AM_SUBST_IGNORE = AC_SUBST without Makefile variable definition

[Alexandre Duret-Lutz]

Occasionally we want to disable automatic variable definitions
of AC_SUBSTitutions.  Two cases were already hardcoded into
automake (AMDEPBACKSLASH and ANSI2KNR). I had been considering
adding such a feature since Autoconf introduced multiline
AC_SUBSTitutions.  Now I think Ralf's suggestion in PR/477 makes
it even more relevant.

Any thought ?

2005-10-17  Alexandre Duret-Lutz  <address@hidden>

        * automake.in (%ignored_configure_vars): New variable.
        (scan_autoconf_traces): Scan for AM_SUBST_IGNORE_TRACE and fill
        %ignored_configure_vars.
        (define_configure_variable): Declare ignored configure variables
        as VAR_SILENT.  Do not special-case AMDEPBACKSLASH and ANSI2KNR
        w.r.t. VAR_SILENT.
        * doc/automake.texi (Optional): Document AM_SUBST_IGNORE.
        * m4/substign.m4: New file.
        * m4/Makefile.am (dist_m4data_DATA): Add substign.m4.
        * m4/cond.m4: AM_SUBST_IGNORE $1_TRUE and $1_FALSE (PR automake/477).
        * m4/depend.m4: AM_SUBST_IGNORE AMDEPBACKSLASH.
        * m4/protos.m4: AM_SUBST_IGNORE ANSI2KNR.
        * tests/cond.test: Make sure TEST_FALSE and TEST_TRUE are not defined.

Index: NEWS
===================================================================
RCS file: /cvs/automake/automake/NEWS,v
retrieving revision 1.300
diff -u -r1.300 NEWS
--- NEWS        14 May 2005 20:28:50 -0000      1.300
+++ NEWS        17 Oct 2005 20:35:43 -0000
@@ -89,6 +89,10 @@
     $(LIBOBJS), $(LTLIBOBJS), $(ALLOCA), and $(LTALLOCA) can be used
     in different directories.
 
+  - New macro: AM_SUBST_IGNORE.  It works like AC_SUBST, except Automake
+    will not produce a `VAR = @VAR@' definition in Makefile.in.  This comes
+    handy when @VAR@ ends with a backslash, contains multiple lines, or
+    if the definition simply bloats the Makefile.in.
 
 New in 1.9:
 
Index: automake.in
===================================================================
RCS file: /cvs/automake/automake/automake.in,v
retrieving revision 1.1613
diff -u -r1.1613 automake.in
--- automake.in 3 Oct 2005 20:52:27 -0000       1.1613
+++ automake.in 17 Oct 2005 20:35:44 -0000
@@ -390,6 +390,10 @@
 # generation.
 my %configure_vars = ();
 
+# Ignored configure substitutions (i.e., variables not to be output in
+# Makefile.in)
+my %ignored_configure_vars = ();
+
 # Files included by $configure_ac.
 my @configure_deps = ();
 
@@ -4771,6 +4775,7 @@
                AM_INIT_AUTOMAKE => 0,
                AM_MAINTAINER_MODE => 0,
                AM_PROG_CC_C_O => 0,
+                AM_SUBST_IGNORE_TRACE => 1,
                LT_SUPPORTED_TAG => 1,
                _LT_AC_TAGCONFIG => 0,
                m4_include => 1,
@@ -4882,6 +4887,12 @@
        {
          $libsources{$args[1]} = $here;
        }
+      elsif ($macro eq 'AC_REQUIRE_AUX_FILE')
+       {
+          # Only remember the first time a file is required.
+         $required_aux_file{$args[1]} = $where
+            unless exists $required_aux_file{$args[1]};
+       }
       elsif ($macro eq 'AC_SUBST_TRACE')
        {
          # Just check for alphanumeric in AC_SUBST_TRACE.  If you do
@@ -4939,11 +4950,9 @@
        {
          $seen_cc_c_o = $where;
        }
-      elsif ($macro eq 'AC_REQUIRE_AUX_FILE')
+      elsif ($macro eq 'AM_SUBST_IGNORE_TRACE')
        {
-          # Only remember the first time a file is required.
-         $required_aux_file{$args[1]} = $where
-            unless exists $required_aux_file{$args[1]};
+         $ignored_configure_vars{$args[1]} = $where;
        }
       elsif ($macro eq 'm4_include'
             || $macro eq 'm4_sinclude'
@@ -5835,16 +5844,16 @@
   my $pretty = VAR_ASIS;
   my $owner = VAR_CONFIGURE;
 
-  # Do not output the ANSI2KNR configure variable -- we AC_SUBST
-  # it in protos.m4, but later redefine it elsewhere.  This is
-  # pretty hacky.  We also don't output AMDEPBACKSLASH: it might
-  # be subst'd by `\', which certainly would not be appreciated by
-  # Make.
-  if ($var eq 'ANSI2KNR' || $var eq 'AMDEPBACKSLASH')
-    {
-      $pretty = VAR_SILENT;
-      $owner = VAR_AUTOMAKE;
-    }
+  # Some variables we do not want to output.  For instance it
+  # would be a bad idea to output `U = @address@hidden when address@hidden@` 
can be
+  # substituted as `\`.
+  $pretty = VAR_SILENT if exists $ignored_configure_vars{$var};
+
+  # ANSI2KNR is a variable that Automake wants to redefine, so
+  # it must be owned by Automake.  (It is also used as a proof
+  # that AM_C_PROTOTYPES has been run, that's why we do not simply
+  # omit the AC_SUBST.)
+  $owner = VAR_AUTOMAKE if $var eq 'ANSI2KNR';
 
   Automake::Variable::define ($var, $owner, '', TRUE, subst $var,
                              '', $configure_vars{$var}, $pretty);
Index: doc/automake.texi
===================================================================
RCS file: /cvs/automake/automake/doc/automake.texi,v
retrieving revision 1.122
diff -u -r1.122 automake.texi
--- doc/automake.texi   13 Sep 2005 23:14:55 -0000      1.122
+++ doc/automake.texi   17 Oct 2005 20:35:45 -0000
@@ -1588,6 +1588,9 @@
 you can use these variables in any @file{Makefile.am} if
 @code{AC_PATH_XTRA} is called.
 
address@hidden (see below) can be used to declare
+substitutions that should not be defined as @file{Makefile} variables.
+
 @item AM_C_PROTOTYPES
 This is required when using automatic de-ANSI-fication; see @ref{ANSI}.
 
@@ -1606,6 +1609,16 @@
 @code{MAINTAINER_MODE} conditional, which you can use in your own
 @file{Makefile.am}.  @xref{maintainer-mode}.
 
address@hidden AM_SUBST_IGNORE
+This is similar to and uses the same syntax as @code{AC_SUBST} (see
+above), except @command{automake} will not output a definition of the
+variable in any @file{Makefile.in} it produces.
+
+It is occasionally necessary to let Automake ignore some substitutions
+that are not meant to be used as @file{Makefile} variables.  For
+instance values that are terminated by a backslash would cause syntax
+error is they were defined as @file{Makefile} variables.
+
 @item m4_include
 Files included by @file{configure.ac} using this macro will be
 detected by Automake and automatically distributed.  They will also
Index: m4/Makefile.am
===================================================================
RCS file: /cvs/automake/automake/m4/Makefile.am,v
retrieving revision 1.54
diff -u -r1.54 Makefile.am
--- m4/Makefile.am      14 May 2005 20:28:53 -0000      1.54
+++ m4/Makefile.am      17 Oct 2005 20:35:45 -0000
@@ -2,7 +2,7 @@
 
 ## Makefile for Automake m4.
 
-## Copyright (C) 1996, 1997, 1998, 1999, 2001, 2002, 2003, 2004
+## Copyright (C) 1996, 1997, 1998, 1999, 2001, 2002, 2003, 2004, 2005
 ## Free Software Foundation, Inc.
 
 ## This program is free software; you can redistribute it and/or modify
@@ -54,6 +54,7 @@
 runlog.m4 \
 sanity.m4 \
 strip.m4 \
+substign.m4 \
 tar.m4
 
 EXTRA_DIST = dirlist amversion.in
Index: m4/cond.m4
===================================================================
RCS file: /cvs/automake/automake/m4/cond.m4,v
retrieving revision 1.13
diff -u -r1.13 cond.m4
--- m4/cond.m4  9 Jan 2005 14:46:21 -0000       1.13
+++ m4/cond.m4  17 Oct 2005 20:35:45 -0000
@@ -16,8 +16,8 @@
 [AC_PREREQ(2.52)dnl
  ifelse([$1], [TRUE],  [AC_FATAL([$0: invalid condition: $1])],
        [$1], [FALSE], [AC_FATAL([$0: invalid condition: $1])])dnl
-AC_SUBST([$1_TRUE])
-AC_SUBST([$1_FALSE])
+AM_SUBST_IGNORE([$1_TRUE])
+AM_SUBST_IGNORE([$1_FALSE])
 if $2; then
   $1_TRUE=
   $1_FALSE='#'
Index: m4/depend.m4
===================================================================
RCS file: /cvs/automake/automake/m4/depend.m4,v
retrieving revision 1.35
diff -u -r1.35 depend.m4
--- m4/depend.m4        9 Jan 2005 14:46:21 -0000       1.35
+++ m4/depend.m4        17 Oct 2005 20:35:45 -0000
@@ -152,5 +152,5 @@
   AMDEPBACKSLASH='\'
 fi
 AM_CONDITIONAL([AMDEP], [test "x$enable_dependency_tracking" != xno])
-AC_SUBST([AMDEPBACKSLASH])
+AM_SUBST_IGNORE([AMDEPBACKSLASH])
 ])
Index: m4/protos.m4
===================================================================
RCS file: /cvs/automake/automake/m4/protos.m4,v
retrieving revision 1.11
diff -u -r1.11 protos.m4
--- m4/protos.m4        9 Jan 2005 14:46:21 -0000       1.11
+++ m4/protos.m4        17 Oct 2005 20:35:45 -0000
@@ -20,9 +20,9 @@
 fi
 # Ensure some checks needed by ansi2knr itself.
 AC_REQUIRE([AC_HEADER_STDC])
-AC_CHECK_HEADERS(string.h)
-AC_SUBST(U)dnl
-AC_SUBST(ANSI2KNR)dnl
+AC_CHECK_HEADERS([string.h])
+AC_SUBST([U])dnl
+AM_SUBST_IGNORE([ANSI2KNR])dnl
 ])
 
 AU_DEFUN([fp_C_PROTOTYPES], [AM_C_PROTOTYPES])
Index: m4/substign.m4
===================================================================
RCS file: m4/substign.m4
diff -N m4/substign.m4
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ m4/substign.m4      17 Oct 2005 20:35:45 -0000
@@ -0,0 +1,22 @@
+##                                                          -*- Autoconf -*-
+# Copyright (C) 2005  Free Software Foundation, Inc.
+#
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# AM_SUBST_IGNORE(VARIABLE, [VALUE])
+# ----------------------------------
+# AC_SUBST the VARIABLE, but do not output
+# VARIABLE = @VARIABLE@ in Makefile.in.
+AC_DEFUN([AM_SUBST_IGNORE],
+[AC_SUBST($@)dnl
+AM_SUBST_IGNORE_TRACE([$1])])
+
+# AM_SUBST_IGNORE_TRACE(VARIABLE)
+# -------------------------------
+# Prevent Automake from outputing VARIABLE = @VARIABLE@ in Makefile.in.
+# Making this macro distinct from AM_SUBST_IGNORE makes it possible to
+# ignore variables that have been AC_SUBST_TRACEd without being AC_SUBSTed,
+# should we ever have to do that.
+AC_DEFUN([AM_SUBST_IGNORE_TRACE])
Index: tests/cond.test
===================================================================
RCS file: /cvs/automake/automake/tests/cond.test,v
retrieving revision 1.8
diff -u -r1.8 cond.test
--- tests/cond.test     14 May 2005 20:28:54 -0000      1.8
+++ tests/cond.test     17 Oct 2005 20:35:45 -0000
@@ -1,5 +1,5 @@
 #! /bin/sh
-# Copyright (C) 1997, 2001, 2002  Free Software Foundation, Inc.
+# Copyright (C) 1997, 2001, 2002, 2005  Free Software Foundation, Inc.
 #
 # This file is part of GNU Automake.
 #
@@ -22,6 +22,8 @@
 
 . ./defs || exit 1
 
+set -e
+
 cat > configure.in << 'END'
 AC_INIT
 AM_INIT_AUTOMAKE(nonesuch, nonesuch)
@@ -37,11 +39,10 @@
 endif
 END
 
-set -e
-$ACLOCAL || exit 1
+$ACLOCAL
 $AUTOMAKE
 
+grep '^TEST_FALSE' Makefile.in && exit 1
+grep '^TEST_TRUE' Makefile.in && exit 1
 grep 'address@hidden@VAR = true$' Makefile.in
 grep 'address@hidden@VAR = false$' Makefile.in
-
-exit 0


-- 
Alexandre Duret-Lutz

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