fix(v2): Fix MDX docs being considered as partials when siteDir match the _ prefix convention (#5199)

* Add _ to dogfood docs folder to cover against edge case

* Fix edge case with MDX partials when site / content dir contains a _ prefix

* add globUtils tests

* proper dogfooding folder re-organization, all content plugins being used

* refactor dogfooding folder + expose /tests page index

* fix page plugin ignoring options.routeBasePath

packages/docusaurus-utils/src/globUtils.ts

@@ -8,8 +8,8 @@
 // Globby/Micromatch are the 2 libs we use in Docusaurus consistently
 
 export {default as Globby} from 'globby';
-
 import Micromatch from 'micromatch'; // Note: Micromatch is used by Globby
+import path from 'path';
 
 // The default patterns we ignore when globbing
 // using _ prefix for exclusion by convention
@@ -33,3 +33,31 @@ export function createMatcher(patterns: string[]): Matcher {
   );
   return (str) => regexp.test(str);
 }
+
+// We use match patterns like '**/_*/**',
+// This function permits to help to:
+// Match /user/sebastien/website/docs/_partials/xyz.md
+// Ignore /user/_sebastien/website/docs/partials/xyz.md
+export function createAbsoluteFilePathMatcher(
+  patterns: string[],
+  rootFolders: string[],
+): Matcher {
+  const matcher = createMatcher(patterns);
+
+  function getRelativeFilePath(absoluteFilePath: string) {
+    const rootFolder = rootFolders.find((folderPath) =>
+      absoluteFilePath.startsWith(folderPath),
+    );
+    if (!rootFolder) {
+      throw new Error(
+        `createAbsoluteFilePathMatcher unexpected error, absoluteFilePath=${absoluteFilePath} was not contained in any of the root folders ${JSON.stringify(
+          rootFolders,
+        )}`,
+      );
+    }
+    return path.relative(rootFolder, absoluteFilePath);
+  }
+
+  return (absoluteFilePath: string) =>
+    matcher(getRelativeFilePath(absoluteFilePath));
+}