Re: AM_PROG_CC_C_O assumption

[Alexandre Duret-Lutz]

Hi Ralf,

>>> "RW" == Ralf Wildenhues <address@hidden> writes:

 RW> CVS Automake assumes that, as soon as per-target compile flags are used,
 RW> AM_PROG_CC_C_O is necessary.

Not exactly : it assumes that AM_PROG_CC_C_O is necessary as
soon as -c and -o are used.  Automake has always used -c -o for
per-target compile flags as well as for subdir-objects, however
previous versions of Automake forgot to require AM_PROG_CC_C_O
in the former case (but did in the letter).

 RW> Strictly speaking, this assumption is
 RW> correct: automake can't tell that there won't be a clash in object file
 RW> names.  And the user shouldn't be able to know, since the mapping of
 RW> source file names to object file names is an undocumented internal.

 RW> However, in practice there are many Makefile.am's out there that use
 RW> target_CFLAGS and such, and will definitely never have name conflicts

This means we don't have to rename the objects file in all
cases.  I agree, but it's seem too hard to tell.  Since
currently Automake always uses -c -o in this case, the presence
or absence of conflicts isn't a justification against or for
AM_PROG_CC_C_O.

 RW> and/or never possibly be used by a losing compiler.  

Definitely.

 RW> And as such I think it is too harsh to have Automake fail
 RW> hard in this case; giving a warning would be sufficient
 RW> IMVHO.

OK, let's turn in into a portability warning.  And since
portability warnings have been waiting to be turned on for three
years now, let's do that too.  I'm installing the following two
patches.

 RW> For example, the modular Xorg tree would need hundreds of changes to get
 RW> working, most of them actually in Makefile.am's that build only one
 RW> object.  A failure due to Automake upgrade will be perceived as an
 RW> Automake regression.  (Nevertheless, I intend to bring this issue to
 RW> their attention, after hearing your opinion about it.)

I'm not sure why the changes need to be in Makefile.ams.  Why not add
AM_PROG_CC_C_O to configure.ac?


2006-03-10  Alexandre Duret-Lutz  <address@hidden>

        * lib/Automake/ChannelDefs.pm: Make -Wportability the default in
        gnu and gnits modes.
        * doc/automake.texi (Invoking Automake): Adjust.

Index: NEWS
===================================================================
RCS file: /cvs/automake/automake/NEWS,v
retrieving revision 1.301
diff -u -r1.301 NEWS
--- NEWS        29 Jan 2006 17:35:12 -0000      1.301
+++ NEWS        10 Mar 2006 10:23:17 -0000
@@ -93,6 +93,10 @@
     that have been declared as programs in the same Makefile.
     This is mostly useful when some check_PROGRAMS are listed in TESTS.
 
+  - `-Wportability' has finally been turned on by default for `gnu' and
+    `gnits' strictness.  This means automake will complain about %-rules
+    or $(GNU Make functions) unless you switch to `foreign' strictness or
+    use `-Wno-portability'.
 
 New in 1.9:
 
Index: doc/automake.texi
===================================================================
RCS file: /cvs/automake/automake/doc/automake.texi,v
retrieving revision 1.130
diff -u -r1.130 automake.texi
--- doc/automake.texi   21 Feb 2006 20:29:25 -0000      1.130
+++ doc/automake.texi   10 Mar 2006 10:23:20 -0000
@@ -1253,12 +1253,8 @@
 variables.
 
 The categories output by default are @samp{syntax} and
address@hidden  Additionally, @samp{gnu} is enabled in @option{--gnu} and
address@hidden strictness.
-
address@hidden warnings are currently disabled by default, but they
-will be enabled in @option{--gnu} and @option{--gnits} strictness in a
-future release.
address@hidden  Additionally, @samp{gnu} and @samp{portability}
+are enabled in @option{--gnu} and @option{--gnits} strictness.
 
 @vindex WARNINGS
 The environment variable @env{WARNINGS} can contain a comma separated
Index: lib/Automake/ChannelDefs.pm
===================================================================
RCS file: /cvs/automake/automake/lib/Automake/ChannelDefs.pm,v
retrieving revision 1.3
diff -u -r1.3 ChannelDefs.pm
--- lib/Automake/ChannelDefs.pm 14 May 2005 20:28:51 -0000      1.3
+++ lib/Automake/ChannelDefs.pm 10 Mar 2006 10:23:20 -0000
@@ -1,4 +1,4 @@
-# Copyright (C) 2002, 2003 Free Software Foundation, Inc.
+# Copyright (C) 2002, 2003, 2006 Free Software Foundation, Inc.
 
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -324,29 +324,12 @@
 {
   my ($name) = @_;
 
-  # FIXME: 'portability' warnings are currently disabled by default.
-  # Eventually we want to turn them on in GNU and GNITS modes, but
-  # we don't do this yet in Automake 1.7 to help the 1.6/1.7 transition.
-  #
-  # Indeed there would be only two ways to get rid of these new warnings:
-  #  1. adjusting Makefile.am
-  #     This is not always easy (or wanted).  Consider %-rules or
-  #     $(function args) variables.
-  #  2. using -Wno-portability
-  #     This means there is no way to have the same Makefile.am
-  #     working both with Automake 1.6 and 1.7 (since 1.6 does not
-  #     understand -Wno-portability).
-  #
-  # In Automake 1.8 (or whatever it is called) we can turn these
-  # warnings on, since -Wno-portability will not be an issue for
-  # the 1.7/1.8 transition.
-
   if ($name eq 'gnu')
     {
       setup_channel 'error-gnu', silent => 0;
       setup_channel 'error-gnu/warn', silent => 0, type => 'error';
       setup_channel 'error-gnits', silent => 1;
-      # setup_channel 'portability', silent => 0;
+      setup_channel 'portability', silent => 0;
       setup_channel 'gnu', silent => 0;
     }
   elsif ($name eq 'gnits')
@@ -354,7 +337,7 @@
       setup_channel 'error-gnu', silent => 0;
       setup_channel 'error-gnu/warn', silent => 0, type => 'error';
       setup_channel 'error-gnits', silent => 0;
-      # setup_channel 'portability', silent => 0;
+      setup_channel 'portability', silent => 0;
       setup_channel 'gnu', silent => 0;
     }
   elsif ($name eq 'foreign')
@@ -362,7 +345,7 @@
       setup_channel 'error-gnu', silent => 1;
       setup_channel 'error-gnu/warn', silent => 0, type => 'warning';
       setup_channel 'error-gnits', silent => 1;
-      # setup_channel 'portability', silent => 1;
+      setup_channel 'portability', silent => 1;
       setup_channel 'gnu', silent => 1;
     }
   else


2006-03-10  Alexandre Duret-Lutz  <address@hidden>

        * automake.in (lang_c_rewrite): Make the AM_PROG_CC_C_O requirement
        a 'portability' warning, so that people can ignore it.  Suggested
        by Ralf Wildenhues.

Index: automake.in
===================================================================
RCS file: /cvs/automake/automake/automake.in,v
retrieving revision 1.1616
diff -u -r1.1616 automake.in
--- automake.in 29 Jan 2006 17:35:12 -0000      1.1616
+++ automake.in 10 Mar 2006 10:23:18 -0000
@@ -5242,7 +5242,8 @@
 
          # libtool is always able to put the object at the proper place,
          # so we do not have to require AM_PROG_CC_C_O when building .lo files.
-         err_var ($var, "compiling `$base.c' in subdir requires "
+         msg_var ('portabiliy', $var,
+                  "compiling `$base.c' in subdir requires "
                   . "`AM_PROG_CC_C_O' in `$configure_ac'",
                   uniq_scope => US_GLOBAL,
                   uniq_part => 'AM_PROG_CC_C_O subdir')
@@ -5265,7 +5266,8 @@
       && ! option 'subdir-objects'
       && $nonansi_obj ne '.lo')
     {
-      err_var ($var, "compiling `$base.c' with per-target flags requires "
+      msg_var ('portability',
+              $var, "compiling `$base.c' with per-target flags requires "
               . "`AM_PROG_CC_C_O' in `$configure_ac'",
               uniq_scope => US_GLOBAL,
               uniq_part => 'AM_PROG_CC_C_O per-target')
-- 
Alexandre Duret-Lutz

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