feat(v2): absolute slugs and slug resolution system (#3084)

* rework slug to allow absolute slugs and slug resolution

* add slug metadata tests

* refactor docs metadata test + fix slug bugs

* fix tests

* fix docs tests failing due to randomness + update snapshot

* add test for addLeadingSlash

packages/docusaurus-utils/src/__tests__/index.test.ts

@@ -25,6 +25,7 @@ import {
   removeSuffix,
   removePrefix,
   getFilePathForRoutePath,
+  addLeadingSlash,
 } from '../index';
 
 describe('load utils', () => {
@@ -412,6 +413,15 @@ describe('addTrailingSlash', () => {
   });
 });
 
+describe('addLeadingSlash', () => {
+  test('should no-op', () => {
+    expect(addLeadingSlash('/abc')).toEqual('/abc');
+  });
+  test('should add /', () => {
+    expect(addLeadingSlash('abc')).toEqual('/abc');
+  });
+});
+
 describe('removeTrailingSlash', () => {
   test('should no-op', () => {
     expect(removeTrailingSlash('/abcd')).toEqual('/abcd');

packages/docusaurus-utils/src/index.ts

@@ -14,6 +14,9 @@ import escapeStringRegexp from 'escape-string-regexp';
 import fs from 'fs-extra';
 import {URL} from 'url';
 
+// @ts-expect-error: no typedefs :s
+import resolvePathnameUnsafe from 'resolve-pathname';
+
 const fileHash = new Map();
 export async function generate(
   generatedFilesDir: string,
@@ -361,12 +364,20 @@ export function isValidPathname(str: string): boolean {
     return false;
   }
   try {
+    // weird, but is there a better way?
     return new URL(str, 'https://domain.com').pathname === str;
   } catch (e) {
     return false;
   }
 }
 
+// resolve pathname and fail fast if resolution fails
+export function resolvePathname(to: string, from?: string) {
+  return resolvePathnameUnsafe(to, from);
+}
+export function addLeadingSlash(str: string): string {
+  return str.startsWith('/') ? str : `/${str}`;
+}
 export function addTrailingSlash(str: string): string {
   return str.endsWith('/') ? str : `${str}/`;
 }