fix flow type of this inside arrow function (#54236)

Author: Zzzen

src/compiler/checker.ts

@@ -26572,7 +26572,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     if (container && container !== flowContainer &&
                         reference.kind !== SyntaxKind.PropertyAccessExpression &&
                         reference.kind !== SyntaxKind.ElementAccessExpression &&
-                        reference.kind !== SyntaxKind.ThisKeyword) {
+                        !(reference.kind === SyntaxKind.ThisKeyword && container.kind !== SyntaxKind.ArrowFunction)
+                    ) {
                         flow = container.flowNode!;
                         continue;
                     }

tests/baselines/reference/thisTypeInFunctions4.js

@@ -0,0 +1,28 @@
+//// [thisTypeInFunctions4.ts]
+type WrongObject = {value: number};
+type CorrectObject = {name: string};
+
+declare function isCorrect(obj: any): obj is CorrectObject
+
+declare function callsCallback(cb: (name: string)=>void)
+
+function problemFunction(this: CorrectObject | WrongObject): void {
+    //check type
+    if (!isCorrect(this)) return;
+
+    callsCallback((name)=>{
+        this.name = name; //should not error
+        type T = typeof this;
+    });
+}
+
+//// [thisTypeInFunctions4.js]
+function problemFunction() {
+    var _this = this;
+    //check type
+    if (!isCorrect(this))
+        return;
+    callsCallback(function (name) {
+        _this.name = name; //should not error
+    });
+}

tests/baselines/reference/thisTypeInFunctions4.symbols

@@ -0,0 +1,47 @@
+=== tests/cases/conformance/types/thisType/thisTypeInFunctions4.ts ===
+type WrongObject = {value: number};
+>WrongObject : Symbol(WrongObject, Decl(thisTypeInFunctions4.ts, 0, 0))
+>value : Symbol(value, Decl(thisTypeInFunctions4.ts, 0, 20))
+
+type CorrectObject = {name: string};
+>CorrectObject : Symbol(CorrectObject, Decl(thisTypeInFunctions4.ts, 0, 35))
+>name : Symbol(name, Decl(thisTypeInFunctions4.ts, 1, 22))
+
+declare function isCorrect(obj: any): obj is CorrectObject
+>isCorrect : Symbol(isCorrect, Decl(thisTypeInFunctions4.ts, 1, 36))
+>obj : Symbol(obj, Decl(thisTypeInFunctions4.ts, 3, 27))
+>obj : Symbol(obj, Decl(thisTypeInFunctions4.ts, 3, 27))
+>CorrectObject : Symbol(CorrectObject, Decl(thisTypeInFunctions4.ts, 0, 35))
+
+declare function callsCallback(cb: (name: string)=>void)
+>callsCallback : Symbol(callsCallback, Decl(thisTypeInFunctions4.ts, 3, 58))
+>cb : Symbol(cb, Decl(thisTypeInFunctions4.ts, 5, 31))
+>name : Symbol(name, Decl(thisTypeInFunctions4.ts, 5, 36))
+
+function problemFunction(this: CorrectObject | WrongObject): void {
+>problemFunction : Symbol(problemFunction, Decl(thisTypeInFunctions4.ts, 5, 56))
+>this : Symbol(this, Decl(thisTypeInFunctions4.ts, 7, 25))
+>CorrectObject : Symbol(CorrectObject, Decl(thisTypeInFunctions4.ts, 0, 35))
+>WrongObject : Symbol(WrongObject, Decl(thisTypeInFunctions4.ts, 0, 0))
+
+    //check type
+    if (!isCorrect(this)) return;
+>isCorrect : Symbol(isCorrect, Decl(thisTypeInFunctions4.ts, 1, 36))
+>this : Symbol(this, Decl(thisTypeInFunctions4.ts, 7, 25))
+
+    callsCallback((name)=>{
+>callsCallback : Symbol(callsCallback, Decl(thisTypeInFunctions4.ts, 3, 58))
+>name : Symbol(name, Decl(thisTypeInFunctions4.ts, 11, 19))
+
+        this.name = name; //should not error
+>this.name : Symbol(name, Decl(thisTypeInFunctions4.ts, 1, 22))
+>this : Symbol(this, Decl(thisTypeInFunctions4.ts, 7, 25))
+>name : Symbol(name, Decl(thisTypeInFunctions4.ts, 1, 22))
+>name : Symbol(name, Decl(thisTypeInFunctions4.ts, 11, 19))
+
+        type T = typeof this;
+>T : Symbol(T, Decl(thisTypeInFunctions4.ts, 12, 25))
+>this : Symbol(this, Decl(thisTypeInFunctions4.ts, 7, 25))
+
+    });
+}

tests/baselines/reference/thisTypeInFunctions4.types

@@ -0,0 +1,48 @@
+=== tests/cases/conformance/types/thisType/thisTypeInFunctions4.ts ===
+type WrongObject = {value: number};
+>WrongObject : { value: number; }
+>value : number
+
+type CorrectObject = {name: string};
+>CorrectObject : { name: string; }
+>name : string
+
+declare function isCorrect(obj: any): obj is CorrectObject
+>isCorrect : (obj: any) => obj is CorrectObject
+>obj : any
+
+declare function callsCallback(cb: (name: string)=>void)
+>callsCallback : (cb: (name: string) => void) => any
+>cb : (name: string) => void
+>name : string
+
+function problemFunction(this: CorrectObject | WrongObject): void {
+>problemFunction : (this: CorrectObject | WrongObject) => void
+>this : WrongObject | CorrectObject
+
+    //check type
+    if (!isCorrect(this)) return;
+>!isCorrect(this) : boolean
+>isCorrect(this) : boolean
+>isCorrect : (obj: any) => obj is CorrectObject
+>this : WrongObject | CorrectObject
+
+    callsCallback((name)=>{
+>callsCallback((name)=>{        this.name = name; //should not error        type T = typeof this;    }) : any
+>callsCallback : (cb: (name: string) => void) => any
+>(name)=>{        this.name = name; //should not error        type T = typeof this;    } : (name: string) => void
+>name : string
+
+        this.name = name; //should not error
+>this.name = name : string
+>this.name : string
+>this : CorrectObject
+>name : string
+>name : string
+
+        type T = typeof this;
+>T : CorrectObject
+>this : CorrectObject
+
+    });
+}

tests/cases/conformance/types/thisType/thisTypeInFunctions4.ts

@@ -0,0 +1,16 @@
+type WrongObject = {value: number};
+type CorrectObject = {name: string};
+
+declare function isCorrect(obj: any): obj is CorrectObject
+
+declare function callsCallback(cb: (name: string)=>void)
+
+function problemFunction(this: CorrectObject | WrongObject): void {
+    //check type
+    if (!isCorrect(this)) return;
+
+    callsCallback((name)=>{
+        this.name = name; //should not error
+        type T = typeof this;
+    });
+}