ENH Skip repositories we've already tagged

If an error occurs when cow has already tagged 15 repos, we want to be
able to rerun the release command and skip anything we've already
tagged.

src/Model/Modules/Library.php

@@ -286,6 +286,20 @@ public function getTags()
         return $this->tags;
     }
 
+    /**
+     * Check if a tag exists in the repository
+     */
+    public function hasTag(string $tag): bool
+    {
+        $repo = $this->getRepository();
+        if ($this->getProject()->getFetchTags()) {
+            // Fetch remote tags from origin first
+            $repo->run('fetch', ['--tags']);
+        }
+
+        return (bool) $repo->run('tag', ['--list', $tag]);
+    }
+
     /**
      * Tag this module
      *

src/Steps/Release/PublishRelease.php

@@ -118,6 +118,11 @@ protected function releaseLibrary(
             die();
         }
 
+        if ($this->hasTag($releasePlanNode)) {
+            $this->log($output, "Library <info>{$name}</info> has already been released. <comment>Skipping.</comment>");
+            return;
+        }
+
         $versionName = $releasePlanNode->getVersion()->getValue();
         $this->log($output, "Releasing library <info>{$name}</info> at version <info>{$versionName}</info>");
 
@@ -163,6 +168,15 @@ protected function publishTag(OutputInterface $output, LibraryRelease $releasePl
         $this->log($output, 'Tagging complete');
     }
 
+    /**
+     * Check if this release node already has the tag we're going to release
+     */
+    protected function hasTag(LibraryRelease $releasePlan): bool
+    {
+        $library = $releasePlan->getLibrary();
+        $tag = $releasePlan->getVersion()->getValue();
+        return $library->hasTag($tag);
+    }
 
     /**
      * Update github release notes via github API