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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/266340">266340</a></dd>
<dt>Author</dt> <dd>ysuzuki@apple.com</dd>
<dt>Date</dt> <dd>2020-08-30 18:26:30 -0700 (Sun, 30 Aug 2020)</dd>
</dl>

<h3>Log Message</h3>
<pre>[JSC] async function cannot appear in single-statement context
https://bugs.webkit.org/show_bug.cgi?id=215993

Reviewed by Darin Adler.

JSTests:

* stress/async-function-lookahead.js: Added.
(testSyntax):
(testSyntaxError):
(testSyntax.false.async t):
(testSyntaxError.false.async t):
* test262/expectations.yaml:

Source/JavaScriptCore:

The following code is syntax error[1] because ExpressionStatement has `async [no LineTerminator here] function` lookahead.

    if (false)
        async function t() { }

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

* parser/Parser.cpp:
(JSC::Parser<LexerType>::parseStatement):
(JSC::Parser<LexerType>::maybeParseAsyncFunctionDeclarationStatement): Deleted.
* parser/Parser.h:</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkJSTestsChangeLog">trunk/JSTests/ChangeLog</a></li>
<li><a href="#trunkJSTeststest262expectationsyaml">trunk/JSTests/test262/expectations.yaml</a></li>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreparserParsercpp">trunk/Source/JavaScriptCore/parser/Parser.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreparserParserh">trunk/Source/JavaScriptCore/parser/Parser.h</a></li>
</ul>

<h3>Added Paths</h3>
<ul>
<li><a href="#trunkJSTestsstressasyncfunctionlookaheadjs">trunk/JSTests/stress/async-function-lookahead.js</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkJSTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/JSTests/ChangeLog (266339 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/ChangeLog  2020-08-31 01:20:48 UTC (rev 266339)
+++ trunk/JSTests/ChangeLog     2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -1,3 +1,17 @@
</span><ins>+2020-08-30  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] async function cannot appear in single-statement context
+        https://bugs.webkit.org/show_bug.cgi?id=215993
+
+        Reviewed by Darin Adler.
+
+        * stress/async-function-lookahead.js: Added.
+        (testSyntax):
+        (testSyntaxError):
+        (testSyntax.false.async t):
+        (testSyntaxError.false.async t):
+        * test262/expectations.yaml:
+
</ins><span class="cx"> 2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
</span><span class="cx"> 
</span><span class="cx">         [JSC] `let [` sequence cannot appear in ExpressionStatement context
</span></span></pre></div>
<a id="trunkJSTestsstressasyncfunctionlookaheadjs"></a>
<div class="addfile"><h4>Added: trunk/JSTests/stress/async-function-lookahead.js (0 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/stress/async-function-lookahead.js                         (rev 0)
+++ trunk/JSTests/stress/async-function-lookahead.js    2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -0,0 +1,33 @@
</span><ins>+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));
+}
+
+testSyntax(`
+if (false)
+    async
+function t() { }
+`);
+
+testSyntaxError(`
+if (false)
+    async function t() { }
+`, `SyntaxError: Unexpected keyword 'function'. Cannot use async function declaration in single-statement context.`);
</ins></span></pre></div>
<a id="trunkJSTeststest262expectationsyaml"></a>
<div class="modfile"><h4>Modified: trunk/JSTests/test262/expectations.yaml (266339 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/test262/expectations.yaml  2020-08-31 01:20:48 UTC (rev 266339)
+++ trunk/JSTests/test262/expectations.yaml     2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -3197,18 +3197,6 @@
</span><span class="cx">   default: 'Test262Error: Expected a SyntaxError to be thrown but no exception was thrown at all'
</span><span class="cx"> test/language/statements/generators/scope-param-rest-elem-var-open.js:
</span><span class="cx">   default: 'Test262Error: Expected SameValue(«outside», «inside») to be true'
</span><del>-test/language/statements/if/if-async-fun-else-async-fun.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-async-fun-else-stmt.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-async-fun-no-else.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-async-gen-else-async-gen.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-async-gen-else-stmt.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-async-gen-no-else.js:
-  default: 'Test262: This statement should not be evaluated.'
</del><span class="cx"> test/language/statements/if/if-gen-else-gen.js:
</span><span class="cx">   default: 'Test262: This statement should not be evaluated.'
</span><span class="cx"> test/language/statements/if/if-gen-else-stmt.js:
</span><span class="lines">@@ -3215,10 +3203,6 @@
</span><span class="cx">   default: 'Test262: This statement should not be evaluated.'
</span><span class="cx"> test/language/statements/if/if-gen-no-else.js:
</span><span class="cx">   default: 'Test262: This statement should not be evaluated.'
</span><del>-test/language/statements/if/if-stmt-else-async-fun.js:
-  default: 'Test262: This statement should not be evaluated.'
-test/language/statements/if/if-stmt-else-async-gen.js:
-  default: 'Test262: This statement should not be evaluated.'
</del><span class="cx"> test/language/statements/if/if-stmt-else-gen.js:
</span><span class="cx">   default: 'Test262: This statement should not be evaluated.'
</span><span class="cx"> test/language/statements/labeled/decl-async-function.js:
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (266339 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog    2020-08-31 01:20:48 UTC (rev 266339)
+++ trunk/Source/JavaScriptCore/ChangeLog       2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -1,3 +1,22 @@
</span><ins>+2020-08-30  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] async function cannot appear in single-statement context
+        https://bugs.webkit.org/show_bug.cgi?id=215993
+
+        Reviewed by Darin Adler.
+
+        The following code is syntax error[1] because ExpressionStatement has `async [no LineTerminator here] function` lookahead.
+
+            if (false)
+                async function t() { }
+
+        [1]: https://tc39.es/ecma262/#sec-expression-statement
+
+        * parser/Parser.cpp:
+        (JSC::Parser<LexerType>::parseStatement):
+        (JSC::Parser<LexerType>::maybeParseAsyncFunctionDeclarationStatement): Deleted.
+        * parser/Parser.h:
+
</ins><span class="cx"> 2020-08-29  Yusuke Suzuki  <ysuzuki@apple.com>
</span><span class="cx"> 
</span><span class="cx">         [JSC] `let [` sequence cannot appear in ExpressionStatement context
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreparserParsercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/parser/Parser.cpp (266339 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/parser/Parser.cpp    2020-08-31 01:20:48 UTC (rev 266339)
+++ trunk/Source/JavaScriptCore/parser/Parser.cpp       2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -1982,8 +1982,10 @@
</span><span class="cx">     }
</span><span class="cx">     case IDENT:
</span><span class="cx">         if (UNLIKELY(*m_token.m_data.ident == m_vm.propertyNames->async && !m_token.m_data.escaped)) {
</span><del>-            if (maybeParseAsyncFunctionDeclarationStatement(context, result, parentAllowsFunctionDeclarationAsStatement))
-                break;
</del><ins>+            SavePoint savePoint = createSavePoint(context);
+            next();
+            failIfTrue(match(FUNCTION) && !m_lexer->hasLineTerminatorBeforeToken(), "Cannot use async function declaration in single-statement context");
+            restoreSavePoint(context, savePoint);
</ins><span class="cx">         }
</span><span class="cx">         FALLTHROUGH;
</span><span class="cx">     case AWAIT:
</span><span class="lines">@@ -2068,21 +2070,6 @@
</span><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> template <typename LexerType>
</span><del>-template <class TreeBuilder> bool Parser<LexerType>::maybeParseAsyncFunctionDeclarationStatement(TreeBuilder& context, TreeStatement& result, bool parentAllowsFunctionDeclarationAsStatement)
-{
-    ASSERT(matchContextualKeyword(m_vm.propertyNames->async));
-    SavePoint savePoint = createSavePoint(context);
-    next();
-    if (match(FUNCTION) && !m_lexer->hasLineTerminatorBeforeToken()) {
-        const bool isAsync = true;
-        result = parseFunctionDeclarationStatement(context, isAsync, parentAllowsFunctionDeclarationAsStatement);
-        return true;
-    }
-    restoreSavePoint(context, savePoint);
-    return false;
-}
-
-template <typename LexerType>
</del><span class="cx"> template <class TreeBuilder> bool Parser<LexerType>::parseFormalParameters(TreeBuilder& context, TreeFormalParameterList list, bool isArrowFunction, bool isMethod, unsigned& parameterCount)
</span><span class="cx"> {
</span><span class="cx"> #define failIfDuplicateIfViolation() \
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreparserParserh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/parser/Parser.h (266339 => 266340)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/parser/Parser.h      2020-08-31 01:20:48 UTC (rev 266339)
+++ trunk/Source/JavaScriptCore/parser/Parser.h 2020-08-31 01:26:30 UTC (rev 266340)
</span><span class="lines">@@ -1720,7 +1720,6 @@
</span><span class="cx">     template <class TreeBuilder> TreeStatement parseFunctionDeclaration(TreeBuilder&, ExportType = ExportType::NotExported, DeclarationDefaultContext = DeclarationDefaultContext::Standard, Optional<int> functionConstructorParametersEndPosition = WTF::nullopt);
</span><span class="cx">     template <class TreeBuilder> TreeStatement parseFunctionDeclarationStatement(TreeBuilder&, bool isAsync, bool parentAllowsFunctionDeclarationAsStatement);
</span><span class="cx">     template <class TreeBuilder> TreeStatement parseAsyncFunctionDeclaration(TreeBuilder&, ExportType = ExportType::NotExported, DeclarationDefaultContext = DeclarationDefaultContext::Standard, Optional<int> functionConstructorParametersEndPosition = WTF::nullopt);
</span><del>-    template <class TreeBuilder> NEVER_INLINE bool maybeParseAsyncFunctionDeclarationStatement(TreeBuilder& context, TreeStatement& result, bool parentAllowsFunctionDeclarationAsStatement);
</del><span class="cx">     template <class TreeBuilder> TreeStatement parseVariableDeclaration(TreeBuilder&, DeclarationType, ExportType = ExportType::NotExported);
</span><span class="cx">     template <class TreeBuilder> TreeStatement parseDoWhileStatement(TreeBuilder&);
</span><span class="cx">     template <class TreeBuilder> TreeStatement parseWhileStatement(TreeBuilder&);
</span></span></pre>
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