fix(v2): fix multi-instance mdx loaders not sandboxed correctly (#3970)

* another attempt to fix the multi-instance conflicts

* try to fix windows build

* cleanup + improve comment

packages/docusaurus-plugin-content-blog/src/index.ts

@@ -15,6 +15,7 @@ import {
   getPluginI18nPath,
   reportMessage,
   posixPath,
+  addTrailingPathSeparator,
 } from '@docusaurus/utils';
 import {
   STATIC_DIR_NAME,
@@ -436,7 +437,9 @@ export default function pluginContentBlog(
           rules: [
             {
               test: /(\.mdx?)$/,
-              include: getContentPathList(contentPaths),
+              include: getContentPathList(contentPaths)
+                // Trailing slash is important, see https://github.com/facebook/docusaurus/pull/3970
+                .map(addTrailingPathSeparator),
               use: [
                 getCacheLoader(isServer),
                 getBabelLoader(isServer),

packages/docusaurus-plugin-content-docs/src/index.ts

@@ -17,6 +17,7 @@ import {
   aliasedSitePath,
   reportMessage,
   posixPath,
+  addTrailingPathSeparator,
 } from '@docusaurus/utils';
 import {LoadContext, Plugin, RouteConfig} from '@docusaurus/types';
 
@@ -345,7 +346,9 @@ export default function pluginContentDocs(
       function createMDXLoaderRule(): RuleSetRule {
         return {
           test: /(\.mdx?)$/,
-          include: flatten(versionsMetadata.map(getDocsDirPaths)),
+          include: flatten(versionsMetadata.map(getDocsDirPaths))
+            // Trailing slash is important, see https://github.com/facebook/docusaurus/pull/3970
+            .map(addTrailingPathSeparator),
           use: compact([
             getCacheLoader(isServer),
             getBabelLoader(isServer),

packages/docusaurus-plugin-content-pages/src/index.ts

@@ -17,6 +17,7 @@ import {
   docuHash,
   getPluginI18nPath,
   getFolderContainingFile,
+  addTrailingPathSeparator,
 } from '@docusaurus/utils';
 import {
   LoadContext,
@@ -210,7 +211,9 @@ export default function pluginContentPages(
           rules: [
             {
               test: /(\.mdx?)$/,
-              include: getContentPathList(contentPaths),
+              include: getContentPathList(contentPaths)
+                // Trailing slash is important, see https://github.com/facebook/docusaurus/pull/3970
+                .map(addTrailingPathSeparator),
               use: [
                 getCacheLoader(isServer),
                 getBabelLoader(isServer),

packages/docusaurus-utils/src/index.ts

@@ -414,6 +414,9 @@ export function addLeadingSlash(str: string): string {
 export function addTrailingSlash(str: string): string {
   return str.endsWith('/') ? str : `${str}/`;
 }
+export function addTrailingPathSeparator(str: string): string {
+  return str.endsWith(path.sep) ? str : `${str}${path.sep}`;
+}
 
 export function removeTrailingSlash(str: string): string {
   return removeSuffix(str, '/');