refactor: unify how validateOptions is handled (#6961)

* refactor: unify how validateOptions is handled

* fix types

* fix again

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

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  JoiFrontMatter as Joi, // Custom instance for front matter
+  URISchema,
+  FrontMatterTagsSchema,
+  FrontMatterTOCHeadingLevels,
+  validateFrontMatter,
+} from '@docusaurus/utils-validation';
+import type {DocFrontMatter} from './types';
+
+// NOTE: we don't add any default value on purpose here
+// We don't want default values to magically appear in doc metadata and props
+// While the user did not provide those values explicitly
+// We use default values in code instead
+const DocFrontMatterSchema = Joi.object<DocFrontMatter>({
+  id: Joi.string(),
+  title: Joi.string().allow(''), // see https://github.com/facebook/docusaurus/issues/4591#issuecomment-822372398
+  hide_title: Joi.boolean(),
+  hide_table_of_contents: Joi.boolean(),
+  keywords: Joi.array().items(Joi.string().required()),
+  image: URISchema,
+  description: Joi.string().allow(''), // see https://github.com/facebook/docusaurus/issues/4591#issuecomment-822372398
+  slug: Joi.string(),
+  sidebar_label: Joi.string(),
+  sidebar_position: Joi.number(),
+  sidebar_class_name: Joi.string(),
+  sidebar_custom_props: Joi.object().unknown(),
+  displayed_sidebar: Joi.string().allow(null),
+  tags: FrontMatterTagsSchema,
+  pagination_label: Joi.string(),
+  custom_edit_url: URISchema.allow('', null),
+  parse_number_prefixes: Joi.boolean(),
+  pagination_next: Joi.string().allow(null),
+  pagination_prev: Joi.string().allow(null),
+  ...FrontMatterTOCHeadingLevels,
+}).unknown();
+
+export function validateDocFrontMatter(
+  frontMatter: Record<string, unknown>,
+): DocFrontMatter {
+  return validateFrontMatter(frontMatter, DocFrontMatterSchema);
+}