Reject unknown properties in Match.when object patterns

.changeset/tidy-cats-match.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Reject unknown properties in `Match.when` object patterns.

packages/effect/dtslint/Match.tst.ts

@@ -84,6 +84,15 @@ describe("Match", () => {
   })
 
   describe("when", () => {
+    it("rejects unknown object pattern properties", () => {
+      pipe(
+        Match.value(hole<{ _tag: "Transfer"; renamedValue: "foo" } | null>()),
+        // @ts-expect-error: Type 'string' is not assignable to type 'never'
+        Match.when({ _tag: "Transfer", value: "foo" }, () => {}),
+        Match.orElse(() => {})
+      )
+    })
+
     it("schema exhaustive-literal", () => {
       expect(
         pipe(

packages/effect/src/Match.ts

@@ -132,6 +132,16 @@ export interface ValueMatcher<in Input, out Filters, out Remaining, out Result,
  */
 export type Case = When | Not
 
+type PatternKeys<A> = A extends object ? keyof A : never
+
+type PatternGuard<A, P> = P extends
+  | Predicate.Predicate<any>
+  | Predicate.Refinement<any, any>
+  | SafeRefinement<any>
+  | ReadonlyArray<any> ? unknown
+  : P extends object ? { readonly [K in Exclude<keyof P, PatternKeys<A>>]: never }
+  : unknown
+
 /**
  * @category Model
  * @since 1.0.0
@@ -371,7 +381,7 @@ export const when: <
   Ret,
   Fn extends (_: Types.WhenMatch<R, P>) => Ret
 >(
-  pattern: P,
+  pattern: P & PatternGuard<R, P>,
   f: Fn
 ) => <I, F, A, Pr>(
   self: Matcher<I, F, R, A, Pr, Ret>
@@ -382,7 +392,7 @@ export const when: <
   A | ReturnType<Fn>,
   Pr,
   Ret
-> = internal.when
+> = internal.when as any
 
 /**
  * Matches one of multiple patterns in a single condition.