Dpkg::Substvars: Add automatic variable tracking

This makes the code more clear and does not require to explicitly list
the variables on output.

debian/changelog

@@ -72,6 +72,8 @@ dpkg (1.17.11) UNRELEASED; urgency=low
     dpkg-dev and gcc. Closes: #751363
   * Update i386 architecture GNU cpu regex in cputable to match i786 too.
   * Remove unused pkglibdir variable from libdpkg.pc.in.
+  * Perl modules:
+    - Add new set_as_auto() method to Dpkg::Substvars.
 
   [ Updated programs translations ]
   * Danish (Joe Dalton). Closes: #754127

scripts/Dpkg/Control/HashCore.pm

@@ -397,7 +397,7 @@ sub apply_substvars {
 
     # Add substvars to refer to other fields
     foreach my $f (keys %$self) {
-        $substvars->set_as_used("F:$f", $self->{$f});
+        $substvars->set_as_auto("F:$f", $self->{$f});
     }
 
     foreach my $f (keys %$self) {

scripts/Dpkg/Substvars.pm

@@ -19,7 +19,7 @@ package Dpkg::Substvars;
 use strict;
 use warnings;
 
-our $VERSION = '1.02';
+our $VERSION = '1.03';
 
 use Dpkg ();
 use Dpkg::Arch qw(get_host_arch);
@@ -48,6 +48,7 @@ strings.
 
 use constant {
     SUBSTVAR_ATTR_USED => 1,
+    SUBSTVAR_ATTR_AUTO => 2,
 };
 
 =head1 METHODS
@@ -85,7 +86,7 @@ sub new {
     $self->{vars}{'dpkg:Upstream-Version'} =~ s/-[^-]+$//;
     bless $self, $class;
 
-    my $attr = SUBSTVAR_ATTR_USED;
+    my $attr = SUBSTVAR_ATTR_USED | SUBSTVAR_ATTR_AUTO;
     $self->{attr}{$_} = $attr foreach keys %{$self->{vars}};
     if ($arg) {
         $self->load($arg) if -e $arg;
@@ -121,6 +122,19 @@ sub set_as_used {
     $self->set($key, $value, SUBSTVAR_ATTR_USED);
 }
 
+=item $s->set_as_auto($key, $value)
+
+Add/replace a substitution and mark it as used and automatic (no warnings
+will be produced even if unused).
+
+=cut
+
+sub set_as_auto {
+    my ($self, $key, $value) = @_;
+
+    $self->set($key, $value, SUBSTVAR_ATTR_USED | SUBSTVAR_ATTR_AUTO);
+}
+
 =item $s->get($key)
 
 Get the value of a given substitution.
@@ -217,7 +231,7 @@ sub set_version_substvars {
     my $upstreamversion = $sourceversion;
     $upstreamversion =~ s/-[^-]*$//;
 
-    my $attr = SUBSTVAR_ATTR_USED;
+    my $attr = SUBSTVAR_ATTR_USED | SUBSTVAR_ATTR_AUTO;
 
     $self->set('binary:Version', $binaryversion, $attr);
     $self->set('source:Version', $sourceversion, $attr);
@@ -238,7 +252,7 @@ This will never be warned about when unused.
 sub set_arch_substvars {
     my ($self) = @_;
 
-    my $attr = SUBSTVAR_ATTR_USED;
+    my $attr = SUBSTVAR_ATTR_USED | SUBSTVAR_ATTR_AUTO;
 
     $self->set('Arch', get_host_arch(), $attr);
 }
@@ -336,7 +350,7 @@ sub output {
     my $str = '';
     # Store all non-automatic substitutions only
     foreach my $vn (sort keys %{$self->{vars}}) {
-	next if /^(?:(?:dpkg|source|binary):(?:Source-)?Version|Space|Tab|Newline|Arch|Source-Version|F:.+)$/;
+	next if $self->{attr}{$vn} & SUBSTVAR_ATTR_AUTO;
 	my $line = "$vn=" . $self->{vars}{$vn} . "\n";
 	print { $fh } $line if defined $fh;
 	$str .= $line;
@@ -348,6 +362,10 @@ sub output {
 
 =head1 CHANGES
 
+=head2 Version 1.03
+
+New method: $s->set_as_auto().
+
 =head2 Version 1.02
 
 New argument: Accept a $binaryversion in $s->set_version_substvars(),