fix: never add trailing slashes to error pages

Author: openscript

src/utils/path.test.ts

@@ -77,9 +77,11 @@ describe('handleTrailingSlash', () => {
     expect(expectation).toBe('https://example.com/');
   });
 
-  it('should never add trailing slashes to paths with file extensions', () => {
-    const expectation = handleTrailingSlash('404.html', 'always');
+  it('should never add trailing slashes to error pages', () => {
+    let expectation = handleTrailingSlash('404.html', 'always');
     expect(expectation).toBe('404.html');
+    expectation = handleTrailingSlash('https://example.com/403.html/403.html', 'always');
+    expect(expectation).toBe('https://example.com/403.html/403.html');
   });
 });
 

src/utils/path.ts

@@ -1,8 +1,10 @@
 import { posix as nodePath } from 'path';
 import { PluginOptions } from 'gatsby';
 
+const ERROR_PAGE_PATH_PATTERN = /[0-9]{3}\.([0-9a-z]+)(?:[?#]|$)/gim;
+
 export const handleTrailingSlash = (path: string, trailingSlashOption: PluginOptions['trailingSlash'] = 'always') => {
-  if (path === '/' || path.length < 1) {
+  if (path === '/' || path.length < 1 || path.match(ERROR_PAGE_PATH_PATTERN)) {
     return path;
   }