Report "not a constructor" for a non-object new target

api-test.c

@@ -928,6 +928,88 @@ static void new_errors(void)
     JS_FreeRuntime(rt);
 }
 
+// Constructing something that is not a constructor reports "not a
+// constructor", never "not a function"; the latter is what *calling* a
+// non-callable reports.
+static void construct_not_a_constructor(void)
+{
+    JSValue not_objects[6];
+    JSValue obj, exc, ret;
+    JSClassID class_id;
+    const char *s;
+    size_t i;
+
+    // a class without a .call handler; an object of that class carrying the
+    // constructor bit is a constructor as far as the object header goes, but
+    // there is nothing to call
+    JSClassDef def = (JSClassDef){
+        .class_name = "NoCall",
+    };
+    JSRuntime *rt = new_runtime();
+    class_id = 0;
+    JS_NewClassID(rt, &class_id);
+    assert(JS_NewClass(rt, class_id, &def) == 0);
+    JSContext *ctx = JS_NewContext(rt);
+
+    obj = JS_NewObjectClass(ctx, class_id);
+    assert(JS_IsObject(obj));
+    assert(JS_SetConstructorBit(ctx, obj, true));
+    assert(JS_IsConstructor(ctx, obj));
+
+    ret = JS_CallConstructor(ctx, obj, 0, NULL);
+    assert(JS_IsException(ret));
+    JS_FreeValue(ctx, ret);
+    exc = JS_GetException(ctx);
+    s = JS_ToCString(ctx, exc);
+    assert(s);
+    assert(!strcmp(s, "TypeError: not a constructor"));
+    JS_FreeCString(ctx, s);
+    JS_FreeValue(ctx, exc);
+
+    // the same object reached through the interpreter's `new`
+    JSValue global = JS_GetGlobalObject(ctx);
+    JS_SetPropertyStr(ctx, global, "nocall", obj); // takes ownership
+    JS_FreeValue(ctx, global);
+    ret = eval(ctx, "try { new nocall() } catch (e) { `${e}` }");
+    assert(!JS_IsException(ret));
+    s = JS_ToCString(ctx, ret);
+    assert(s);
+    assert(!strcmp(s, "TypeError: not a constructor"));
+    JS_FreeCString(ctx, s);
+    JS_FreeValue(ctx, ret);
+
+    // and constructing a non-object
+    not_objects[0] = JS_UNDEFINED;
+    not_objects[1] = JS_NULL;
+    not_objects[2] = JS_TRUE;
+    not_objects[3] = JS_FALSE;
+    not_objects[4] = JS_NewInt32(ctx, 42);
+    not_objects[5] = JS_NewFloat64(ctx, 1.5);
+    for (i = 0; i < countof(not_objects); i++) {
+        ret = JS_CallConstructor(ctx, not_objects[i], 0, NULL);
+        assert(JS_IsException(ret));
+        JS_FreeValue(ctx, ret);
+        exc = JS_GetException(ctx);
+        s = JS_ToCString(ctx, exc);
+        assert(s);
+        assert(!strcmp(s, "TypeError: not a constructor"));
+        JS_FreeCString(ctx, s);
+        JS_FreeValue(ctx, exc);
+    }
+
+    // calling a non-callable is still "not a function"
+    ret = eval(ctx, "try { undefined() } catch (e) { `${e}` }");
+    assert(!JS_IsException(ret));
+    s = JS_ToCString(ctx, ret);
+    assert(s);
+    assert(!strcmp(s, "TypeError: not a function"));
+    JS_FreeCString(ctx, s);
+    JS_FreeValue(ctx, ret);
+
+    JS_FreeContext(ctx);
+    JS_FreeRuntime(rt);
+}
+
 static void backtrace_oom_callsite_array(void)
 {
     static const char setup_code[] =
@@ -1840,6 +1922,7 @@ int main(void)
     promise_hook();
     dump_memory_usage();
     new_errors();
+    construct_not_a_constructor();
     backtrace_oom_current_exception();
     backtrace_oom_callsite_array();
     proxy_own_keys_huge_length();

quickjs.c

@@ -21071,17 +21071,15 @@ static JSValue JS_CallConstructorInternal(JSContext *ctx,
         return JS_EXCEPTION;
     flags |= JS_CALL_FLAG_CONSTRUCTOR;
     if (unlikely(JS_VALUE_GET_TAG(func_obj) != JS_TAG_OBJECT))
-        goto not_a_function;
+        return JS_ThrowTypeErrorNotAConstructor(ctx, func_obj);
     p = JS_VALUE_GET_OBJ(func_obj);
     if (unlikely(!p->is_constructor))
         return JS_ThrowTypeErrorNotAConstructor(ctx, func_obj);
     if (unlikely(p->class_id != JS_CLASS_BYTECODE_FUNCTION)) {
         JSClassCall *call_func;
         call_func = ctx->rt->class_array[p->class_id].call;
-        if (!call_func) {
-        not_a_function:
-            return JS_ThrowTypeErrorNotAFunction(ctx);
-        }
+        if (!call_func)
+            return JS_ThrowTypeErrorNotAConstructor(ctx, func_obj);
         return call_func(ctx, func_obj, new_target, argc,
                          argv, flags);
     }

tests/new-not-a-constructor.js

@@ -0,0 +1,193 @@
+import { assert } from "./assert.js";
+
+/* `new x` where x is not an object is a "not a constructor" TypeError, the
+   same as `new x` on an object that is not a constructor. It used to be
+   reported as "not a function", which is what a *call* of a non-callable
+   reports; the two are distinct errors. */
+
+function message(fn) {
+    try {
+        fn();
+    } catch (e) {
+        assert(e instanceof TypeError, true);
+        return e.message;
+    }
+    return "<no throw>";
+}
+
+/* every primitive type, both as `new x` and `new x(...)` */
+{
+    const notObjects = [
+        ["undefined", undefined],
+        ["null", null],
+        ["boolean", true],
+        ["number", 1],
+        ["double", 1.5],
+        ["string", "x"],
+        ["symbol", Symbol.iterator],
+        ["bigint", 1n],
+    ];
+
+    for (const [what, v] of notObjects) {
+        assert(message(() => new v), "not a constructor", what);
+        assert(message(() => new v()), "not a constructor", `${what} ()`);
+        assert(message(() => new v(1, 2, 3)), "not a constructor",
+               `${what} (args)`);
+        assert(message(() => Reflect.construct(v, [])), "not a constructor",
+               `${what} Reflect.construct`);
+        assert(message(() => Reflect.construct(Object, [], v)),
+               "not a constructor", `${what} newTarget`);
+    }
+
+    /* a missing property and an undefined variable reach the same path */
+    const o = {};
+    assert(message(() => new o.missing()), "not a constructor");
+    assert(message(() => new o.missing), "not a constructor");
+}
+
+/* the arguments are still evaluated before the check, as for any call */
+{
+    let evaluated = 0;
+    const v = undefined;
+    assert(message(() => new v(evaluated++)), "not a constructor");
+    assert(evaluated, 1);
+}
+
+/* objects that are not constructors keep the same message */
+{
+    assert(message(() => new {}()), "not a constructor");
+    assert(message(() => new Math.max()), "not a constructor");
+    assert(message(() => new Symbol()), "not a constructor");
+    assert(message(() => new BigInt(1)), "not a constructor");
+    assert(message(() => new (() => {})()), "not a constructor");
+    assert(message(() => new (async function() {})()), "not a constructor");
+    assert(message(() => new (new Proxy({}, {}))()), "not a constructor");
+    assert(message(() => new (Reflect.construct)()), "not a constructor");
+}
+
+/* a named bytecode function still names itself in the message */
+{
+    function* g() {}
+    assert(message(() => new g()), "g is not a constructor");
+    assert(message(() => Reflect.construct(g, [])), "g is not a constructor");
+}
+
+/* `extends null` makes super() a construct of a non-object */
+{
+    class D extends null {
+        constructor() {
+            super();
+        }
+    }
+    assert(message(() => new D()), "not a constructor");
+}
+
+/* calling a non-callable is a *different* error and must keep its message */
+{
+    const v = undefined;
+    assert(message(() => v()), "not a function");
+    assert(message(() => (1)()), "not a function");
+    assert(message(() => "s"()), "not a function");
+    assert(message(() => ({})()), "not a function");
+    assert(message(() => Reflect.apply(undefined, null, [])),
+           "not a function");
+
+    const o = {};
+    assert(message(() => o.missing()), "not a function");
+}
+
+/* the function-shaped things that are still not constructors */
+{
+    function* gen() {}
+    async function* agen() {}
+    const obj = {
+        method() {},
+        *genMethod() {},
+        async asyncMethod() {},
+        get accessor() { return 1; },
+    };
+    class C {
+        method() {}
+        static staticMethod() {}
+        get accessor() { return 1; }
+    }
+    const accessor = Object.getOwnPropertyDescriptor(obj, "accessor").get;
+
+    const cases = [
+        ["generator", gen],
+        ["async generator", agen],
+        ["method shorthand", obj.method],
+        ["generator method", obj.genMethod],
+        ["async method", obj.asyncMethod],
+        ["getter", accessor],
+        ["class method", C.prototype.method],
+        ["static class method", C.staticMethod],
+        ["bound arrow", (() => {}).bind(null)],
+        ["bound method", obj.method.bind(null)],
+        ["proxy of a method", new Proxy(obj.method, {})],
+        ["proxy of an arrow", new Proxy(() => {}, {})],
+    ];
+    for (const [what, v] of cases) {
+        assert(typeof v, "function", what);
+        /* a named function names itself, so only the tail is fixed */
+        assert(message(() => new v()).endsWith("not a constructor"), true, what);
+        assert(message(() => Reflect.construct(v, [])).endsWith(
+                   "not a constructor"), true, `${what} via Reflect.construct`);
+        assert(message(() => Reflect.construct(Object, [], v)).endsWith(
+                   "not a constructor"), true, `${what} as new.target`);
+    }
+
+    /* ... and the ones that are */
+    for (const [what, v] of [["class", C], ["function", function() {}],
+                             ["bound function", (function() {}).bind(null)],
+                             ["proxy of a class", new Proxy(C, {})]]) {
+        const r = new v();
+        assert(typeof r, "object", what);
+    }
+}
+
+/* a revoked proxy reports a revoked proxy, not a missing constructor */
+{
+    const { proxy, revoke } = Proxy.revocable(function() {}, {});
+    assert(new proxy() instanceof Object, true);
+    revoke();
+    let caught = null;
+    try {
+        new proxy();
+    } catch (e) {
+        caught = e;
+    }
+    assert(caught instanceof TypeError, true);
+
+    const bad = Proxy.revocable({}, {});
+    bad.revoke();
+    let caught2 = null;
+    try {
+        new bad.proxy();
+    } catch (e) {
+        caught2 = e;
+    }
+    assert(caught2 instanceof TypeError, true);
+}
+
+/* super() in a derived class whose parent is not a constructor */
+{
+    const notCtor = () => {};
+    class D extends Object {
+        constructor() {
+            super();
+        }
+    }
+    assert(new D() instanceof D, true);
+
+    let caught = null;
+    try {
+        const E = class extends Object { constructor() { super(); } };
+        Object.setPrototypeOf(E, notCtor);
+        new E();
+    } catch (e) {
+        caught = e;
+    }
+    assert(caught instanceof TypeError, true);
+    assert(caught.message.includes("not a constructor"), true);
+}