Apply suggestions from code review

Co-authored-by: Brad Zacher <brad.zacher@gmail.com>

docs/architecture/Parser.mdx

@@ -42,7 +42,7 @@ interface ParserOptions {
   lib?: string[];
   moduleResolver?: string;
   program?: import('typescript').Program;
-  project?: string | string[] | true;
+  project?: string[] | true;
   projectFolderIgnoreList?: string[];
   tsconfigRootDir?: string;
   warnOnUnsupportedTypeScriptVersion?: boolean;
@@ -192,7 +192,7 @@ This option allows you to provide a path to your project's `tsconfig.json`. **Th
 
 - If `true`, each source file's parse will find the nearest `tsconfig.json` file to that source file.
 
-  - This is done by checking that source file's directory for a `tsconfig.json`, then the parent's directory for a `tsconfig.json`, and so on - until one is found or the current working directory is passed.
+  - This is done by checking that source file's directory tree for the nearest `tsconfig.json`.
 
 - If you use project references, TypeScript will not automatically use project references to resolve files. This means that you will have to add each referenced tsconfig to the `project` field either separately, or via a glob.
 

docs/linting/Typed_Linting.md

@@ -42,15 +42,15 @@ You may see new rules reporting errors based on type information!
 The `parserOptions.project` option can be turned on with either:
 
 - `true`: to always use `tsconfig.json`s nearest to source files
-- `string | string[]`: any number of glob paths to match TSConfig files relative to the
+- `string[]`: any number of glob paths to match TSConfig files relative to the
 
 For example, if you use a specific `tsconfig.eslint.json` for linting, you'd specify:
 
 ```js title=".eslintrc.js"
 module.exports = {
   // ...
   parserOptions: {
-    project: './tsconfig.eslint.json',
+    project: ['./tsconfig.eslint.json'],
   },
   // ...
 };

packages/typescript-estree/src/parseSettings/getProjectConfigFiles.ts

@@ -6,7 +6,7 @@ import type { ParseSettings } from '.';
 
 const log = debug('typescript-eslint:typescript-estree:getProjectConfigFiles');
 
-const tsconfigMatchCache = new Map<string, string | undefined>();
+const TSCONFIG_MATCH_CACHE = new Map<string, string | undefined>();
 
 /**
  * @remarks Only use this for tests!
@@ -29,7 +29,7 @@ export function getProjectConfigFiles(
   project: string | string[] | true | undefined,
 ): string | string[] | undefined {
   if (project !== true) {
-    return project;
+    return Array.isArray(project) ? project : [project];
   }
 
   log('Looking for tsconfig.json at or above file: %s', parseSettings.filePath);