no way to redefine variables in automake

[Johan Danielsson]

Hi,

This code fails:

--foo.am
SOMETHING=x

--Makefile.am--
include foo.am
SOMETHING=y

This seems like a silly thing to do, but can be quite handy if you
want to provide a default for some variable. The same thing can be
accomplished with AC_SUBST instead, but I don't think that's very
elegant.

Fix: either just remove the test for multiple definition, or add some
way to make an assignment optional. Crude example follows:

--- automake.save       Mon Mar 18 17:32:12 2002
+++ automake    Mon Mar 18 18:11:56 2002
@@ -142,7 +142,7 @@
 # leading tabs here then we need to make the reader smarter, because
 # otherwise it will think rules like `foo=bar; \' are errors.
 my $MACRO_PATTERN = 'address@hidden';
-my $ASSIGNMENT_PATTERN = '^ *([^ \t=:+]*)\s*([:+]?)=\s*(.*)$';
+my $ASSIGNMENT_PATTERN = '^ *([^ \t?=:+]*)\s*([?:+]?)=\s*(.*)$';
 # This pattern recognizes a Gnits version id and sets $1 if the
 # release is an alpha release.  We also allow a suffix which can be
 # used to extend the version number with a "fork" identifier.
@@ -5939,12 +5939,18 @@
 sub macro_define ($$$$$$)
 {
   my ($var, $var_is_am, $type, $cond, $value, $where) = @_;
+  my ($old_type);
 
   file_error ($where, "bad macro name `$var'")
     if $var !~ /$MACRO_PATTERN/o;
 
   $cond ||= 'TRUE';
 
+  # If already set, and this is an optional, just ignore
+  if(defined $var_type{$var} && $type eq '?') {
+      return;
+  }
+
   # An Automake variable must be consistently defined with the same
   # sign by Automake.  A user variable must be set by either `=' or
   # `:=', and later promoted to `+='.
@@ -5964,6 +5970,8 @@
          file_error ($where, "$var must be set with `=' before using `+='");
        }
     }
+
+  $old_type = defined $var_type{$var} ? $var_type{$var} : '';
   $var_type{$var} = $type;
 
   # When adding, since we rewrite, don't try to preserve the
@@ -5994,7 +6002,7 @@
       # the original location.  More subs are needed to handle
       # properly variables.  Once this done, remove this hack.
       $var_location{$var} = $where
-       unless defined $var_location{$var};
+       unless defined $var_location{$var} and $old_type ne '?';
 
       # If Automake tries to override a value specified by the user,
       # just don't let it do.
@@ -6013,6 +6021,7 @@
          # an Automake variable or an AC_SUBST variable.
          check_ambiguous_conditional ($var, $cond)
            unless ($var_is_am{$var} && !$var_is_am
+                   || $old_type eq '?'
                    || exists $configure_vars{$var});
 
          $var_value{$var}{$cond} = $value;


This allows this syntax:

--foo.am
SOMETHING?=x

--Makefile.am--
include foo.am
SOMETHING=y