Bug 138839 – Web Inspector: Debugger should not mutate variable when hovering mouse over ++n expression

• Component: Web Inspector
• Status: RESOLVED FIXED

[Joseph Pecoraro]

* SUMMARY
When debugging javascript paused in the debugger, hovering over a line of the form ++n actually mutates the value of n. n++ does not have this behavior.

* TEST
<script type="text/javascript">
function test() {
    debugger;
    var n = 0;
    console.log(n);
    // Hover over next line. n shouldn't change
    n++;
    console.log(n);
    // Hover over next line. n changes but shouldn't
    ++n;
    console.log(n);
}
document.onload = test();
</script>

* STEPS TO REPRODUCE
1. Inspect test case
2. Reload or type test() into the console
3. Test hovering over n++ and see it doesn't mutate
4. Test hovering over ++n and see that it mutates n every time you hover over it

[Radar WebKit Bug Importer]

<rdar://problem/19018280>

[Joseph Pecoraro]

Created attachment 241796 [details]
[PATCH] Proposed Fix

[Joseph Pecoraro]

<rdar://problem/18995374>

[Timothy Hatcher]

Comment on attachment 241796 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=241796&action=review

> Source/WebInspectorUI/UserInterface/Controllers/CodeMirrorTokenTrackingController.js:490
> +            if (isExpression && token.string === "++")

What about --?

[Joseph Pecoraro]

(In reply to comment #4)
> Comment on attachment 241796 [details]
> [PATCH] Proposed Fix
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=241796&action=review
> 
> > Source/WebInspectorUI/UserInterface/Controllers/CodeMirrorTokenTrackingController.js:490
> > +            if (isExpression && token.string === "++")
> 
> What about --?

Doh! Tim also caught other operators, like:

    n+=n;

I'll put up another patch.

[Joseph Pecoraro]

Created attachment 241810 [details]
[PATCH] Proposed Fix

[Timothy Hatcher]

Comment on attachment 241810 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=241810&action=review

> Source/WebInspectorUI/UserInterface/Controllers/CodeMirrorTokenTrackingController.js:492
> +            // Disallow operators. We want the hovered expression to be just a single operand.
> +            // Also, some operators can modify values, such as pre-increment and assignment operators.
> +            if (isExpression && token.type.contains("operator"))
> +                break;

Nice!

[WebKit Commit Bot]

Comment on attachment 241810 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 241810

Committed r176325: <http://trac.webkit.org/changeset/176325>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.