fix(validation): allow string opts to md plugins

Remark and Rehype plugins allow having options as a non-object type,
such as a string.

For instance, the official MDX docs even have an example of this:
See https://mdxjs.com/docs/extending-mdx/#using-plugins

The official plugin `remarkjs/remark-frontmatter` allows passing
a string, e.g. `"toml"` as the options arg, instead of an object.

packages/docusaurus-utils-validation/src/__tests__/__snapshots__/validationSchemas.test.ts.snap

@@ -32,8 +32,6 @@ exports[`validation schemas rehypePluginsSchema: for value=[[]] 1`] = `"\\"[0]\\
 
 exports[`validation schemas rehypePluginsSchema: for value=[[null,null]] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
 
-exports[`validation schemas rehypePluginsSchema: for value=[[null,true]] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
-
 exports[`validation schemas rehypePluginsSchema: for value=[3] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
 
 exports[`validation schemas rehypePluginsSchema: for value=[false] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
@@ -50,8 +48,6 @@ exports[`validation schemas remarkPluginsSchema: for value=[[]] 1`] = `"\\"[0]\\
 
 exports[`validation schemas remarkPluginsSchema: for value=[[null,null]] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
 
-exports[`validation schemas remarkPluginsSchema: for value=[[null,true]] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
-
 exports[`validation schemas remarkPluginsSchema: for value=[3] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;
 
 exports[`validation schemas remarkPluginsSchema: for value=[false] 1`] = `"\\"[0]\\" does not match any of the allowed types"`;

packages/docusaurus-utils-validation/src/__tests__/validationSchemas.test.ts

@@ -46,6 +46,10 @@ function testMarkdownPluginSchemas(schema: Joi.Schema) {
   testOK([() => {}]);
   testOK([[() => {}, {attr: 'val'}]]);
   testOK([[() => {}, {attr: 'val'}], () => {}, [() => {}, {attr: 'val'}]]);
+  // cSpell:ignore remarkjs
+  // official `remarkjs/remark-frontmatter` plugin accepts string options
+  testOK([[() => {}, 'string-option']]);
+  testOK([[() => {}, true]]);
 
   testFail(null);
   testFail(false);
@@ -55,7 +59,6 @@ function testMarkdownPluginSchemas(schema: Joi.Schema) {
   testFail([3]);
   testFail([[]]);
   testFail([[() => {}, undefined]]);
-  testFail([[() => {}, true]]);
 }
 
 describe('validation schemas', () => {

packages/docusaurus-utils-validation/src/validationSchemas.ts

@@ -19,7 +19,7 @@ export const PluginIdSchema = Joi.string()
 
 const MarkdownPluginsSchema = Joi.array()
   .items(
-    Joi.array().ordered(Joi.function().required(), Joi.object().required()),
+    Joi.array().ordered(Joi.function().required(), Joi.any().required()),
     Joi.function(),
     Joi.object(),
   )