Admit direct arguments reads in Test262 scripts

tests/harness/test262-runner.test.ts

@@ -73,6 +73,18 @@ test("receiver-bound this is admitted without adapting script-level this", () =>
   }
 });
 
+test("arguments reads are admitted only for indexed and length access inside a function", () => {
+  for (const [body, expected] of [
+    ["function f() { return arguments.length === 1 && arguments[0] === 3; } assert(f(3));", undefined],
+    ["function f() { return arguments; }", "host:arguments"],
+    ["function f() { return Array.isArray(arguments); }", "host:arguments"],
+    ["assert.sameValue(arguments.length, 0);", "host:arguments"],
+  ]) {
+    const text = source("description: arguments", body!);
+    expect(exclusion(text, metadata(text), "strict")).toBe(expected);
+  }
+});
+
 test("negative parse cases require the compiler's matching source diagnostic", () => {
   const text = source("negative: {phase: parse, type: SyntaxError}", "$DONOTEVALUATE();\nconst = ;");
   expect(exclusion(text, metadata(text), "strict")).toBeUndefined();

tests/test262/support.mjs

@@ -95,6 +95,14 @@ function hasOwnThisBinding(node) {
   return false;
 }
 
+function argumentsOwner(node) {
+  for (let parent = node.parent; parent; parent = parent.parent) {
+    if (ts.isArrowFunction(parent)) continue;
+    if (ts.isFunctionLike(parent) && parent.body) return parent;
+  }
+  return undefined;
+}
+
 // The first static profile adapts scripts to standalone strict modules. Be
 // conservative about observable global-script semantics and helper reflection.
 // Exclusions are runner limitations, never implementation support claims.
@@ -111,7 +119,7 @@ export function exclusion(source, meta, variant) {
   if (unsupportedIncludes.length) return `harness-includes:${unsupportedIncludes.join(",")}`;
   const sf = ts.createSourceFile("test.js", source, ts.ScriptTarget.Latest, true, ts.ScriptKind.JS);
   let reason;
-  const forbidden = new Set(["$262", "$DONE", "$DONOTEVALUATE", "globalThis", "eval", "Function", "print", "process", "require", "arguments"]);
+  const forbidden = new Set(["$262", "$DONE", "$DONOTEVALUATE", "globalThis", "eval", "Function", "print", "process", "require"]);
   if (variant === "sloppy") for (const name of ["module", "exports", "__dirname", "__filename"]) forbidden.add(name);
   if (meta.flags.includes("async")) forbidden.delete("$DONE");
   const visit = (node) => {
@@ -121,6 +129,11 @@ export function exclusion(source, meta, variant) {
       reason = "host:script-environment";
     } else if (ts.isIdentifier(node) && forbidden.has(node.text)) {
       reason = `host:${node.text}`;
+    } else if (ts.isIdentifier(node) && node.text === "arguments" &&
+      (!argumentsOwner(node) ||
+        !(ts.isPropertyAccessExpression(node.parent) && node.parent.expression === node && node.parent.name.text === "length") &&
+        !(ts.isElementAccessExpression(node.parent) && node.parent.expression === node))) {
+      reason = "host:arguments";
     } else if (ts.isIdentifier(node) && node.text === "assert") {
       const parent = node.parent;
       if (ts.isCallExpression(parent) && parent.expression === node) {

tests/test262/upstream.json

@@ -168,6 +168,8 @@
     "test/built-ins/String/prototype/trim/15.5.4.20-2-47.js",
     "test/built-ins/String/prototype/trim/15.5.4.20-2-50.js",
     "test/built-ins/String/prototype/trim/15.5.4.20-2-6.js",
+    "test/language/arguments-object/func-decl-args-trailing-comma-null.js",
+    "test/language/arguments-object/func-expr-args-trailing-comma-undefined.js",
     "test/language/expressions/addition/S11.6.1_A4_T1.js",
     "test/language/expressions/addition/S11.6.1_A4_T2.js",
     "test/language/expressions/addition/S11.6.1_A4_T3.js",
@@ -372,6 +374,8 @@
     "test/built-ins/String/prototype/trim/15.5.4.20-2-47.js": "3e1a745af465177a96a29601e56299afc044060dbc2ac3061a59032be451cfde",
     "test/built-ins/String/prototype/trim/15.5.4.20-2-50.js": "38b84997faa99e422408917eeac7f3575bd6064b429ea390a9d041fd77fce532",
     "test/built-ins/String/prototype/trim/15.5.4.20-2-6.js": "3d5857f24117f65f07a70edd0d254dfa07f593c76effed94500847ccf8564c06",
+    "test/language/arguments-object/func-decl-args-trailing-comma-null.js": "80aecea8edd0d7bac1ddcfcd6cb97dc9a513b25a9283bb9cedd21fd77dd64d50",
+    "test/language/arguments-object/func-expr-args-trailing-comma-undefined.js": "cf39515a9031db4c81db231a157516bdc97617c392e4ef28890b2ae74777a99e",
     "test/language/expressions/addition/S11.6.1_A4_T1.js": "12928eb319dcf0cc785e399580effb0b7495709296dce9c0a58e8408616a959f",
     "test/language/expressions/addition/S11.6.1_A4_T2.js": "aee914241b607f56a98de04492f2d580e7bc69cca232af679d0c02b7025cc06b",
     "test/language/expressions/addition/S11.6.1_A4_T3.js": "987b1c3cf66b6bbb2f6d8aaf6d1435cb1238b19132fa861a91aa2c35085d229d",

tests/test262/vendor/test/language/arguments-object/func-decl-args-trailing-comma-null.js

@@ -0,0 +1,43 @@
+// This file was procedurally generated from the following sources:
+// - src/arguments/args-trailing-comma-null.case
+// - src/arguments/default/func-decl.template
+/*---
+description: A trailing comma after null should not increase the arguments.length (function declaration)
+esid: sec-arguments-exotic-objects
+flags: [generated]
+info: |
+    9.4.4 Arguments Exotic Objects
+
+    Most ECMAScript functions make an arguments object available to their code. Depending upon the
+    characteristics of the function definition, its arguments object is either an ordinary object
+    or an arguments exotic object.
+
+    Trailing comma in the arguments list
+
+    Left-Hand-Side Expressions
+
+    Arguments :
+        ( )
+        ( ArgumentList )
+        ( ArgumentList , )
+
+    ArgumentList :
+        AssignmentExpression
+        ... AssignmentExpression
+        ArgumentList , AssignmentExpression
+        ArgumentList , ... AssignmentExpression
+---*/
+
+
+var callCount = 0;
+// Stores a reference `ref` for case evaluation
+function ref() {
+  assert.sameValue(arguments.length, 2);
+  assert.sameValue(arguments[0], 42);
+  assert.sameValue(arguments[1], null);
+  callCount = callCount + 1;
+}
+
+ref(42, null,);
+
+assert.sameValue(callCount, 1, 'function invoked exactly once');

tests/test262/vendor/test/language/arguments-object/func-expr-args-trailing-comma-undefined.js

@@ -0,0 +1,44 @@
+// This file was procedurally generated from the following sources:
+// - src/arguments/args-trailing-comma-undefined.case
+// - src/arguments/default/func-expr.template
+/*---
+description: A trailing comma after undefined should not increase the arguments.length (function expression)
+esid: sec-arguments-exotic-objects
+flags: [generated]
+info: |
+    9.4.4 Arguments Exotic Objects
+
+    Most ECMAScript functions make an arguments object available to their code. Depending upon the
+    characteristics of the function definition, its arguments object is either an ordinary object
+    or an arguments exotic object.
+
+    Trailing comma in the arguments list
+
+    Left-Hand-Side Expressions
+
+    Arguments :
+        ( )
+        ( ArgumentList )
+        ( ArgumentList , )
+
+    ArgumentList :
+        AssignmentExpression
+        ... AssignmentExpression
+        ArgumentList , AssignmentExpression
+        ArgumentList , ... AssignmentExpression
+---*/
+
+
+var callCount = 0;
+// Stores a reference `ref` for case evaluation
+var ref;
+ref = function() {
+  assert.sameValue(arguments.length, 2);
+  assert.sameValue(arguments[0], 42);
+  assert.sameValue(arguments[1], undefined);
+  callCount = callCount + 1;
+};
+
+ref(42, undefined,);
+
+assert.sameValue(callCount, 1, 'function invoked exactly once');