From a7e8230cf138364a2f23c042b2349d6b5cc240ba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Tue, 2 Dec 2025 20:07:40 +0100
Subject: [PATCH] Simplify `never` indexed by generic index types

---
 src/compiler/checker.ts                           |  2 +-
 .../reference/keyofAndIndexedAccess.errors.txt    |  4 ++++
 .../baselines/reference/keyofAndIndexedAccess.js  |  7 +++++++
 .../reference/keyofAndIndexedAccess.symbols       | 15 +++++++++++++++
 .../reference/keyofAndIndexedAccess.types         | 12 ++++++++++++
 .../types/keyof/keyofAndIndexedAccess.ts          |  4 ++++
 6 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8e5c03560db3e..f089844a992b6 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -19611,7 +19611,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 isGenericTupleType(objectType) && !indexTypeLessThan(indexType, getTotalFixedElementCount(objectType.target)) :
                 isGenericObjectType(objectType) && !(isTupleType(objectType) && indexTypeLessThan(indexType, getTotalFixedElementCount(objectType.target))) || isGenericReducibleType(objectType))
         ) {
-            if (objectType.flags & TypeFlags.AnyOrUnknown) {
+            if (objectType.flags & (TypeFlags.AnyOrUnknown | TypeFlags.Never)) {
                 return objectType;
             }
             // Defer the operation by creating an indexed access type.
diff --git a/tests/baselines/reference/keyofAndIndexedAccess.errors.txt b/tests/baselines/reference/keyofAndIndexedAccess.errors.txt
index e833106df6fe5..05f425708bb02 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess.errors.txt
+++ b/tests/baselines/reference/keyofAndIndexedAccess.errors.txt
@@ -694,4 +694,8 @@ keyofAndIndexedAccess.ts(318,5): error TS2322: Type 'T[K]' is not assignable to
         const s: string = t[k];
         t.cool;
     };
+    
+    type IndexedNever<T> = never[keyof T];
+    type IndexedAny<T> = any[keyof T];
+    type IndexedUnknown<T> = unknown[keyof T];
     
\ No newline at end of file
diff --git a/tests/baselines/reference/keyofAndIndexedAccess.js b/tests/baselines/reference/keyofAndIndexedAccess.js
index ea10cf32f5e50..fd718fe3853e9 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess.js
+++ b/tests/baselines/reference/keyofAndIndexedAccess.js
@@ -658,6 +658,10 @@ const cf2 = <T extends { [P in K | "cool"]: string; }, K extends keyof T>(t: T,
     const s: string = t[k];
     t.cool;
 };
+
+type IndexedNever<T> = never[keyof T];
+type IndexedAny<T> = any[keyof T];
+type IndexedUnknown<T> = unknown[keyof T];
 
 
 //// [keyofAndIndexedAccess.js]
@@ -1435,3 +1439,6 @@ declare const cf1: <T extends { [P in K]: string; } & {
     cool: string;
 }, K extends keyof T>(t: T, k: K) => void;
 declare const cf2: <T extends { [P in K | "cool"]: string; }, K extends keyof T>(t: T, k: K) => void;
+type IndexedNever<T> = never[keyof T];
+type IndexedAny<T> = any[keyof T];
+type IndexedUnknown<T> = unknown[keyof T];
diff --git a/tests/baselines/reference/keyofAndIndexedAccess.symbols b/tests/baselines/reference/keyofAndIndexedAccess.symbols
index 0d2b7218d5b0b..4520374edee31 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccess.symbols
@@ -2345,3 +2345,18 @@ const cf2 = <T extends { [P in K | "cool"]: string; }, K extends keyof T>(t: T,
 
 };
 
+type IndexedNever<T> = never[keyof T];
+>IndexedNever : Symbol(IndexedNever, Decl(keyofAndIndexedAccess.ts, 656, 2))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 658, 18))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 658, 18))
+
+type IndexedAny<T> = any[keyof T];
+>IndexedAny : Symbol(IndexedAny, Decl(keyofAndIndexedAccess.ts, 658, 38))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 659, 16))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 659, 16))
+
+type IndexedUnknown<T> = unknown[keyof T];
+>IndexedUnknown : Symbol(IndexedUnknown, Decl(keyofAndIndexedAccess.ts, 659, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 660, 20))
+>T : Symbol(T, Decl(keyofAndIndexedAccess.ts, 660, 20))
+
diff --git a/tests/baselines/reference/keyofAndIndexedAccess.types b/tests/baselines/reference/keyofAndIndexedAccess.types
index 6f0d4daec7e44..aa6256d0029fc 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess.types
+++ b/tests/baselines/reference/keyofAndIndexedAccess.types
@@ -3450,3 +3450,15 @@ const cf2 = <T extends { [P in K | "cool"]: string; }, K extends keyof T>(t: T,
 
 };
 
+type IndexedNever<T> = never[keyof T];
+>IndexedNever : never
+>             : ^^^^^
+
+type IndexedAny<T> = any[keyof T];
+>IndexedAny : any
+>           : ^^^
+
+type IndexedUnknown<T> = unknown[keyof T];
+>IndexedUnknown : unknown
+>               : ^^^^^^^
+
diff --git a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts
index 56ff157a67fd0..166ed6f36fc5a 100644
--- a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts
+++ b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts
@@ -658,3 +658,7 @@ const cf2 = <T extends { [P in K | "cool"]: string; }, K extends keyof T>(t: T,
     const s: string = t[k];
     t.cool;
 };
+
+type IndexedNever<T> = never[keyof T];
+type IndexedAny<T> = any[keyof T];
+type IndexedUnknown<T> = unknown[keyof T];