[JSC] let [ sequence cannot appear in ExpressionStatement context

https://bugs.webkit.org/show_bug.cgi?id=215977

Reviewed by Ross Kirsling.

JSTests:

* stress/let-and-open-bracket.js: Added.
(testSyntax):
(testSyntaxError):
* test262/expectations.yaml:

Source/JavaScriptCore:

Because of ambiguity between destructuring assignment and member access (let IDENTIFIER), ECMA262 does not allow `let [` sequence in ExpressionStatement context[1].
We should throw SyntaxError when we see something like this.

    if (false)
        let [ok] = [42];

[1]: https://tc39.es/ecma262/#sec-expression-statement

* parser/Parser.cpp:
(JSC::Parser<LexerType>::parseStatement):

Canonical link: https://commits.webkit.org/228763@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@266327 268f45cc-cd09-0410-ab3c-d52691b4dbfc

JSTests/ChangeLog

@@ -1,3 +1,15 @@
+2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] `let [` sequence cannot appear in ExpressionStatement context
+        https://bugs.webkit.org/show_bug.cgi?id=215977
+
+        Reviewed by Ross Kirsling.
+
+        * stress/let-and-open-bracket.js: Added.
+        (testSyntax):
+        (testSyntaxError):
+        * test262/expectations.yaml:
+
 2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
 
         [JSC] for-of uses AssignmentExpression while for-in uses Expression

JSTests/stress/let-and-open-bracket.js

@@ -0,0 +1,37 @@
+function testSyntax(script) {
+    try {
+        eval(script);
+    } catch (error) {
+        if (error instanceof SyntaxError)
+            throw new Error("Bad error: " + String(error));
+    }
+}
+
+function testSyntaxError(script, message) {
+    var error = null;
+    try {
+        eval(script);
+    } catch (e) {
+        error = e;
+    }
+    if (!error)
+        throw new Error("Expected syntax error not thrown");
+
+    if (String(error) !== message)
+        throw new Error("Bad error: " + String(error));
+}
+
+testSyntaxError(`
+if (false) let [ok] = 40;
+`, `SyntaxError: Unexpected token '['. Cannot use lexical declaration in single-statement context.`);
+
+testSyntaxError(`
+if (false) let
+[ok] = 40;
+`, `SyntaxError: Unexpected token '['. Cannot use lexical declaration in single-statement context.`);
+
+testSyntax(`
+if (false) {
+    let [ok] = 40;
+}
+`);

JSTests/test262/expectations.yaml

@@ -3053,13 +3053,9 @@ test/language/statements/const/dstr/ary-ptrn-elem-id-iter-val-array-prototype.js
 test/language/statements/const/dstr/ary-ptrn-rest-id-direct.js:
   default: 'Test262Error: Expected true but got false'
   strict mode: 'Test262Error: Expected true but got false'
-test/language/statements/do-while/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/for-await-of/async-from-sync-iterator-continuation-abrupt-completion-get-constructor.js:
   default: 'Test262:AsyncTestFailure:Test262Error: Test262Error: Expected [start, tick 1, tick 2] and [start, tick 1, tick 2, catch] to have the same contents. '
   strict mode: 'Test262:AsyncTestFailure:Test262Error: Test262Error: Expected [start, tick 1, tick 2] and [start, tick 1, tick 2, catch] to have the same contents. '
-test/language/statements/for-await-of/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/for-await-of/ticks-with-async-iter-resolved-promise-and-constructor-lookup-two.js:
   default: 'Test262:AsyncTestFailure:Test262Error: Test262Error: Expected [pre, tick 1, tick 2, loop] and [pre, constructor, tick 1, loop, constructor, tick 2, post] to have the same contents. Ticks and constructor lookups'
   strict mode: 'Test262:AsyncTestFailure:Test262Error: Test262Error: Expected [pre, tick 1, tick 2, loop] and [pre, constructor, tick 1, loop, constructor, tick 2, post] to have the same contents. Ticks and constructor lookups'
@@ -3073,8 +3069,6 @@ test/language/statements/for-in/head-lhs-let.js:
   default: "SyntaxError: Cannot use the keyword 'in' as a lexical variable name."
 test/language/statements/for-in/identifier-let-allowed-as-lefthandside-expression-not-strict.js:
   default: "SyntaxError: Cannot use the keyword 'in' as a lexical variable name."
-test/language/statements/for-in/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/for-in/order-enumerable-shadowed.js:
   default: 'Test262Error: Expected [p1, p2] and [p1] to have the same contents. '
   strict mode: 'Test262Error: Expected [p1, p2] and [p1] to have the same contents. '
@@ -3156,8 +3150,6 @@ test/language/statements/for-of/dstr/obj-id-put-const.js:
 test/language/statements/for-of/dstr/obj-id-put-let.js:
   default: 'Test262Error: Expected a ReferenceError to be thrown but no exception was thrown at all'
   strict mode: 'Test262Error: Expected a ReferenceError to be thrown but no exception was thrown at all'
-test/language/statements/for-of/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/for/dstr/const-ary-init-iter-get-err-array-prototype.js:
   default: 'Test262Error: Expected a TypeError to be thrown but no exception was thrown at all'
   strict mode: 'Test262Error: Expected a TypeError to be thrown but no exception was thrown at all'
@@ -3187,8 +3179,6 @@ test/language/statements/for/dstr/var-ary-ptrn-rest-id-direct.js:
   strict mode: 'Test262Error: Expected true but got false'
 test/language/statements/for/head-lhs-let.js:
   default: "SyntaxError: Unexpected token ';'. Expected a parameter pattern or a ')' in parameter list."
-test/language/statements/for/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/for/scope-body-lex-open.js:
   default: 'Test262Error: Expected SameValue(«inside», «outside») to be true'
   strict mode: 'Test262Error: Expected SameValue(«inside», «outside») to be true'
@@ -3231,8 +3221,6 @@ test/language/statements/if/if-stmt-else-async-gen.js:
   default: 'Test262: This statement should not be evaluated.'
 test/language/statements/if/if-stmt-else-gen.js:
   default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/statements/labeled/decl-async-function.js:
   default: 'Test262: This statement should not be evaluated.'
   strict mode: 'Test262: This statement should not be evaluated.'
@@ -3368,10 +3356,6 @@ test/language/statements/variable/dstr/ary-ptrn-elem-id-iter-val-array-prototype
 test/language/statements/variable/dstr/ary-ptrn-rest-id-direct.js:
   default: 'Test262Error: Expected true but got false'
   strict mode: 'Test262Error: Expected true but got false'
-test/language/statements/while/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/with/let-array-with-newline.js:
-  default: 'Test262: This statement should not be evaluated.'
 test/language/types/reference/put-value-prop-base-primitive-realm.js:
   default: 'Test262Error: number Expected SameValue(«0», «1») to be true'
   strict mode: 'Test262Error: number Expected SameValue(«0», «1») to be true'

Source/JavaScriptCore/ChangeLog

@@ -1,3 +1,21 @@
+2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] `let [` sequence cannot appear in ExpressionStatement context
+        https://bugs.webkit.org/show_bug.cgi?id=215977
+
+        Reviewed by Ross Kirsling.
+
+        Because of ambiguity between destructuring assignment and member access (let IDENTIFIER), ECMA262 does not allow `let [` sequence in ExpressionStatement context[1].
+        We should throw SyntaxError when we see something like this.
+
+            if (false)
+                let [ok] = [42];
+
+        [1]: https://tc39.es/ecma262/#sec-expression-statement
+
+        * parser/Parser.cpp:
+        (JSC::Parser<LexerType>::parseStatement):
+
 2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
 
         [JSC] for-of uses AssignmentExpression while for-in uses Expression

Source/JavaScriptCore/parser/Parser.cpp

@@ -1970,6 +1970,12 @@ template <class TreeBuilder> TreeStatement Parser<LexerType>::parseStatement(Tre
         // These tokens imply the end of a set of source elements
         return 0;
     case LET: {
+        // https://tc39.es/ecma262/#sec-expression-statement
+        // ExpressionStatement's lookahead includes `let [` sequence.
+        SavePoint savePoint = createSavePoint(context);
+        next();
+        failIfTrue(match(OPENBRACKET), "Cannot use lexical declaration in single-statement context");
+        restoreSavePoint(context, savePoint);
         if (!strictMode())
             goto identcase;
         goto defaultCase;