WIP - add extractor, generate snippet_data

node_modules/regexp-tree/dist/optimizer/transforms/remove-empty-group-transform.js

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+/**
+ * The MIT License (MIT)
+ * Copyright (c) 2017-present Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
+ */
+
+'use strict';
+
+/**
+ * A regexp-tree plugin to remove non-capturing empty groups.
+ *
+ * /(?:)a/ -> /a/
+ * /a|(?:)/ -> /a|/
+ */
+
+module.exports = {
+  Group: function Group(path) {
+    var node = path.node,
+        parent = path.parent;
+
+    var childPath = path.getChild();
+
+    if (node.capturing || childPath) {
+      return;
+    }
+
+    if (parent.type === 'Repetition') {
+
+      path.getParent().replace(node);
+    } else if (parent.type !== 'RegExp') {
+
+      path.remove();
+    }
+  }
+};