fix(removeComments): make preserving comments a param (#1812)

Converts the hard-coded exception to a param so users can override this
behavior to preserve custom patterns or drop the logic altogether.

plugins/plugins-types.ts

@@ -119,7 +119,9 @@ type DefaultPlugins = {
 
   moveElemsAttrsToGroup: void;
   moveGroupAttrsToElems: void;
-  removeComments: void;
+  removeComments: {
+    preservePatterns: Array<RegExp|string> | false
+  };
   removeDesc: {
     removeAny?: boolean;
   };

plugins/removeComments.js

@@ -5,6 +5,12 @@ const { detachNodeFromParent } = require('../lib/xast.js');
 exports.name = 'removeComments';
 exports.description = 'removes comments';
 
+/**
+ * If a comment matches one of the following patterns, it will be
+ * preserved by default. Particularly for copyright/license information.
+ */
+const DEFAULT_PRESERVE_PATTERNS = [/^!/];
+
 /**
  * Remove comments.
  *
@@ -16,13 +22,29 @@ exports.description = 'removes comments';
  *
  * @type {import('./plugins-types').Plugin<'removeComments'>}
  */
-exports.fn = () => {
+exports.fn = (_root, params) => {
+  const { preservePatterns = DEFAULT_PRESERVE_PATTERNS } = params;
+
   return {
     comment: {
       enter: (node, parentNode) => {
-        if (node.value.charAt(0) !== '!') {
-          detachNodeFromParent(node, parentNode);
+        if (preservePatterns) {
+          if (!Array.isArray(preservePatterns)) {
+            throw Error(
+              `Expected array in removeComments preservePatterns parameter but received ${preservePatterns}`
+            );
+          }
+
+          const matches = preservePatterns.some((pattern) => {
+            return new RegExp(pattern).test(node.value);
+          });
+
+          if (matches) {
+            return;
+          }
         }
+
+        detachNodeFromParent(node, parentNode);
       },
     },
   };