From 39489ffb4dec953c85226c43cd771da94891fabb Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Sat, 2 Mar 2024 16:07:13 -0800
Subject: [PATCH] Revert contextual type check

---
 src/compiler/checker.ts                       |  2 --
 .../reference/findLast(target=esnext).types   | 22 +++++++++----------
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index af93bb8cfb2..432083640f3 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -37411,8 +37411,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // Only attempt to infer a type predicate if there's exactly one return.
         let singleReturn: Expression | undefined;
         if (func.body && func.body.kind !== SyntaxKind.Block) {
-            const contextualSignature = getContextualSignature(func as ArrowFunction);
-            if (contextualSignature && !getTypePredicateOfSignature(contextualSignature)) return undefined;
             singleReturn = func.body; // arrow function
         }
         else {
diff --git a/tests/baselines/reference/findLast(target=esnext).types b/tests/baselines/reference/findLast(target=esnext).types
index 6a608b9eb37..d010b65027b 100644
--- a/tests/baselines/reference/findLast(target=esnext).types
+++ b/tests/baselines/reference/findLast(target=esnext).types
@@ -170,7 +170,7 @@ const indexNumber: number = [0].findLastIndex((item) => item === 0);
 >[0] : number[]
 >0 : 0
 >findLastIndex : (predicate: (value: number, index: number, array: number[]) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -183,7 +183,7 @@ const indexString: number = ["string"].findLastIndex((item) => item === "string"
 >["string"] : string[]
 >"string" : "string"
 >findLastIndex : (predicate: (value: string, index: number, array: string[]) => unknown, thisArg?: any) => number
->(item) => item === "string" : (item: string) => boolean
+>(item) => item === "string" : (item: string) => item is "string"
 >item : string
 >item === "string" : boolean
 >item : string
@@ -195,7 +195,7 @@ new Int8Array().findLastIndex((item) => item === 0);
 >new Int8Array() : Int8Array
 >Int8Array : Int8ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Int8Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -207,7 +207,7 @@ new Uint8Array().findLastIndex((item) => item === 0);
 >new Uint8Array() : Uint8Array
 >Uint8Array : Uint8ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Uint8Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -219,7 +219,7 @@ new Uint8ClampedArray().findLastIndex((item) => item === 0);
 >new Uint8ClampedArray() : Uint8ClampedArray
 >Uint8ClampedArray : Uint8ClampedArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Uint8ClampedArray) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -231,7 +231,7 @@ new Int16Array().findLastIndex((item) => item === 0);
 >new Int16Array() : Int16Array
 >Int16Array : Int16ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Int16Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -243,7 +243,7 @@ new Uint16Array().findLastIndex((item) => item === 0);
 >new Uint16Array() : Uint16Array
 >Uint16Array : Uint16ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Uint16Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -255,7 +255,7 @@ new Int32Array().findLastIndex((item) => item === 0);
 >new Int32Array() : Int32Array
 >Int32Array : Int32ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Int32Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -267,7 +267,7 @@ new Uint32Array().findLastIndex((item) => item === 0);
 >new Uint32Array() : Uint32Array
 >Uint32Array : Uint32ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Uint32Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -279,7 +279,7 @@ new Float32Array().findLastIndex((item) => item === 0);
 >new Float32Array() : Float32Array
 >Float32Array : Float32ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Float32Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number
@@ -291,7 +291,7 @@ new Float64Array().findLastIndex((item) => item === 0);
 >new Float64Array() : Float64Array
 >Float64Array : Float64ArrayConstructor
 >findLastIndex : (predicate: (value: number, index: number, array: Float64Array) => unknown, thisArg?: any) => number
->(item) => item === 0 : (item: number) => boolean
+>(item) => item === 0 : (item: number) => item is 0
 >item : number
 >item === 0 : boolean
 >item : number