Have init die on invalid project file.

If the project file exists already, and is either not a file, not a Sqitch
plan file, or defined for a different project, then throw an error so the user
has some idea what to do next. Closes #214.

Changes

@@ -38,6 +38,9 @@ Revision history for Perl extension App::Sqitch
      - Fixed the formatting of change notes so that a space preceeds the `#`
        character whether the note was added by the `--note` option or via an
        editor.
+     - The `init` command now throws an error when the plan file already
+       exists and is invalid or defined for a different project. Thanks to
+       Gabriel Potkány for the suggestion (Issue #214).
 
 0.999  2015-02-12T19:43:45Z
      - Improved MySQL missing table error detection by relying on error codes

lib/App/Sqitch/Command/init.pm

@@ -93,7 +93,33 @@ sub write_plan {
     my ( $self, $project ) = @_;
     my $target = $self->default_target;
     my $file   = $target->plan_file;
-    return $self if -f $file;
+
+    if (-e $file) {
+        hurl init => __x(
+            'Cannot initialize because {file} already exists and is not a file',
+            file => $file,
+        ) unless -f $file;
+
+        # Try to load the plan file.
+        my $plan = App::Sqitch::Plan->new(
+            sqitch => $self->sqitch,
+            file   => $file,
+            target => $self->default_target,
+        );
+        my $file_proj = try { $plan->project } or hurl init => __x(
+            'Cannot initialize because {file} already exists and is not a valid plan file',
+            file => $file,
+        );
+
+        # Bail if this plan file looks like it's for a different project.
+        hurl init => __x(
+            'Cannot initialize because project "{project}" already initialized in {file}',
+            project => $plan->project,
+            file    => $file,
+        ) if $plan->project ne $project;
+        return $self;
+    }
+
     $self->_mkdir( $file->dir ) unless -d $file->dir;
 
     my $fh = $file->open('>:utf8_strict') or hurl init => __x(

t/init.t

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 use 5.010;
 use utf8;
-use Test::More tests => 159;
+use Test::More tests => 167;
 #use Test::More 'no_plan';
 use App::Sqitch;
 use Locale::TextDomain qw(App-Sqitch);
@@ -434,13 +434,37 @@ file_contents_is $plan_file,
     '%project=nada' . "\n\n",
  'The contents should be correct';
 
-# Write more to the plan.
+# Make sure we don't overwrite the file when initializing again.
+ok $init->write_plan( 'nada' ), 'Write the plan file again';
+file_exists_ok $plan_file, 'Plan file should still exist';
+file_contents_is $plan_file,
+    '%syntax-version=' . App::Sqitch::Plan::SYNTAX_VERSION() . "\n" .
+    '%project=nada' . "\n\n",
+ 'The contents should be identical';
+
+# Make sure we get an error trying to initalize a different plan.
+throws_ok { $init->write_plan( 'oopsie' ) } 'App::Sqitch::X',
+    'Should get an error initialing a different project';
+is $@->ident, 'init', 'Initialization error ident should be "init"';
+is $@->message, __x(
+    'Cannot initialize because project "{project}" already initialized in {file}',
+    project => 'nada',
+    file    => $plan_file,
+), 'Initialzation error message should be correct';
+
+# Write a different file.
 my $fh = $plan_file->open('>:utf8_strict') or die "Cannot open $plan_file: $!\n";
 $fh->say('# testing 1, 2, 3');
 $fh->close;
 
 # Try writing again.
-ok $init->write_plan( 'foofoo' ), 'Write the plan file again';
+throws_ok { $init->write_plan( 'foofoo' ) } 'App::Sqitch::X',
+    'Should get an error initialzing a non-plan file';
+is $@->ident, 'init', 'Non-plan file error ident should be "init"';
+is $@->message, __x(
+    'Cannot initialize because {file} already exists and is not a valid plan file',
+    file    => $plan_file,
+), 'Non-plan file error message should be correct';
 file_contents_like $plan_file, qr/testing 1, 2, 3/,
     'The file should not be overwritten';