add never handling to struct API, closes #242 (#245)

Effect-TS · Apr 18, 2023 · 6a7d7be · 6a7d7be
1 parent 0ce16a9
commit 6a7d7be
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diff --git a/.changeset/nasty-vans-tan.md b/.changeset/nasty-vans-tan.md
@@ -0,0 +1,5 @@
+---
+"@effect/schema": patch
+---
+
+add `never` handling to struct API
diff --git a/docs/modules/Schema.ts.md b/docs/modules/Schema.ts.md
@@ -40,6 +40,8 @@ Added in v1.0.0
   - [nonNegativeBigint](#nonnegativebigint)
   - [nonPositiveBigint](#nonpositivebigint)
   - [positiveBigint](#positivebigint)
+- [boolean](#boolean)
+  - [not](#not)
 - [combinators](#combinators)
   - [annotations](#annotations-1)
   - [array](#array-1)
@@ -139,7 +141,7 @@ Added in v1.0.0
 - [primitives](#primitives)
   - [any](#any)
   - [bigint](#bigint-1)
-  - [boolean](#boolean)
+  - [boolean](#boolean-1)
   - [never](#never)
   - [null](#null)
   - [number](#number-1)
@@ -519,6 +521,20 @@ export declare const positiveBigint: <A extends bigint>(
 
 Added in v1.0.0
 
+# boolean
+
+## not
+
+Negates a boolean value
+
+**Signature**
+
+```ts
+export declare const not: <I>(self: Schema<I, boolean>) => Schema<I, boolean>
+```
+
+Added in v1.0.0
+
 # combinators
 
 ## annotations
@@ -930,7 +946,13 @@ Added in v1.0.0
 
 ```ts
 export declare const struct: <
-  Fields extends Record<string | number | symbol, Schema<any, any> | PropertySignature<any, any, boolean>>
+  Fields extends Record<
+    string | number | symbol,
+    | Schema<any, any>
+    | Schema<never, never>
+    | PropertySignature<any, any, boolean>
+    | PropertySignature<never, never, boolean>
+  >
 >(
   fields: Fields
 ) => Schema<
@@ -2299,7 +2321,11 @@ Added in v1.0.0
 
 ```ts
 export type OptionalKeys<Fields, ToIsOptional extends boolean> = {
-  [K in keyof Fields]: Fields[K] extends PropertySignature<any, any, ToIsOptional> ? K : never
+  [K in keyof Fields]: Fields[K] extends
+    | PropertySignature<any, any, ToIsOptional>
+    | PropertySignature<never, never, ToIsOptional>
+    ? K
+    : never
 }[keyof Fields]
 ```
 
@@ -2310,7 +2336,7 @@ Added in v1.0.0
 **Signature**
 
 ```ts
-export interface PropertySignature<From, To = From, ToIsOptional extends boolean = true> {
+export interface PropertySignature<From, To = From, ToIsOptional extends boolean = boolean> {
   readonly From: (_: From) => From
   readonly To: (_: To) => To
   readonly ToIsOptional: ToIsOptional

diff --git a/dtslint/ts4.9/Schema.ts b/dtslint/ts4.9/Schema.ts
@@ -234,6 +234,9 @@ export type MyModelFrom = S.From<typeof MyModel>
 // $ExpectType { readonly a: string; readonly b: number; }
 export type MyModelTo = S.To<typeof MyModel>
 
+// $ExpectType Schema<{ readonly a: never; }, { readonly a: never; }>
+S.struct({ a: S.never })
+
 // ---------------------------------------------
 // optional
 // ---------------------------------------------
@@ -248,6 +251,9 @@ S.struct({ a: S.string, b: S.number, c: S.optional(NumberFromString) });
 // $ExpectType Schema<{ readonly a?: string; }, { readonly a?: string; }>
 S.struct({ a: pipe(S.string, S.optional) })
 
+// $ExpectType Schema<{ readonly a?: never; }, { readonly a?: never; }>
+ S.struct({ a: S.optional(S.never) })
+
 // ---------------------------------------------
 // optional.withDefault
 // ---------------------------------------------

diff --git a/src/Schema.ts b/src/Schema.ts
@@ -461,7 +461,7 @@ export type PropertySignatureId = typeof PropertySignatureId
 /**
  * @since 1.0.0
  */
-export interface PropertySignature<From, To = From, ToIsOptional extends boolean = true> {
+export interface PropertySignature<From, To = From, ToIsOptional extends boolean = boolean> {
   readonly From: (_: From) => From
   readonly To: (_: To) => To
   readonly ToIsOptional: ToIsOptional
@@ -504,7 +504,8 @@ optional.withDefault = dual(2, (schema, value) => _optional(schema, { to: "defau
  * @since 1.0.0
  */
 export type OptionalKeys<Fields, ToIsOptional extends boolean> = {
-  [K in keyof Fields]: Fields[K] extends PropertySignature<any, any, ToIsOptional> ? K
+  [K in keyof Fields]: Fields[K] extends
+    PropertySignature<any, any, ToIsOptional> | PropertySignature<never, never, ToIsOptional> ? K
     : never
 }[keyof Fields]
 
@@ -513,7 +514,13 @@ export type OptionalKeys<Fields, ToIsOptional extends boolean> = {
  * @since 1.0.0
  */
 export const struct = <
-  Fields extends Record<PropertyKey, Schema<any> | PropertySignature<any, any, boolean>>
+  Fields extends Record<
+    PropertyKey,
+    | Schema<any>
+    | Schema<never>
+    | PropertySignature<any>
+    | PropertySignature<never>
+  >
 >(
   fields: Fields
 ): Schema<

diff --git a/test/optional.ts b/test/optional.ts
@@ -25,6 +25,12 @@ describe.concurrent("optional", () => {
     await Util.expectEncodeSuccess(schema, { a: O.none() }, {})
   })
 
+  it("never", async () => {
+    const schema = S.struct({ a: S.optional(S.never), b: S.number })
+    await Util.expectParseSuccess(schema, { b: 1 })
+    await Util.expectParseFailure(schema, { a: "a", b: 1 }, `/a Expected never, actual "a"`)
+  })
+
   it("all", async () => {
     const schema = S.struct({
       a: S.boolean,