Tweak revert and verify change searches.

If change "foo" is reworked, and one says `revert --to foo`, does one want to
revert to the the most recent version of "foo", or to the earlist version of
"foo"? Sqitch has traditionally assumed the latter; this change implements
the former, and does the same for the `--to` option to `verify`.

This might be a bit controversial, however, because some folks might decide
the latter is the more expected case (especially since, if you really want the
latest version you can say `revert --to foo@HEAD`). So this change may well
get reversed pending consensus from the community.

Meanwhile, I also noticed that changes specified as "HEAD" or "ROOT" which are
supposed to be aliases for "@Head" and "@root" since v0.991, does not actually
work. This change fixes this issue, as well. This fix likely won't be
reverted, because frankly it has annoyed me for quite some time.

Changes

@@ -23,6 +23,15 @@ Revision history for Perl extension App::Sqitch
        ignores the target (#281).
      - The `--db-*` options are now more consistently applied to a target,
        including when the target is specified as a URI (#293).
+     - `HEAD` and `ROOT` are now properly recognized as aliases for `@HEAD` and
+       `@ROOT`, when querying the database, too. This was supposedly done in
+       v0.991, but due to a bug, it wasn't really. Sorry about that.
+     - The `revert` command will now search for the most recent variant of a
+       named change , rather than the earliest. This goes along with the
+       convention of earlier changes generally being referred to as of the tag
+       that follows them (#312).
+     - The `verify` command now looks for the most recent variant of a `--to`
+       change if it's not tag-qualified.
 
 0.9995 2016-07-27T09:23:55Z
      - Taught the `add` command not to ignore the `--change` option.

lib/App/Sqitch/Engine.pm

@@ -241,7 +241,8 @@ sub revert {
 
     if (defined $to) {
         my ($change) = $self->_load_changes(
-            $self->change_for_key($to)
+            # If no tag, default to HEAD to find most recent variant.
+            $self->find_change( tag => 'HEAD', $self->_params_for_key($to) )
         ) or do {
             # Not deployed. Is it in the plan?
             if ( $plan->get($to) ) {
@@ -394,7 +395,9 @@ sub _trim_to {
     my $plan   = $self->plan;
 
     # Find the change in the database.
-    my $to_id = $self->change_id_for_key( $key ) || hurl $ident => (
+    my $to_id =  $self->find_change_id(
+        ($pop ? (tag => 'HEAD') : ()), $self->_params_for_key($key)
+    ) || hurl $ident => (
         $plan->contains( $key ) ? __x(
             'Change "{change}" has not been deployed',
             change => $key,
@@ -410,7 +413,7 @@ sub _trim_to {
         change => $key,
     );
 
-    # Pope or shift changes till we find the change we want.
+    # Pop or shift changes till we find the change we want.
     if ($pop) {
         pop @{ $changes }   while $changes->[-1]->id ne $to_id;
     } else {
@@ -650,7 +653,7 @@ sub _params_for_key {
     my @off = ( offset => $offset );
     return ( @off, change => $cname, tag => $tag ) if $tag;
     return ( @off, change_id => $cname ) if $cname =~ /^[0-9a-f]{40}$/;
-    return ( @off, tag => '@' . $cname ) if $cname eq 'HEAD' || $cname eq 'ROOT';
+    return ( @off, tag => $cname ) if $cname eq 'HEAD' || $cname eq 'ROOT';
     return ( @off, change => $cname );
 }
 

t/engine.t

@@ -1766,7 +1766,7 @@ is $@->message, __x(
 is_deeply $engine->seen, [['change_id_for', {
     change_id => undef,
     change  => 'nonexistent',
-    tag     => undef,
+    tag     => 'HEAD',
     project => 'sql',
 }]], 'Should have called change_id_for() with change name';
 is_deeply +MockOutput->get_info, [], 'Nothing should have been output';
@@ -1782,9 +1782,9 @@ is $@->message, __x(
 is_deeply $engine->seen, [['change_id_for', {
     change_id => '8d77c5f588b60bc0f2efcda6369df5cb0177521d',
     change  => undef,
-    tag     => undef,
+    tag     => 'HEAD',
     project => 'sql',
-}]], 'Shoudl have called change_id_for() with change ID';
+}]], 'Should have called change_id_for() with change ID';
 is_deeply +MockOutput->get_info, [], 'Nothing should have been output';
 
 # Revert an undeployed change.
@@ -1820,7 +1820,7 @@ is_deeply $engine->seen, [
     [change_id_for => {
         change_id => $changes[0]->id,
         change => undef,
-        tag => undef,
+        tag => 'HEAD',
         project => 'sql',
     }],
     [ change_offset_from_id => [$changes[0]->id, 0] ],
@@ -2542,7 +2542,7 @@ is_deeply $engine->seen, [
         project => 'sql',
         tag => undef,
     } ]
-], 'It should have passed the change name to change_id_for';
+], 'It should have passed the change name and ROOT tag to change_id_for';
 
 # Should get an error when it's in the plan but not the database.
 throws_ok { $engine->_trim_to( 'yep', 'blah', [] ) } 'App::Sqitch::X',
@@ -2629,7 +2629,7 @@ is_deeply $engine->seen, [
         change => $key,
         change_id => undef,
         project => 'sql',
-        tag => undef,
+        tag => 'HEAD',
     } ],
     [ change_id_offset_from_id => [$changes[-1]->id, 0]],
 ], 'It should have passed change -1 ID to change_id_offset_from_id';
@@ -2647,7 +2647,7 @@ is_deeply $engine->seen, [
         change => $key,
         change_id => undef,
         project => 'sql',
-        tag => undef,
+        tag => 'HEAD',
     } ],
     [ change_id_offset_from_id => [$changes[-3]->id, 0]],
 ], 'It should have passed change -3 ID to change_id_offset_from_id';
@@ -2663,7 +2663,7 @@ is_deeply $engine->seen, [
         change => $key,
         change_id => undef,
         project => 'sql',
-        tag => undef,
+        tag => 'HEAD',
     } ],
     [ change_id_offset_from_id => [$changes[-3]->id, -1]],
 ], 'Should pass change -3 ID and offset -1 to change_id_offset_from_id';
@@ -2679,7 +2679,7 @@ is_deeply $engine->seen, [
         change => $key,
         change_id => undef,
         project => 'sql',
-        tag => undef,
+        tag => 'HEAD',
     } ],
     [ change_id_offset_from_id => [$changes[-3]->id, 1]],
 ], 'Should pass change -3 ID and offset 1 to change_id_offset_from_id';
@@ -2714,7 +2714,7 @@ is_deeply $engine->seen, [
         change => undef,
         change_id => undef,
         project => 'sql',
-        tag => '@HEAD',
+        tag => 'HEAD',
     } ],
     [ change_id_offset_from_id => [$changes[2]->id, 0]],
 ], 'Should pass tag @HEAD to change_id_for';
@@ -2749,7 +2749,7 @@ is_deeply $engine->seen, [
         change => undef,
         change_id => undef,
         project => 'sql',
-        tag => '@ROOT',
+        tag => 'ROOT',
     } ],
     [ change_id_offset_from_id => [$changes[2]->id, 0]],
 ], 'Should pass tag @ROOT to change_id_for';