remove type-level error message from optional signature, closes #3290…

… (#3291)

.changeset/moody-maps-agree.md

@@ -0,0 +1,7 @@
+---
+"@effect/schema": patch
+---
+
+remove type-level error message from `optional` signature, closes #3290
+
+This fix eliminates the type-level error message from the `optional` function signature, which was causing issues in generic contexts.

packages/schema/dtslint/Schema.ts

@@ -523,9 +523,6 @@ S.Struct({ a: S.String.pipe(S.optional({ exact: true })) })
 // optional - Errors
 // ---------------------------------------------
 
-// @ts-expect-error
-S.Boolean.pipe(S.optional)
-
 // @ts-expect-error
 S.optional(S.String, { as: "Option", default: () => "" })
 
@@ -559,6 +556,19 @@ S.optional(S.String, { as: null })
 // @ts-expect-error
 S.optional(S.String, { default: null })
 
+// ---------------------------------------------
+// optional() used in a generic context
+// ---------------------------------------------
+
+type TypeWithValue<Value extends S.Schema.Any> = { value: S.optionalWithOptions<Value, { nullable: true }> }
+
+const makeTypeWithValue = <Value extends S.Schema.Any>(value: Value): TypeWithValue<Value> => ({
+  value: S.optional(value, { nullable: true })
+})
+
+// $ExpectType TypeWithValue<typeof String$>
+makeTypeWithValue(S.String)
+
 // ---------------------------------------------
 // optional()
 // ---------------------------------------------

packages/schema/src/Schema.ts

@@ -2243,13 +2243,10 @@ export const optional: {
     options?: Options
   ): (self: S) => [undefined] extends [Options] ? optional<S> : optionalWithOptions<S, Options>
   <S extends Schema.All, Options extends OptionalOptions<Schema.Type<S>>>(
-    self: Schema.All extends S ? "you can't apply optional implicitly, use optional() instead" : S,
+    self: S,
     options?: Options
   ): [undefined] extends [Options] ? optional<S> : optionalWithOptions<S, Options>
 } = dual((args) => isSchema(args[0]), (from, options) => {
-  // Note: `Schema.All extends S ? "you can't...` is used to prevent the case where `optional` is implicitly applied.
-  // For example: `S.String.pipe(S.optional)` would result in `S.String` being inferred as `Schema.All`,
-  // which is not the intended behavior. This is mostly an aesthetic consideration, so if it causes issues, we can remove it.
   return new PropertySignatureWithFromImpl(optionalPropertySignatureAST(from, options), from)
 })