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Re: Use "$(MKDIR_P) sys", not race-prone "test -d sys || mkdir sys".

From: Ralf Wildenhues
Subject: Re: Use "$(MKDIR_P) sys", not race-prone "test -d sys || mkdir sys".
Date: Mon, 22 Jan 2007 19:45:02 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

Hello Jim, all,

* Jim Meyering wrote on Mon, Jan 22, 2007 at 03:52:21PM CET:
>     dnl Do special magic for MKDIR_P instead of AC_SUBST, to get
>     dnl relative names right.
> The only case I can imagine is when MKDIR_P is specified
> as e.g., MKDIR_P='../build-aux/install-sh -d' in one place,
> and later (in another Makefile) as
> MKDIR_P='somewhere/else/install-sh -d' in another.
> I wonder which use case made it so using AC_SUBST wasn't an option.

The AC_SUBST is actually harmless.  It adds a couple of unneeded
lines to the configure script, but config.status is written in a way
that the special magic happens before the regular substitutions, so
that latter bit will actually be a noop.

This issue is unfortunate.  It arises because at the same time we
changed it, also the logic of automake to trace the macro AC_SUBST_TRACE
rather than AC_SUBST directly was changed; which is why Automake-1.10
works fine but older doesn't.  I tested CVS Autoconf with older
(non-CVS) Automake versions back then, which is why I originally
suggested using a different name (MKDIR_P rather than mkdir_p);
but I did not test using the newer Autoconf macro AC_PROG_MKDIR_P in
conjunction with the older Automake.  Sorry about that.

Autoconf could consider adding AC_SUBST([MKDIR_P]); it will cause an
extraneous line in the configure script, but should be harmless
otherwise, as far as I can see it.  But surely people could update
to Automake 1.10 just as well, given the number of bugs it has fixed
over 1.9.6.

OK to apply?


2007-01-22  Ralf Wildenhues  <address@hidden>

        * lib/autoconf/programs.m4 (AC_PROG_MKDIR_P): Also
        AC_SUBST([MKDIR_P]), so that Automake < 1.10 will pick up its
        trace, if a package uses AC_PROG_MKDIR_P explicitly.  The actual
        substitution will still be done by the special code.
        Report by Jim Meyering.

Index: lib/autoconf/programs.m4
RCS file: /cvsroot/autoconf/autoconf/lib/autoconf/programs.m4,v
retrieving revision 1.64
diff -u -r1.64 programs.m4
--- lib/autoconf/programs.m4    11 Jan 2007 21:17:37 -0000      1.64
+++ lib/autoconf/programs.m4    22 Jan 2007 19:36:23 -0000
@@ -682,8 +682,12 @@
     MKDIR_P="$ac_install_sh -d"
-dnl Do special magic for MKDIR_P instead of AC_SUBST, to get
-dnl relative names right.
+dnl In status.m4, we di special magic for MKDIR_P instead of AC_SUBST,
+dnl to get relative names right.  However, here we also AC_SUBST, so
+dnl that Automake versions before 1.10 will pick it up (they do not
+dnl trace AC_SUBST_TRACE).
+dnl FIXME: Remove this once we drop support for Automake < 1.10.

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