Bug 123506 – JavaScript parser bug

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Mihai Bazon]

// fails with SyntaxError: Expected token ')'
( function(){ return this || eval('this'); }().x = "y" );

// fails with SyntaxError: Unexpected token '='
1, function(){ return this || eval('this'); }().x = "y";

//// weird that we get different error messages

//// The following all work.

// place the function call inside parens
( (function(){ return this || eval('this'); }()).x = "y" );
1, (function(){ return this || eval('this'); }()).x = "y";

// simplify the return expression, keep `then`
( function(){ return this; }().x = "y" );
1, function(){ return this; }().x = "y";

// keep `eval`
( function(){ return eval('this'); }().x = "y" );
1, function(){ return eval('this'); }().x = "y";

// place the return expression inside parens (!!)
( function(){ return ( this || eval('this') ); }().x = "y" );
1, function(){ return ( this || eval('this') ); }().x = "y";

[Radar WebKit Bug Importer]

<rdar://problem/15362517>

[Oliver Hunt]

Alas shipping safari has really broken error messages, trunk is much much better.  I suspect that the problem here is that we're not correctly resetting state after we finish parsing the function body

[Oliver Hunt]

(In reply to comment #0)
> // fails with SyntaxError: Expected token ')'
> ( function(){ return this || eval('this'); }().x = "y" );
This is incorrectly propagating parser state out of the function body.

> 
> // fails with SyntaxError: Unexpected token '='
> 1, function(){ return this || eval('this'); }().x = "y";

This is a correct failure.  The error message is just really bad

[Oliver Hunt]

Created attachment 215716 [details]
Patch

[Mark Lam]

Comment on attachment 215716 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=215716&action=review

r=me with the spaces clean up.

> Source/JavaScriptCore/parser/Parser.h:404
> -
> +    

Remove these blank spaces.

[Oliver Hunt]

Committed r158425: <http://trac.webkit.org/changeset/158425>

[Mihai Bazon]

>> // fails with SyntaxError: Unexpected token '='
>> 1, function(){ return this || eval('this'); }().x = "y";

> This is a correct failure.  The error message is just really bad

Nope, it's valid code.  It's just the assignment from the first line, in a sequence expression.  All other engines parse it correctly, also JS-based parsers (UglifyJS [1], Acorn [2] and Esprima [3]).

[1] https://github.com/mishoo/UglifyJS2
[2] https://github.com/marijnh/acorn
[3] http://esprima.org/

[Oliver Hunt]

(In reply to comment #7)
> >> // fails with SyntaxError: Unexpected token '='
> >> 1, function(){ return this || eval('this'); }().x = "y";
> 
> > This is a correct failure.  The error message is just really bad
> 

Oh, whoops i missed the 1, at the beginning (i interpreted it as an enumerated list) anyhow, both cases are fixed