706091 - JS Correctness: Different output with/without options "-m -n -a" and generator

Status: RESOLVED DUPLICATE of bug 584594

(Core :: JavaScript Engine, defect)

Description

[Christian Holler (:decoder)]

The following test produces different output with/without options -m -n -a on mozilla-central revision e320f9f5536f:

test();
function test() {
    print("Hello world!");
    var g = (function() {
        try { 
            test("with({x: (c) = (x2 = [])})false;");
        } finally { yield 3; }
    })();
    g.next();
}


The amount of lines outputted differs depending on the CLI options (where $JS is just the javascript shell binary):

$ $JS -m -n  min.js | wc -l
67
$ $JS -m -n -a min.js | wc -l
55
$ $JS min.js | wc -l
80

Comment 1

[Brian Hackett [Laid off!]]

The stack is getting exhausted by this testcase, so the number of calls before the failure happens will vary depending on compilation options.  The stack overflow exception is generated, but ends up getting swallowed by the 'yield' inside the 'finally' block.

Comment 2

[Brian Hackett [Laid off!]]

Talked to dherman on IRC, and the generator behavior is correct here --- yielding with a pending exception suspends the current frame and doesn't post the exception until the generator resumes.  Since next() is only called on the generator once, the exception never gets posted.

Comment 3

[Dave Herman [:dherman]]

bhackett's comment looks right to me. This is just a difference of how many stack frames you can allocate before you get a stack overflow. The stack overflow exception is dropped because the generator is only advanced to yield in the finally block, but not resumed afterwards. Then all the outer frames just successfully complete the try-block and also yield from the finally block.

So net result: you get as many lines of output as there were test() stack frames before the overflow.

Dave