Fix output type of nullable, nullish and optional #593

library/src/methods/fallback/fallback.ts

@@ -43,7 +43,7 @@ export type SchemaWithFallback<
  */
 export function fallback<
   const TSchema extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
-  TFallback extends Fallback<TSchema>,
+  const TFallback extends Fallback<TSchema>,
 >(
   schema: TSchema,
   fallback: TFallback

library/src/methods/fallback/fallbackAsync.ts

@@ -69,7 +69,7 @@ export function fallbackAsync<
   const TSchema extends
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
-  TFallback extends FallbackAsync<TSchema>,
+  const TFallback extends FallbackAsync<TSchema>,
 >(
   schema: TSchema,
   fallback: TFallback

library/src/schemas/nullable/index.ts

@@ -1,2 +1,3 @@
 export * from './nullable.ts';
 export * from './nullableAsync.ts';
+export * from './types.ts';

library/src/schemas/nullable/nullable.ts

@@ -4,12 +4,10 @@ import type {
   BaseSchema,
   Dataset,
   Default,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonNullable,
 } from '../../types/index.ts';
+import type { InferNullableOutput } from './types.ts';
 
 /**
  * Nullable schema type.
@@ -19,11 +17,7 @@ export interface NullableSchema<
   TDefault extends Default<TWrapped, null>,
 > extends BaseSchema<
     InferInput<TWrapped> | null,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | null
-      : // FIXME: For schemas that transform the input to `null`, this
-        // implementation may result in an incorrect output type
-        NonNullable<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferNullableOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -69,7 +63,7 @@ export function nullable<
  */
 export function nullable<
   const TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends Default<TWrapped, null>,
+  const TDefault extends Default<TWrapped, null>,
 >(wrapped: TWrapped, default_: TDefault): NullableSchema<TWrapped, TDefault>;
 
 export function nullable(

library/src/schemas/nullable/nullableAsync.ts

@@ -5,12 +5,10 @@ import type {
   BaseSchemaAsync,
   Dataset,
   DefaultAsync,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonNullable,
 } from '../../types/index.ts';
+import type { InferNullableOutput } from './types.ts';
 
 /**
  * Nullable schema async type.
@@ -22,11 +20,7 @@ export interface NullableSchemaAsync<
   TDefault extends DefaultAsync<TWrapped, null>,
 > extends BaseSchemaAsync<
     InferInput<TWrapped> | null,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | null
-      : // FIXME: For schemas that transform the input to `null`, this
-        // implementation may result in an incorrect output type
-        NonNullable<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferNullableOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -76,7 +70,7 @@ export function nullableAsync<
   const TWrapped extends
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends DefaultAsync<TWrapped, null>,
+  const TDefault extends DefaultAsync<TWrapped, null>,
 >(
   wrapped: TWrapped,
   default_: TDefault

library/src/schemas/nullable/types.ts

@@ -0,0 +1,23 @@
+import type {
+  BaseIssue,
+  BaseSchema,
+  BaseSchemaAsync,
+  DefaultAsync,
+  DefaultValue,
+  InferOutput,
+  NonNullable,
+} from '../../types/index.ts';
+
+/**
+ * Infer nullable output type.
+ */
+export type InferNullableOutput<
+  TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends DefaultAsync<TWrapped, undefined>,
+> = [TDefault] extends [never]
+  ? InferOutput<TWrapped> | null
+  : // FIXME: For schemas that transform the input to `undefined`, this
+    // implementation may result in an incorrect output type
+    NonNullable<InferOutput<TWrapped>> | Extract<DefaultValue<TDefault>, null>;

library/src/schemas/nullish/index.ts

@@ -1,2 +1,3 @@
 export * from './nullish.ts';
 export * from './nullishAsync.ts';
+export * from './types.ts';

library/src/schemas/nullish/nullish.ts

@@ -4,12 +4,10 @@ import type {
   BaseSchema,
   Dataset,
   Default,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonNullish,
 } from '../../types/index.ts';
+import type { InferNullishOutput } from './types.ts';
 
 /**
  * Nullish schema type.
@@ -19,11 +17,7 @@ export interface NullishSchema<
   TDefault extends Default<TWrapped, null | undefined>,
 > extends BaseSchema<
     InferInput<TWrapped> | null | undefined,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | null | undefined
-      : // FIXME: For schemas that transform the input to `null` or `undefined`,
-        // this implementation may result in an incorrect output type
-        NonNullish<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferNullishOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -69,7 +63,7 @@ export function nullish<
  */
 export function nullish<
   const TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends Default<TWrapped, null | undefined>,
+  const TDefault extends Default<TWrapped, null | undefined>,
 >(wrapped: TWrapped, default_: TDefault): NullishSchema<TWrapped, TDefault>;
 
 export function nullish(

library/src/schemas/nullish/nullishAsync.ts

@@ -5,12 +5,10 @@ import type {
   BaseSchemaAsync,
   Dataset,
   DefaultAsync,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonNullish,
 } from '../../types/index.ts';
+import type { InferNullishOutput } from './types.ts';
 
 /**
  * Nullish schema async type.
@@ -22,11 +20,7 @@ export interface NullishSchemaAsync<
   TDefault extends DefaultAsync<TWrapped, null | undefined>,
 > extends BaseSchemaAsync<
     InferInput<TWrapped> | null | undefined,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | null | undefined
-      : // FIXME: For schemas that transform the input to `null` or `undefined`,
-        // this implementation may result in an incorrect output type
-        NonNullish<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferNullishOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -76,7 +70,7 @@ export function nullishAsync<
   const TWrapped extends
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends DefaultAsync<TWrapped, null | undefined>,
+  const TDefault extends DefaultAsync<TWrapped, null | undefined>,
 >(
   wrapped: TWrapped,
   default_: TDefault

library/src/schemas/nullish/types.ts

@@ -0,0 +1,24 @@
+import type {
+  BaseIssue,
+  BaseSchema,
+  BaseSchemaAsync,
+  DefaultAsync,
+  DefaultValue,
+  InferOutput,
+  NonNullish,
+} from '../../types/index.ts';
+
+/**
+ * Infer nullish output type.
+ */
+export type InferNullishOutput<
+  TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends DefaultAsync<TWrapped, undefined>,
+> = [TDefault] extends [never]
+  ? InferOutput<TWrapped> | null | undefined
+  : // FIXME: For schemas that transform the input to `undefined`, this
+    // implementation may result in an incorrect output type
+    | NonNullish<InferOutput<TWrapped>>
+      | Extract<DefaultValue<TDefault>, null | undefined>;

library/src/schemas/optional/index.ts

@@ -1,2 +1,3 @@
 export * from './optional.ts';
 export * from './optionalAsync.ts';
+export * from './types.ts';

library/src/schemas/optional/optional.ts

@@ -4,12 +4,10 @@ import type {
   BaseSchema,
   Dataset,
   Default,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonOptional,
 } from '../../types/index.ts';
+import type { InferOptionalOutput } from './types.ts';
 
 /**
  * Optional schema type.
@@ -19,11 +17,7 @@ export interface OptionalSchema<
   TDefault extends Default<TWrapped, undefined>,
 > extends BaseSchema<
     InferInput<TWrapped> | undefined,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | undefined
-      : // FIXME: For schemas that transform the input to `undefined`, this
-        // implementation may result in an incorrect output type
-        NonOptional<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferOptionalOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -69,7 +63,7 @@ export function optional<
  */
 export function optional<
   const TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends Default<TWrapped, undefined>,
+  const TDefault extends Default<TWrapped, undefined>,
 >(wrapped: TWrapped, default_: TDefault): OptionalSchema<TWrapped, TDefault>;
 
 export function optional(

library/src/schemas/optional/optionalAsync.ts

@@ -5,12 +5,10 @@ import type {
   BaseSchemaAsync,
   Dataset,
   DefaultAsync,
-  DefaultValue,
   InferInput,
   InferIssue,
-  InferOutput,
-  NonOptional,
 } from '../../types/index.ts';
+import type { InferOptionalOutput } from './types.ts';
 
 /**
  * Optional schema async type.
@@ -22,11 +20,7 @@ export interface OptionalSchemaAsync<
   TDefault extends DefaultAsync<TWrapped, undefined>,
 > extends BaseSchemaAsync<
     InferInput<TWrapped> | undefined,
-    [TDefault] extends [never]
-      ? InferOutput<TWrapped> | undefined
-      : // FIXME: For schemas that transform the input to `undefined`, this
-        // implementation may result in an incorrect output type
-        NonOptional<InferOutput<TWrapped>> | DefaultValue<TDefault>,
+    InferOptionalOutput<TWrapped, TDefault>,
     InferIssue<TWrapped>
   > {
   /**
@@ -76,7 +70,7 @@ export function optionalAsync<
   const TWrapped extends
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
-  TDefault extends DefaultAsync<TWrapped, undefined>,
+  const TDefault extends DefaultAsync<TWrapped, undefined>,
 >(
   wrapped: TWrapped,
   default_: TDefault

library/src/schemas/optional/types.ts

@@ -0,0 +1,24 @@
+import type {
+  BaseIssue,
+  BaseSchema,
+  BaseSchemaAsync,
+  DefaultAsync,
+  DefaultValue,
+  InferOutput,
+  NonOptional,
+} from '../../types/index.ts';
+
+/**
+ * Infer optional output type.
+ */
+export type InferOptionalOutput<
+  TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends DefaultAsync<TWrapped, undefined>,
+> = [TDefault] extends [never]
+  ? InferOutput<TWrapped> | undefined
+  : // FIXME: For schemas that transform the input to `undefined`, this
+    // implementation may result in an incorrect output type
+    | NonOptional<InferOutput<TWrapped>>
+      | Extract<DefaultValue<TDefault>, undefined>;