chore: improve expression types

Author: GerkinDev

lib/index.d.ts

@@ -26,7 +26,7 @@ declare namespace Joi {
 
     type BasicType = boolean | number | string | any[] | object | null;
 
-    type LanguageMessages = Record<string, string | Record<string, string>>;
+    type LanguageMessages = Record<string, string | Expression | Record<string, string | Expression>>;
 
     type PresenceMode = 'optional' | 'required' | 'forbidden';
 
@@ -641,6 +641,10 @@ declare namespace Joi {
         render?: boolean;
     }
 
+    interface ExpressionOptions extends ReferenceOptions {
+        functions: Record<string, (...args: unknown[]) => unknown>
+    }
+
     interface StringRegexOptions {
         /**
          * optional pattern name.
@@ -1987,6 +1991,8 @@ declare namespace Joi {
         toString(): string;
     }
 
+    interface Expression {}
+
     type ExtensionBoundSchema = Schema & SchemaInternals;
 
     interface RuleArgs {
@@ -2260,7 +2266,7 @@ declare namespace Joi {
         /**
          * Generates a dynamic expression using a template string.
          */
-        expression(template: string, options?: ReferenceOptions): any;
+        expression(template: string, options?: ExpressionOptions): Expression;
 
         /**
          * Creates a new Joi instance customized with the extension(s) you provide included.
@@ -2324,8 +2330,9 @@ declare namespace Joi {
 
         /**
          * Generates a dynamic expression using a template string.
+         * @see {@link Root.expression}
          */
-        x(template: string, options?: ReferenceOptions): any;
+        x(template: string, options?: ExpressionOptions): Expression;
 
         // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
         // Below are undocumented APIs. use at your own risk