Re: m4_copy and m4_rename semantic changes

[Eric Blake]

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According to Ralf Wildenhues on 6/12/2009 12:28 AM:
>> Good point.  So, back to my other question - would you rather manually
>> undefine the pre-existing definitions at all usage points, or would you
>> rather that I create a new m4sugar macro m4_rename_force in autoconf 2.64
>> which performs the rename regardless of the defined-ness of the
>> destination, at which point your gcc patch would be s/m4_rename/&_force/
>> rather than adding a line of m4_undefine?
> 
> Well, I don't mind to have a m4_rename_force, but I would still add the
> m4_undefine everywhere, in order to have consistent code that can also
> be reused with older Autoconf (parts of the GCC tree are also used in
> other projects such as libffi, without the override code in ../config,
> and it is helpful not to have to force Autoconf version bump everywhere
> at the same time).

Or backport a definition of m4_rename_force up front for all autoconf
versions where it is not defined.

At any rate, here's what I'm committing.  I am willing to make a slight
change in semantics for m4_copy_force, if others want it:

m4_copy_force([undefined], [defined])

currently behaves as a synonym for m4_undefine([defined]), but I could see
it being useful to error out in this case.  m4_copy_force([undefined],
[undefined]) will remain a silent no-op, just like m4_copy.

This rewrite would be as simple as the following, if others think it is a
worthwhile change:

m4_define([m4_copy_force],
[m4_ifdef([$2], [m4_ifdef([$1], [_m4_undefine([$2])],
  [m4_fatal([$0: won't overwrite $2 with undefined $1])])])m4_copy($@)])

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

Eric Blake             address@hidden
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>From 4297bd715463cb87b0196811e3c51e42f37218a8 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Mon, 15 Jun 2009 06:49:58 -0600
Subject: [PATCH] Add m4_copy_force, m4_rename_force.

* lib/m4sugar/m4sugar.m4 (m4_copy_force, m4_rename_force): New
macros.
* tests/m4sugar.at (m4@&address@hidden): Test them.
* doc/autoconf.texi (Redefined M4 Macros) <m4_copy>: Document
them.
* NEWS: Likewise.
Suggested by Ralf Wildenhues.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog              |    9 +++++++++
 NEWS                   |    4 ++--
 doc/autoconf.texi      |   19 +++++++++++++------
 lib/m4sugar/m4sugar.m4 |   16 +++++++++++++++-
 tests/m4sugar.at       |   12 +++++++++++-
 5 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 0375ff4..f4605db 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2009-06-15  Eric Blake  <address@hidden>

+       Add m4_copy_force, m4_rename_force.
+       * lib/m4sugar/m4sugar.m4 (m4_copy_force, m4_rename_force): New
+       macros.
+       * tests/m4sugar.at (m4@&address@hidden): Test them.
+       * doc/autoconf.texi (Redefined M4 Macros) <m4_copy>: Document
+       them.
+       * NEWS: Likewise.
+       Suggested by Ralf Wildenhues.
+
        Reinstate _AC_CHECK_HEADER_OLD for gcc.
        * lib/autoconf/headers.m4 (_AC_CHECK_HEADER_NEW)
        (_AC_CHECK_HEADER_OLD): Provide autoupdate versions, since gcc and
diff --git a/NEWS b/NEWS
index 82ba635..93a09c9 100644
--- a/NEWS
+++ b/NEWS
@@ -26,8 +26,8 @@ GNU Autoconf NEWS - User visible changes.
    AT_CHECK_UNQUOTED

 ** The following documented m4sugar macros are new:
-   m4_argn  m4_default_nblank  m4_default_nblank_quoted  m4_ifblank
-   m4_ifnblank
+   m4_argn  m4_copy_force  m4_default_nblank  m4_default_nblank_quoted
+   m4_ifblank  m4_ifnblank  m4_rename_force

 * Major changes in Autoconf 2.63b (2009-03-31) [beta]
   Released by Eric Blake, based on git versions 2.63.*.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 9e3327e..4b08042 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -10642,16 +10642,23 @@ Redefined M4 Macros
 @end defmac

 @defmac m4_copy (@var{source}, @var{dest})
address@hidden m4_copy_force (@var{source}, @var{dest})
 @defmacx m4_rename (@var{source}, @var{dest})
address@hidden m4_rename_force (@var{source}, @var{dest})
 @msindex{copy}
address@hidden
 @msindex{rename}
address@hidden
 These macros aren't directly builtins, but are closely related to
address@hidden and @code{m4_defn}.  They both ensure that @var{dest}
-is undefined, then proceed to copy the entire pushdef stack of
-definitions of @var{source}.  @code{m4_copy} preserves the source
-(including in the special case where @var{source} is undefined), while
address@hidden undefines the original macro name (making it an error
-to rename an undefined @var{source}).
address@hidden and @code{m4_defn}.  @code{m4_copy} and
address@hidden ensure that @var{dest} is undefined, while
address@hidden and @code{m4_rename_force} overwrite any existing
+definition.  All four macros then proceed to copy the entire pushdef
+stack of definitions of @var{source} over to @var{dest}.  @code{m4_copy}
+and @code{m4_copy_force} preserve the source (including in the special
+case where @var{source} is undefined), while @code{m4_rename} and
address@hidden undefine the original macro name (making it an
+error to rename an undefined @var{source}).

 Note that attempting to invoke a renamed macro might not work, since the
 macro may have a dependence on helper macros accessed via composition of
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index f5a1f1c..83f6dba 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -579,7 +579,8 @@ m4_define([_m4_bpatsubsts],
 # give an error if DST is already defined.  This is particularly nice
 # for copying self-modifying pushdef stacks, where the top definition
 # includes one-shot initialization that is later popped to the normal
-# definition.
+# definition.  This version intentionally does nothing if SRC is
+# undefined.
 #
 # Some macros simply can't be renamed with this method: namely, anything
 # involved in the implementation of m4_stack_foreach_sep.
@@ -589,6 +590,19 @@ m4_define([m4_copy],
 [m4_ifdef([m4_location($1)], [m4_define([m4_location($2)], m4_location)])])


+# m4_copy_force(SRC, DST)
+# m4_rename_force(SRC, DST)
+# -------------------------
+# Like m4_copy/m4_rename, except blindly overwrite any existing DST.
+# Note that m4_copy_force tolerates undefined SRC, while m4_rename_force
+# does not.
+m4_define([m4_copy_force],
+[m4_ifdef([$2], [_m4_undefine([$2])])m4_copy($@)])
+
+m4_define([m4_rename_force],
+[m4_ifdef([$2], [_m4_undefine([$2])])m4_rename($@)])
+
+
 # m4_define_default(MACRO, VALUE)
 # -------------------------------
 # If MACRO is undefined, set it to VALUE.
diff --git a/tests/m4sugar.at b/tests/m4sugar.at
index 4bc7bd4..04f06b9 100644
--- a/tests/m4sugar.at
+++ b/tests/m4sugar.at
@@ -104,7 +104,8 @@ AT_CLEANUP

 AT_SETUP([m4@&address@hidden)

-AT_KEYWORDS([m4@&address@hidden m4@&address@hidden m4@&address@hidden 
m4@&address@hidden)
+AT_KEYWORDS([m4@&address@hidden m4@&address@hidden m4@&address@hidden 
m4@&address@hidden
+m4@&address@hidden m4@&address@hidden)

 # Ensure that m4sugar dies when dereferencing undefined macros, whether
 # this is provided by m4 natively or faked by wrappers in m4sugar.
@@ -161,12 +162,21 @@ m4_popdef([b], [c])dnl
 a b c
 dnl m4_copy is intentionally a no-op on undefined source
 m4_copy([oops], [dummy])m4_ifdef([dummy], [[oops]])dnl
+dnl allow forceful overwrites
+m4_define([d], [4])m4_define([e], [5])m4_define([f], [6])dnl
+m4_copy_force([d], [e])dnl
+m4_rename_force([d], [f])dnl
+d e f
+m4_popdef([e], [f])dnl
+d e f
 ]], [[0 b c
 a 0 c
 a 0 0
 a 2 2
 a 1 1
 a b c
+d 4 4
+d e f
 ]])

 AT_CLEANUP
-- 
1.6.3.rc3.2.g4b51