support QualifiedName when narrowing inside loops

src/compiler/binder.ts

@@ -2518,7 +2518,7 @@ namespace ts {
                     }
                     return checkContextualIdentifier(node as Identifier);
                 case SyntaxKind.QualifiedName:
-                    if (currentFlow && parent.kind === SyntaxKind.TypeQuery) {
+                    if (currentFlow && isPartOfTypeQuery(node)) {
                         node.flowNode = currentFlow;
                     }
                     break;

src/compiler/checker.ts

@@ -21956,6 +21956,9 @@ namespace ts {
                 case SyntaxKind.NonNullExpression:
                 case SyntaxKind.ParenthesizedExpression:
                     return getFlowCacheKey((node as NonNullExpression | ParenthesizedExpression).expression, declaredType, initialType, flowContainer);
+                case SyntaxKind.QualifiedName:
+                    const left = getFlowCacheKey((node as QualifiedName).left, declaredType, initialType, flowContainer);
+                    return left && left + "." + (node as QualifiedName).right.escapedText;
                 case SyntaxKind.PropertyAccessExpression:
                 case SyntaxKind.ElementAccessExpression:
                     const propName = getAccessedPropertyName(node as AccessExpression);

tests/baselines/reference/narrowingOfQualifiedNames.errors.txt

@@ -0,0 +1,74 @@
+tests/cases/compiler/narrowingOfQualifiedNames.ts(33,25): error TS2532: Object is possibly 'undefined'.
+tests/cases/compiler/narrowingOfQualifiedNames.ts(38,29): error TS2532: Object is possibly 'undefined'.
+
+
+==== tests/cases/compiler/narrowingOfQualifiedNames.ts (2 errors) ====
+    // Repro from #43411
+
+    interface IProperties {
+        foo?: {
+            aaa: string
+            bbb: string
+        }
+    }
+
+    function init(properties: IProperties) {
+        if (properties.foo) {
+            type FooOK = typeof properties.foo;
+            properties.foo; // type is { aaa: string; bbb: string; }
+            for (const x of [1, 2, 3]) {
+              properties.foo; // type is { aaa: string; bbb: string; }
+              type FooOrUndefined = typeof properties.foo; // type should be { aaa: string; bbb: string; }
+            }
+        }
+    }
+
+    interface DeepOptional {
+        a?: {
+            b?: {
+                c?: string
+            }
+        }
+    }
+
+    function init2(foo: DeepOptional) {
+        if (foo.a) {
+            type A = typeof foo.a;
+            type B = typeof foo.a.b;
+            type C = typeof foo.a.b.c;
+                            ~~~~~~~
+!!! error TS2532: Object is possibly 'undefined'.
+
+            for(const _ of [1]) {
+                type A = typeof foo.a;
+                type B = typeof foo.a.b;
+                type C = typeof foo.a.b.c;
+                                ~~~~~~~
+!!! error TS2532: Object is possibly 'undefined'.
+
+                if (foo.a.b) {
+                    type A = typeof foo.a;
+                    type B = typeof foo.a.b;
+                    type C = typeof foo.a.b.c;
+
+                    for(const _ of [1]) {
+                        type A = typeof foo.a;
+                        type B = typeof foo.a.b;
+                        type C = typeof foo.a.b.c;
+
+                        if (foo.a.b.c) {
+                            type A = typeof foo.a;
+                            type B = typeof foo.a.b;
+                            type C = typeof foo.a.b.c;
+
+                            for(const _ of [1]) {
+                                type A = typeof foo.a;
+                                type B = typeof foo.a.b;
+                                type C = typeof foo.a.b.c;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }

tests/baselines/reference/narrowingOfQualifiedNames.js

@@ -0,0 +1,96 @@
+//// [narrowingOfQualifiedNames.ts]
+// Repro from #43411
+
+interface IProperties {
+    foo?: {
+        aaa: string
+        bbb: string
+    }
+}
+
+function init(properties: IProperties) {
+    if (properties.foo) {
+        type FooOK = typeof properties.foo;
+        properties.foo; // type is { aaa: string; bbb: string; }
+        for (const x of [1, 2, 3]) {
+          properties.foo; // type is { aaa: string; bbb: string; }
+          type FooOrUndefined = typeof properties.foo; // type should be { aaa: string; bbb: string; }
+        }
+    }
+}
+
+interface DeepOptional {
+    a?: {
+        b?: {
+            c?: string
+        }
+    }
+}
+
+function init2(foo: DeepOptional) {
+    if (foo.a) {
+        type A = typeof foo.a;
+        type B = typeof foo.a.b;
+        type C = typeof foo.a.b.c;
+
+        for(const _ of [1]) {
+            type A = typeof foo.a;
+            type B = typeof foo.a.b;
+            type C = typeof foo.a.b.c;
+
+            if (foo.a.b) {
+                type A = typeof foo.a;
+                type B = typeof foo.a.b;
+                type C = typeof foo.a.b.c;
+
+                for(const _ of [1]) {
+                    type A = typeof foo.a;
+                    type B = typeof foo.a.b;
+                    type C = typeof foo.a.b.c;
+
+                    if (foo.a.b.c) {
+                        type A = typeof foo.a;
+                        type B = typeof foo.a.b;
+                        type C = typeof foo.a.b.c;
+
+                        for(const _ of [1]) {
+                            type A = typeof foo.a;
+                            type B = typeof foo.a.b;
+                            type C = typeof foo.a.b.c;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+//// [narrowingOfQualifiedNames.js]
+"use strict";
+// Repro from #43411
+function init(properties) {
+    if (properties.foo) {
+        properties.foo; // type is { aaa: string; bbb: string; }
+        for (var _i = 0, _a = [1, 2, 3]; _i < _a.length; _i++) {
+            var x = _a[_i];
+            properties.foo; // type is { aaa: string; bbb: string; }
+        }
+    }
+}
+function init2(foo) {
+    if (foo.a) {
+        for (var _i = 0, _a = [1]; _i < _a.length; _i++) {
+            var _ = _a[_i];
+            if (foo.a.b) {
+                for (var _b = 0, _c = [1]; _b < _c.length; _b++) {
+                    var _1 = _c[_b];
+                    if (foo.a.b.c) {
+                        for (var _d = 0, _e = [1]; _d < _e.length; _d++) {
+                            var _2 = _e[_d];
+                        }
+                    }
+                }
+            }
+        }
+    }
+}