461110 - Extra parens in decompilation of "a += b = 3"

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jesse Ruderman]

js> (function() { a += b = 3 })
function () {
    a += (b = 3);
}

Comment 1

[Jesse Ruderman]

This can happen with operators other than = on the right, such as instanceof.

Comment 2

[Benjamin Smedberg]

Why is this bad? It makes it clearer.

Comment 3

[Brendan Eich [:brendan]]

It's different, so expected output in testsuites and tools will need to be updated. It's not mandatory per the C-based operator precedence. And clearer mileage varies -- we wouldn't have changed this just to make it clearer by some lights.

I'm most interested in why it pops out of the precedence-based decompiler. If it is a natural consequence that would take particularly ugly, or just too much, extra code to fix, then it can stay. Jason, is the + in += messing things up?

/be

Comment 4

[Jason Orendorff [:jorendorff]]

Attachment: v1

Comment 5

[Brendan Eich [:brendan]]

Comment on attachment 344323 [details] [diff] [review]
v1

I should have seen this -- this patch improves things even if it adds lines of code, since it reduces the complexity in the POP_STR_PREC calls.

/be

Comment 6

[Jason Orendorff [:jorendorff]]

http://hg.mozilla.org/tracemonkey/rev/5203db613b10

Comment 7

[Bob Clary [:bc] (inactive)]

http://hg.mozilla.org/mozilla-central/rev/37b3fdbb0f07
/cvsroot/mozilla/js/tests/js1_5/decompilation/regress-461110.js,v  <--  regress-461110.js
initial revision: 1.1