Fix narrow-by-constructor logic

src/compiler/checker.ts

@@ -20265,12 +20265,6 @@ namespace ts {
                         if (right.kind === SyntaxKind.TypeOfExpression && isStringLiteralLike(left)) {
                             return narrowTypeByTypeof(type, <TypeOfExpression>right, operator, left, assumeTrue);
                         }
-                        if (isConstructorAccessExpression(left)) {
-                            return narrowTypeByConstructor(type, left, operator, right, assumeTrue);
-                        }
-                        if (isConstructorAccessExpression(right)) {
-                            return narrowTypeByConstructor(type, right, operator, left, assumeTrue);
-                        }
                         if (isMatchingReference(reference, left)) {
                             return narrowTypeByEquality(type, operator, right, assumeTrue);
                         }
@@ -20291,6 +20285,12 @@ namespace ts {
                         if (isMatchingReferenceDiscriminant(right, declaredType)) {
                             return narrowTypeByDiscriminant(type, <AccessExpression>right, t => narrowTypeByEquality(t, operator, left, assumeTrue));
                         }
+                        if (isMatchingConstructorReference(left)) {
+                            return narrowTypeByConstructor(type, operator, right, assumeTrue);
+                        }
+                        if (isMatchingConstructorReference(right)) {
+                            return narrowTypeByConstructor(type, operator, left, assumeTrue);
+                        }
                         break;
                     case SyntaxKind.InstanceOfKeyword:
                         return narrowTypeByInstanceof(type, expr, assumeTrue);
@@ -20564,17 +20564,18 @@ namespace ts {
                 return getTypeWithFacts(mapType(type, narrowTypeForTypeofSwitch(impliedType)), switchFacts);
             }
 
-            function narrowTypeByConstructor(type: Type, constructorAccessExpr: AccessExpression, operator: SyntaxKind, identifier: Expression, assumeTrue: boolean): Type {
+            function isMatchingConstructorReference(expr: Expression) {
+                return (isPropertyAccessExpression(expr) && idText(expr.name) === "constructor" ||
+                    isElementAccessExpression(expr) && isStringLiteralLike(expr.argumentExpression) && expr.argumentExpression.text === "constructor") &&
+                    isMatchingReference(reference, expr.expression);
+            }
+
+            function narrowTypeByConstructor(type: Type, operator: SyntaxKind, identifier: Expression, assumeTrue: boolean): Type {
                 // Do not narrow when checking inequality.
                 if (assumeTrue ? (operator !== SyntaxKind.EqualsEqualsToken && operator !== SyntaxKind.EqualsEqualsEqualsToken) : (operator !== SyntaxKind.ExclamationEqualsToken && operator !== SyntaxKind.ExclamationEqualsEqualsToken)) {
                     return type;
                 }
 
-                // In the case of `x.y`, a `x.constructor === T` type guard resets the narrowed type of `y` to its declared type.
-                if (!isMatchingReference(reference, constructorAccessExpr.expression)) {
-                    return declaredType;
-                }
-
                 // Get the type of the constructor identifier expression, if it is not a function then do not narrow.
                 const identifierType = getTypeOfExpression(identifier);
                 if (!isFunctionType(identifierType) && !isConstructorType(identifierType)) {

src/compiler/utilities.ts

@@ -4432,13 +4432,6 @@ namespace ts {
         return isPropertyAccessExpression(node) && isEntityNameExpression(node.expression);
     }
 
-    export function isConstructorAccessExpression(expr: Expression): expr is AccessExpression {
-        return (
-            isPropertyAccessExpression(expr) && idText(expr.name) === "constructor" ||
-            isElementAccessExpression(expr) && isStringLiteralLike(expr.argumentExpression) && expr.argumentExpression.text === "constructor"
-        );
-    }
-
     export function tryGetPropertyAccessOrIdentifierToString(expr: Expression): string | undefined {
         if (isPropertyAccessExpression(expr)) {
             const baseStr = tryGetPropertyAccessOrIdentifierToString(expr.expression);

tests/baselines/reference/typeGuardConstructorClassAndNumber.errors.txt

@@ -160,4 +160,14 @@ tests/cases/compiler/typeGuardConstructorClassAndNumber.ts(115,10): error TS2339
     else {
         var1; // C1
     }
+
+    // Repro from #37660
+
+    function foo(instance: Function | object) {
+        if (typeof instance === 'function') {
+            if (instance.prototype == null || instance.prototype.constructor == null) {
+                return instance.length;
+            }
+        }
+    }
 

tests/baselines/reference/typeGuardConstructorClassAndNumber.js

@@ -118,6 +118,16 @@ if (C1 !== var1["constructor"]) {
 else {
     var1; // C1
 }
+
+// Repro from #37660
+
+function foo(instance: Function | object) {
+    if (typeof instance === 'function') {
+        if (instance.prototype == null || instance.prototype.constructor == null) {
+            return instance.length;
+        }
+    }
+}
 
 
 //// [typeGuardConstructorClassAndNumber.js]
@@ -240,3 +250,11 @@ if (C1 !== var1["constructor"]) {
 else {
     var1; // C1
 }
+// Repro from #37660
+function foo(instance) {
+    if (typeof instance === 'function') {
+        if (instance.prototype == null || instance.prototype.constructor == null) {
+            return instance.length;
+        }
+    }
+}

tests/baselines/reference/typeGuardConstructorClassAndNumber.symbols

@@ -277,3 +277,29 @@ else {
 >var1 : Symbol(var1, Decl(typeGuardConstructorClassAndNumber.ts, 5, 3))
 }
 
+// Repro from #37660
+
+function foo(instance: Function | object) {
+>foo : Symbol(foo, Decl(typeGuardConstructorClassAndNumber.ts, 118, 1))
+>instance : Symbol(instance, Decl(typeGuardConstructorClassAndNumber.ts, 122, 13))
+>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    if (typeof instance === 'function') {
+>instance : Symbol(instance, Decl(typeGuardConstructorClassAndNumber.ts, 122, 13))
+
+        if (instance.prototype == null || instance.prototype.constructor == null) {
+>instance.prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+>instance : Symbol(instance, Decl(typeGuardConstructorClassAndNumber.ts, 122, 13))
+>prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+>instance.prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+>instance : Symbol(instance, Decl(typeGuardConstructorClassAndNumber.ts, 122, 13))
+>prototype : Symbol(Function.prototype, Decl(lib.es5.d.ts, --, --))
+
+            return instance.length;
+>instance.length : Symbol(Function.length, Decl(lib.es5.d.ts, --, --))
+>instance : Symbol(instance, Decl(typeGuardConstructorClassAndNumber.ts, 122, 13))
+>length : Symbol(Function.length, Decl(lib.es5.d.ts, --, --))
+        }
+    }
+}
+

tests/baselines/reference/typeGuardConstructorClassAndNumber.types

@@ -316,3 +316,38 @@ else {
 >var1 : C1
 }
 
+// Repro from #37660
+
+function foo(instance: Function | object) {
+>foo : (instance: object | Function) => number
+>instance : object | Function
+
+    if (typeof instance === 'function') {
+>typeof instance === 'function' : boolean
+>typeof instance : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>instance : object | Function
+>'function' : "function"
+
+        if (instance.prototype == null || instance.prototype.constructor == null) {
+>instance.prototype == null || instance.prototype.constructor == null : boolean
+>instance.prototype == null : boolean
+>instance.prototype : any
+>instance : Function
+>prototype : any
+>null : null
+>instance.prototype.constructor == null : boolean
+>instance.prototype.constructor : any
+>instance.prototype : any
+>instance : Function
+>prototype : any
+>constructor : any
+>null : null
+
+            return instance.length;
+>instance.length : number
+>instance : Function
+>length : number
+        }
+    }
+}
+

tests/cases/compiler/typeGuardConstructorClassAndNumber.ts

@@ -117,3 +117,13 @@ if (C1 !== var1["constructor"]) {
 else {
     var1; // C1
 }
+
+// Repro from #37660
+
+function foo(instance: Function | object) {
+    if (typeof instance === 'function') {
+        if (instance.prototype == null || instance.prototype.constructor == null) {
+            return instance.length;
+        }
+    }
+}