Regularise and comment access_cfg

diff --git a/dgit b/dgit
index 59f7a73fff792000c678e23fcc89d761943ebe01..3c311400afeaec6ef64dccc64cbc5a4129e59c66 100755 (executable)
--- a/dgit
+++ b/dgit
@@ -574,7 +574,7 @@ sub access_basedistro () {
 }
 
 sub access_quirk () {
-    # returns (quirk name, distro to use instead, quirk-specific info)
+    # returns (quirk name, distro to use instead or undef, quirk-specific info)
     my $basedistro = access_basedistro();
     my $backports_quirk = cfg("dgit-distro.$basedistro.backports-quirk",
                              'RETURN-UNDEF');
@@ -588,22 +588,52 @@ sub access_quirk () {
            return ('backports',"$basedistro-backports",$1);
        }
     }
-    return ('none',$basedistro);
+    return ('none',undef);
 }
 
-sub access_distro () {
-    return (access_quirk())[1];
+sub access_distros () {
+    # Returns list of distros to try, in order
+    #
+    # We want to try:
+    #    1. the access_quirk distro, if any
+    #    2a. the user's specified distro, or failing that  } basedistro
+    #    2b. the distro calculated from the suite          }
+    my @l = access_basedistro();
+
+    my (undef,$quirkdistro) = access_quirk();
+    unshift @l, $quirkdistro if defined $quirkdistro;
+
+    return @l;
 }
 
 sub access_cfg (@) {
     my (@keys) = @_;
-    my $basedistro = access_basedistro();
-    my $distro = $idistro || access_distro();
-    my $value = cfg(map {
-       ("dgit-distro.$distro.$_",
-        "dgit-distro.$basedistro.$_",
-        "dgit.default.$_")
-                   } @keys);
+    my @cfgs;
+    # The nesting of these loops determines the search order.  We put
+    # the key loop on the outside so that we search all the distros
+    # for each key, before going on to the next key.  That means that
+    # if access_cfg is called with a more specific, and then a less
+    # specific, key, an earlier distro can override the less specific
+    # without necessarily overriding any more specific keys.  (If the
+    # distro wants to override the more specific keys it can simply do
+    # so; whereas if we did the loop the other way around, it would be
+    # impossible to for an earlier distro to override a less specific
+    # key but not the more specific ones without restating the unknown
+    # values of the more specific keys.
+    my @realkeys;
+    my @rundef;
+    # We have to deal with RETURN-UNDEF specially, so that we don't
+    # terminate the search prematurely.
+    foreach (@keys) {
+       if (m/RETURN-UNDEF/) { push @rundef, $_; last; }
+       push @realkeys, $_
+    }
+    foreach my $d (access_distros()) {
+       push @cfgs, map { "dgit-distro.$d.$_" } @realkeys;
+    }
+    push @cfgs, map { "dgit.default.$_" } @realkeys;
+    push @cfgs, @rundef;
+    my $value = cfg(@cfgs);
     return $value;
 }