1357483 - Function#toString on a class prints more than it should

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Michał Gołębiowski-Owczarek [:mgol]]

The following code:

(class C {}) + ''

evaluates to:

"class C {})"

instead of the correct:

"class C {}"

This works fine in current Chrome, Safari & Edge.

The bug exists in latest Nightly, i.e. "55.0a1 (2017-04-18)".

Comment 1

[Shu-yu Guo [:shu]]

Oh goddammit.

Comment 2

[Shu-yu Guo [:shu]]

The bug is that for class expressions without constructors, the ClassNode's pn_pos holds the source offsets. For some reason, parsing parenthesized expressions sets the inner expression's end position to include the right paren, which is what manifests this bug.

I'm seeing what happens if we just... don't do that.

Comment 3

[Shu-yu Guo [:shu]]

Attachment: Stop changing the end position of parenthesized expression ParseNodes.

Comment 4

[Jeff Walden [:Waldo]]

Comment on attachment 8860221 [details] [diff] [review]
Stop changing the end position of parenthesized expression ParseNodes.

Review of attachment 8860221 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/tests/ecma_6/Class/parenExprToString.js
@@ +1,5 @@
> +// Test that parenthesized class expressions don't get their toString offsets
> +// messed up.
> +
> +assertEq((class {}) + '', "class {}");
> +assertEq(((class {})) + '', "class {}");

Might as well invoke .toString() directly on them for utmost clarity, no?

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/e064b7cde203
Stop changing the end position of parenthesized expression ParseNodes. (r=Waldo)

Comment 6

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/e064b7cde203