feat: Allow schema metadata to be strongly typed

README.md

@@ -95,7 +95,7 @@ const parsedUser = await userSchema.validate(
   - [`Schema`](#schema)
     - [`Schema.clone(): Schema`](#schemaclone-schema)
     - [`Schema.label(label: string): Schema`](#schemalabellabel-string-schema)
-    - [`Schema.meta(metadata: object): Schema`](#schemametametadata-object-schema)
+    - [`Schema.meta(metadata: SchemaMetadata): Schema`](#schemametametadata-schemametadata-schema)
     - [`Schema.describe(options?: ResolveOptions): SchemaDescription`](#schemadescribeoptions-resolveoptions-schemadescription)
     - [`Schema.concat(schema: Schema): Schema`](#schemaconcatschema-schema-schema)
     - [`Schema.validate(value: any, options?: object): Promise<InferType<Schema>, ValidationError>`](#schemavalidatevalue-any-options-object-promiseinfertypeschema-validationerror)
@@ -631,10 +631,30 @@ Creates a deep copy of the schema. Clone is used internally to return a new sche
 
 Overrides the key name which is used in error messages.
 
-#### `Schema.meta(metadata: object): Schema`
+#### `Schema.meta(metadata: SchemaMetadata): Schema`
 
 Adds to a metadata object, useful for storing data with a schema, that doesn't belong
-the cast object itself.
+to the cast object itself.
+
+A custom `SchemaMetadata` interface can be defined through
+[merging](https://www.typescriptlang.org/docs/handbook/declaration-merging.html#merging-interfaces)
+with the `CustomSchemaMetadata` interface. Start by creating a `yup.d.ts` file
+in your package and creating your desired `CustomSchemaMetadata` interface:
+
+```ts
+// yup.d.ts
+import 'yup';
+
+declare module 'yup' {
+  // Define your desired `SchemaMetadata` interface by merging the
+  // `CustomSchemaMetadata` interface.
+  export interface CustomSchemaMetadata {
+    placeholderText?: string
+    tooltipText?: string
+    // …
+  }
+}
+```
 
 #### `Schema.describe(options?: ResolveOptions): SchemaDescription`
 

src/index.ts

@@ -27,6 +27,8 @@ import Schema, {
   SchemaLazyDescription,
   SchemaFieldDescription,
   SchemaDescription,
+  SchemaMetadata,
+  CustomSchemaMetadata,
 } from './schema';
 import type {
   InferType,
@@ -77,6 +79,8 @@ export type {
   SchemaLazyDescription,
   SchemaFieldDescription,
   SchemaDescription,
+  SchemaMetadata,
+  CustomSchemaMetadata,
   LocaleObject,
   ValidateOptions,
   DefaultThunk,

src/schema.ts

@@ -44,9 +44,17 @@ export type SchemaSpec<TDefault> = {
   strict?: boolean;
   recursive?: boolean;
   label?: string | undefined;
-  meta?: any;
+  meta?: SchemaMetadata;
 };
 
+export interface CustomSchemaMetadata {}
+
+// If `CustomSchemaMeta` isn't extended with any keys, we'll fall back to a
+// loose Record definition allowing free form usage.
+export type SchemaMetadata = keyof CustomSchemaMetadata extends never
+  ? Record<PropertyKey, any>
+  : CustomSchemaMetadata;
+
 export type SchemaOptions<TType, TDefault> = {
   type: string;
   spec?: Partial<SchemaSpec<TDefault>>;
@@ -111,7 +119,7 @@ export interface SchemaObjectDescription extends SchemaDescription {
 export interface SchemaLazyDescription {
   type: string;
   label?: string;
-  meta: object | undefined;
+  meta?: SchemaMetadata;
 }
 
 export type SchemaFieldDescription =
@@ -124,7 +132,7 @@ export type SchemaFieldDescription =
 export interface SchemaDescription {
   type: string;
   label?: string;
-  meta: object | undefined;
+  meta?: SchemaMetadata;
   oneOf: unknown[];
   notOneOf: unknown[];
   default?: unknown;
@@ -234,9 +242,9 @@ export default abstract class Schema<
     return next;
   }
 
-  meta(): Record<string, unknown> | undefined;
-  meta(obj: Record<string, unknown>): this;
-  meta(...args: [Record<string, unknown>?]) {
+  meta(): SchemaMetadata | undefined;
+  meta(obj: SchemaMetadata): this;
+  meta(...args: [SchemaMetadata?]) {
     if (args.length === 0) return this.spec.meta;
 
     let next = this.clone();