v5: better support for wrong patterns resulting in the 'any' type

Author: gvergnaud

src/types/ExtractPreciseValue.ts

@@ -12,7 +12,11 @@ import { DeepExclude } from './DeepExclude';
 
 export type ExtractPreciseValue<a, b> = unknown extends b
   ? a
-  : IsAny<a> extends true
+  : // inlining IsAny for perf
+  0 extends 1 & b
+  ? a
+  : // inlining IsAny for perf
+  0 extends 1 & a
   ? b
   : b extends readonly []
   ? []

src/types/FindSelected.ts

@@ -94,7 +94,11 @@ export type FindSelectionUnion<
   p,
   // path just serves as an id, to identify different anonymous patterns which have the same type
   path extends any[] = []
-> = IsAny<i> extends true
+  // inlining IsAny for perf
+> = 0 extends 1 & i
+  ? never
+  : // inlining IsAny for perf
+  0 extends 1 & p
   ? never
   : p extends Primitives
   ? never

src/types/InvertPattern.ts

@@ -14,7 +14,10 @@ import {
 import type { Matcher, Pattern, ToExclude, AnyMatcher } from './Pattern';
 
 type OptionalKeys<p> = ValueOf<{
-  [k in keyof p]: p[k] extends Matcher<any, any, infer matcherType>
+  [k in keyof p]: // inlining IsAny for perf
+  0 extends 1 & p[k]
+    ? never
+    : p[k] extends Matcher<any, any, infer matcherType>
     ? matcherType extends 'optional'
       ? k
       : never
@@ -59,12 +62,9 @@ type InvertArrayPattern<
  * Since patterns have special wildcard values, we need a way
  * to transform a pattern into the type of value it represents
  */
-export type InvertPattern<p> = p extends Matcher<
-  infer input,
-  infer narrowed,
-  infer matcherType,
-  any
->
+export type InvertPattern<p> = 0 extends 1 & p
+  ? never
+  : p extends Matcher<infer input, infer narrowed, infer matcherType, any>
   ? {
       not: ToExclude<InvertPattern<narrowed>>;
       select: InvertPattern<narrowed>;

src/types/Match.ts

@@ -37,8 +37,7 @@ export type Match<
   with<
     const p extends Pattern<i>,
     c,
-    value extends MatchedValue<i, InvertPattern<p>>,
-    x = InvertPatternForExclude<p, MatchedValue<i, InvertPattern<p>>>
+    value extends MatchedValue<i, InvertPattern<p>>
   >(
     /**
      * HACK: Using `IsNever<p>` here is a hack to

tests/type-error.test.ts

@@ -115,4 +115,15 @@ describe('type errors', () => {
         // @ts-expect-error
         .exhaustive();
   });
+
+  it("if a pattern is any, the outer expression shouldn't throw a type error", () => {
+    const anyVar = null as any;
+
+    match({ a: 'a' })
+      .with({ a: anyVar }, (x) => {
+        type t = Expect<Equal<typeof x, { a: never }>>;
+        return 'Ok';
+      })
+      .otherwise(() => 'ko');
+  });
 });