Don't die when default target plan file doesn't exist.

When parsing arguments, that is. Particularly important when the default
target and/or default plan file (sqitch.plan) doesn't exist. Resolves #324.

Changes

@@ -32,6 +32,8 @@ Revision history for Perl extension App::Sqitch
        that follows them (#312).
      - The `verify` command now looks for the most recent variant of a `--to`
        change if it's not tag-qualified.
+     - Sqitch no longer returns an error when specifying a target name to
+       commands when the default target's plan file does not exist (#324).
 
 0.9995 2016-07-27T09:23:55Z
      - Taught the `add` command not to ignore the `--change` option.

lib/App/Sqitch/Command.pm

@@ -220,7 +220,7 @@ sub parse_args {
 
     my %engines = map { $_ => 1 } ENGINES;
     for my $arg (@{ $p{args} }) {
-        if ( !$p{no_changes} && $target && $target->plan->contains($arg) ) {
+        if ( !$p{no_changes} && $target && -e $target->plan_file && $target->plan->contains($arg) ) {
             # A change.
             push @{ $rec{changes} } => $arg;
         } elsif ($config->get( key => "target.$arg.uri") || URI->new($arg)->isa('URI::db')) {

t/command.t

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 use 5.010;
 use utf8;
-use Test::More tests => 165;
+use Test::More tests => 166;
 #use Test::More 'no_plan';
 use Test::NoWarnings;
 use List::Util qw(first);
@@ -424,6 +424,12 @@ ARGS: {
 
     is_deeply $parsem->(args => ['sqlite']), [['devdb'], []],
         'Should resolve engine "sqlite" file to its target';
+
+    # Make sure we don't get an error when the default target has no plan file.
+    my $mock_target = Test::MockModule->new('App::Sqitch::Target');
+    $mock_target->mock(plan_file => file 'no-such-file.txt');
+    is_deeply $parsem->( args => ['devdb'] ),  [['devdb'], []],
+        'Should recognize target when default target has no plan file';
 }
 
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