Address new TypeScript warnings in core files, improve type definitions.

lib/markdownlint.d.mts

@@ -26,39 +26,38 @@ export function lintSync(options: Options | null): LintResults;
  * @param {Configuration} config Configuration object.
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[] | undefined} parsers Parsing function(s).
- * @param {Object} fs File system implementation.
+ * @param {FsLike} fs File system implementation.
  * @returns {Promise<Configuration>} Configuration object.
  */
-export function extendConfigPromise(config: Configuration, file: string, parsers: ConfigurationParser[] | undefined, fs: any): Promise<Configuration>;
+export function extendConfigPromise(config: Configuration, file: string, parsers: ConfigurationParser[] | undefined, fs: FsLike): Promise<Configuration>;
 /**
  * Read specified configuration file.
  *
  * @param {string} file Configuration file name.
- * @param {ConfigurationParser[] | ReadConfigCallback} [parsers] Parsing
- * function(s).
- * @param {Object} [fs] File system implementation.
+ * @param {ConfigurationParser[] | ReadConfigCallback} [parsers] Parsing function(s).
+ * @param {FsLike | ReadConfigCallback} [fs] File system implementation.
  * @param {ReadConfigCallback} [callback] Callback (err, result) function.
  * @returns {void}
  */
-export function readConfigAsync(file: string, parsers?: ConfigurationParser[] | ReadConfigCallback, fs?: any, callback?: ReadConfigCallback): void;
+export function readConfigAsync(file: string, parsers?: ConfigurationParser[] | ReadConfigCallback, fs?: FsLike | ReadConfigCallback, callback?: ReadConfigCallback): void;
 /**
  * Read specified configuration file.
  *
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[]} [parsers] Parsing function(s).
- * @param {Object} [fs] File system implementation.
+ * @param {FsLike} [fs] File system implementation.
  * @returns {Promise<Configuration>} Configuration object.
  */
-export function readConfigPromise(file: string, parsers?: ConfigurationParser[], fs?: any): Promise<Configuration>;
+export function readConfigPromise(file: string, parsers?: ConfigurationParser[], fs?: FsLike): Promise<Configuration>;
 /**
  * Read specified configuration file.
  *
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[]} [parsers] Parsing function(s).
- * @param {Object} [fs] File system implementation.
+ * @param {FsLike} [fs] File system implementation.
  * @returns {Configuration} Configuration object.
  */
-export function readConfigSync(file: string, parsers?: ConfigurationParser[], fs?: any): Configuration;
+export function readConfigSync(file: string, parsers?: ConfigurationParser[], fs?: FsLike): Configuration;
 /**
  * Applies the specified fix to a Markdown content line.
  *
@@ -82,6 +81,19 @@ export function applyFixes(input: string, errors: LintError[]): string;
  * @returns {string} SemVer string.
  */
 export function getVersion(): string;
+/**
+ * Result object for removeFrontMatter.
+ */
+export type RemoveFrontMatterResult = {
+    /**
+     * Markdown content.
+     */
+    content: string;
+    /**
+     * Front matter lines.
+     */
+    frontMatterLines: string[];
+};
 /**
  * Result object for getEffectiveConfig.
  */
@@ -120,6 +132,27 @@ export type EnabledRulesPerLineNumberResult = {
      */
     rulesSeverity: Map<string, "error" | "warning">;
 };
+/**
+ * Node fs instance (or compatible object).
+ */
+export type FsLike = {
+    /**
+     * access method.
+     */
+    access: (path: string, callback: (err: Error) => void) => void;
+    /**
+     * accessSync method.
+     */
+    accessSync: (path: string) => void;
+    /**
+     * readFile method.
+     */
+    readFile: (path: string, encoding: string, callback: (err: Error, data: string) => void) => void;
+    /**
+     * readFileSync method.
+     */
+    readFileSync: (path: string, encoding: string) => string;
+};
 /**
  * Function to implement rule logic.
  */
@@ -418,7 +451,7 @@ export type Options = {
     /**
      * File system implementation.
      */
-    fs?: any;
+    fs?: FsLike;
     /**
      * True to catch exceptions.
      */
@@ -467,15 +500,15 @@ export type LintError = {
     /**
      * Link to more information.
      */
-    ruleInformation: string;
+    ruleInformation: string | null;
     /**
      * Detail about the error.
      */
-    errorDetail: string;
+    errorDetail: string | null;
     /**
      * Context for the error.
      */
-    errorContext: string;
+    errorContext: string | null;
     /**
      * Column number (1-based) and length.
      */