnum])
 m4_rename_m4([dumpdef])
 m4_rename_m4([errprint])
@@ -168,16 +167,21 @@ m4_rename_m4([sysval])
 m4_rename_m4([traceoff])
 m4_rename_m4([traceon])
 m4_rename_m4([translit])
-m4_undefine([undivert])
 
 # _m4_defn(ARG)
-# ----------------
+# -------------
 # _m4_defn is for internal use only - it bypasses the wrapper, so it
 # must only be used on one argument at a time, and only on macros
 # known to be defined.  Make sure this still works if the user renames
 # m4_defn but not _m4_defn.
 m4_copy([m4_defn], [_m4_defn])
 
+# _m4_divert_raw(NUM)
+# -------------------
+# _m4_divert_raw is for internal use only.  Use this instead of
+# m4_builtin([divert], NUM), so that tracing diversion flow is easier.
+m4_rename([divert], [_m4_divert_raw])
+
 # _m4_popdef(ARG...)
 # ------------------
 # _m4_popdef is for internal use only - it bypasses the wrapper, so it
@@ -192,6 +196,13 @@ m4_copy([m4_popdef], [_m4_popdef])
 # still works if the user renames m4_undefine but not _m4_undefine.
 m4_copy([m4_undefine], [_m4_undefine])
 
+# _m4_undivert(NUM...)
+# --------------------
+# _m4_undivert is for internal use only, and should always be given
+# arguments.  Use this instead of m4_builtin([undivert], NUM...), so
+# that tracing diversion flow is easier.
+m4_rename([undivert], [_m4_undivert])
+
 
 ## ------------------- ##
 ## 2. Error messages.  ##
@@ -1320,7 +1331,7 @@ m4_define([_m4_stack_reverse],
 # This works even inside m4_expand.
 m4_define([m4_cleardivert],
 [m4_if([$#], [0], [m4_fatal([$0: missing argument])],
-       [m4_builtin([divert], [-1])m4_undivert($@)m4_builtin([divert],
+       [_m4_divert_raw([-1])m4_undivert($@)_m4_divert_raw(
         _m4_divert(_m4_defn([_m4_divert_diversion])))])])
 
 
@@ -1364,7 +1375,7 @@ m4_define([m4_divert],
 [m4_popdef([_m4_divert_stack])]dnl
 [m4_define([_m4_divert_diversion], [$1])]dnl
 [m4_divert_stack_push([$0], [$1])]dnl
-[m4_builtin([divert], _m4_divert([$1]))])
+[_m4_divert_raw(_m4_divert([$1]))])
 
 
 # m4_divert_push(DIVERSION-NAME)
@@ -1373,7 +1384,7 @@ m4_define([m4_divert],
 m4_define([m4_divert_push],
 [m4_divert_stack_push([$0], [$1])]dnl
 [m4_pushdef([_m4_divert_diversion], [$1])]dnl
-[m4_builtin([divert], _m4_divert([$1]))])
+[_m4_divert_raw(_m4_divert([$1]))])
 
 
 # m4_divert_pop([DIVERSION-NAME])
@@ -1389,7 +1400,7 @@ m4_define([m4_divert_pop],
 [_m4_popdef([_m4_divert_stack], [_m4_divert_diversion])]dnl
 [m4_ifdef([_m4_divert_diversion], [],
           [m4_fatal([too many m4_divert_pop])])]dnl
-[m4_builtin([divert], _m4_divert(_m4_defn([_m4_divert_diversion])))])
+[_m4_divert_raw(_m4_divert(_m4_defn([_m4_divert_diversion])))])
 
 
 # m4_divert_text(DIVERSION-NAME, CONTENT)
@@ -1425,7 +1436,7 @@ m4_define([_m4_divert_unsafe],
 # this should not be used to undivert files.
 m4_define([m4_undivert],
 [m4_if([$#], [0], [m4_fatal([$0: missing argument])],
-       [$#], [1], [m4_builtin([undivert], _m4_divert([$1]))],
+       [$#], [1], [_m4_undivert(_m4_divert([$1]))],
        [m4_map_args([$0], $@)])])
 
 
@@ -1930,17 +1941,14 @@ m4_bmatch([$0], [^AC_], [[AC_DEFUN]], [[m4_defun]])['d 
macro])])]],
 # This is called frequently, so minimize the number of macro invocations
 # by avoiding dnl and other overhead on the common path.
 m4_define([_m4_require_call],
-m4_do([[m4_define([_m4_divert_grow], m4_decr(_m4_divert_grow))]],
-      [[m4_divert_push(_m4_divert_grow)]],
-      [[m4_default([$2], [$1])
-m4_provide_if([$1],
-             [],
-             [m4_warn([syntax],
-                      [$1 is m4_require'd but not m4_defun'd])])]],
-      [[m4_builtin([divert], _m4_divert($3))]],
-      [[m4_builtin([undivert], _m4_divert_grow)]],
-      [[m4_divert_pop(_m4_divert_grow)]],
-      [[m4_define([_m4_divert_grow], m4_incr(_m4_divert_grow))]]))
+[m4_pushdef([_m4_divert_grow], m4_decr(_m4_divert_grow))]dnl
+[m4_divert_push(_m4_divert_grow)]dnl
+[m4_if([$2], [], [$1], [$2])
+m4_provide_if([$1], [], [m4_warn([syntax],
+  [$1 is m4_require'd but not m4_defun'd])])]dnl
+[_m4_divert_raw(_m4_divert($3))]dnl
+[_m4_undivert(_m4_divert_grow)]dnl
+[m4_divert_pop(_m4_divert_grow)_m4_popdef([_m4_divert_grow])])
 
 
 # _m4_divert_grow
-- 
1.6.0.4