Narrow QualifiedName inside typeof (microsoft#42540)

Previously this wasn't narrowed at all. Now there is control flow and
code in isMatchingReference.

Author: sandersn

src/compiler/binder.ts

@@ -2540,6 +2540,11 @@ namespace ts {
                         node.flowNode = currentFlow;
                     }
                     return checkContextualIdentifier(<Identifier>node);
+                case SyntaxKind.QualifiedName:
+                    if (currentFlow && parent.kind === SyntaxKind.TypeQuery) {
+                        node.flowNode = currentFlow;
+                    }
+                    break;
                 case SyntaxKind.SuperKeyword:
                     node.flowNode = currentFlow;
                     break;

src/compiler/checker.ts

@@ -21289,8 +21289,12 @@ namespace ts {
                 case SyntaxKind.PropertyAccessExpression:
                 case SyntaxKind.ElementAccessExpression:
                     return isAccessExpression(target) &&
-                        getAccessedPropertyName(<AccessExpression>source) === getAccessedPropertyName(target) &&
-                        isMatchingReference((<AccessExpression>source).expression, target.expression);
+                        getAccessedPropertyName(source as AccessExpression) === getAccessedPropertyName(target) &&
+                        isMatchingReference((source as AccessExpression).expression, target.expression);
+                case SyntaxKind.QualifiedName:
+                    return isAccessExpression(target) &&
+                        (source as QualifiedName).right.escapedText === getAccessedPropertyName(target) &&
+                        isMatchingReference((source as QualifiedName).left, target.expression);
                 case SyntaxKind.BinaryExpression:
                     return (isBinaryExpression(source) && source.operatorToken.kind === SyntaxKind.CommaToken && isMatchingReference(source.right, target));
             }
@@ -26421,8 +26425,7 @@ namespace ts {
             // assignment target, and the referenced property was declared as a variable, property,
             // accessor, or optional method.
             const assignmentKind = getAssignmentTargetKind(node);
-            if (!isAccessExpression(node) ||
-                assignmentKind === AssignmentKind.Definite ||
+            if (assignmentKind === AssignmentKind.Definite ||
                 prop && !(prop.flags & (SymbolFlags.Variable | SymbolFlags.Property | SymbolFlags.Accessor)) && !(prop.flags & SymbolFlags.Method && propType.flags & TypeFlags.Union)) {
                 return propType;
             }
@@ -26434,7 +26437,7 @@ namespace ts {
             // and if we are in a constructor of the same class as the property declaration, assume that
             // the property is uninitialized at the top of the control flow.
             let assumeUninitialized = false;
-            if (strictNullChecks && strictPropertyInitialization && node.expression.kind === SyntaxKind.ThisKeyword) {
+            if (strictNullChecks && strictPropertyInitialization && isAccessExpression(node) && node.expression.kind === SyntaxKind.ThisKeyword) {
                 const declaration = prop && prop.valueDeclaration;
                 if (declaration && isInstancePropertyWithoutInitializer(declaration)) {
                     const flowContainer = getControlFlowContainer(node);

tests/baselines/reference/controlFlowIfStatement.js

@@ -51,6 +51,15 @@ function d<T extends string>(data: string | T): never {
         return data;
     }
 }
+
+interface I<T> {
+  p: T;
+}
+function e(x: I<"A" | "B">) {
+    if (x.p === "A") {
+        let a: "A" = (null as unknown as typeof x.p)
+    }
+}
 
 
 //// [controlFlowIfStatement.js]
@@ -104,3 +113,8 @@ function d(data) {
         return data;
     }
 }
+function e(x) {
+    if (x.p === "A") {
+        var a_1 = null;
+    }
+}

tests/baselines/reference/controlFlowIfStatement.symbols

@@ -110,3 +110,29 @@ function d<T extends string>(data: string | T): never {
     }
 }
 
+interface I<T> {
+>I : Symbol(I, Decl(controlFlowIfStatement.ts, 51, 1))
+>T : Symbol(T, Decl(controlFlowIfStatement.ts, 53, 12))
+
+  p: T;
+>p : Symbol(I.p, Decl(controlFlowIfStatement.ts, 53, 16))
+>T : Symbol(T, Decl(controlFlowIfStatement.ts, 53, 12))
+}
+function e(x: I<"A" | "B">) {
+>e : Symbol(e, Decl(controlFlowIfStatement.ts, 55, 1))
+>x : Symbol(x, Decl(controlFlowIfStatement.ts, 56, 11))
+>I : Symbol(I, Decl(controlFlowIfStatement.ts, 51, 1))
+
+    if (x.p === "A") {
+>x.p : Symbol(I.p, Decl(controlFlowIfStatement.ts, 53, 16))
+>x : Symbol(x, Decl(controlFlowIfStatement.ts, 56, 11))
+>p : Symbol(I.p, Decl(controlFlowIfStatement.ts, 53, 16))
+
+        let a: "A" = (null as unknown as typeof x.p)
+>a : Symbol(a, Decl(controlFlowIfStatement.ts, 58, 11))
+>x.p : Symbol(I.p, Decl(controlFlowIfStatement.ts, 53, 16))
+>x : Symbol(x, Decl(controlFlowIfStatement.ts, 56, 11))
+>p : Symbol(I.p, Decl(controlFlowIfStatement.ts, 53, 16))
+    }
+}
+

tests/baselines/reference/controlFlowIfStatement.types

@@ -132,3 +132,30 @@ function d<T extends string>(data: string | T): never {
     }
 }
 
+interface I<T> {
+  p: T;
+>p : T
+}
+function e(x: I<"A" | "B">) {
+>e : (x: I<"A" | "B">) => void
+>x : I<"A" | "B">
+
+    if (x.p === "A") {
+>x.p === "A" : boolean
+>x.p : "A" | "B"
+>x : I<"A" | "B">
+>p : "A" | "B"
+>"A" : "A"
+
+        let a: "A" = (null as unknown as typeof x.p)
+>a : "A"
+>(null as unknown as typeof x.p) : "A"
+>null as unknown as typeof x.p : "A"
+>null as unknown : unknown
+>null : null
+>x.p : "A"
+>x : I<"A" | "B">
+>p : "A"
+    }
+}
+

tests/cases/conformance/controlFlow/controlFlowIfStatement.ts

@@ -52,3 +52,12 @@ function d<T extends string>(data: string | T): never {
         return data;
     }
 }
+
+interface I<T> {
+  p: T;
+}
+function e(x: I<"A" | "B">) {
+    if (x.p === "A") {
+        let a: "A" = (null as unknown as typeof x.p)
+    }
+}