[Webkit-unassigned] [Bug 161002] New: Nested calculations using intermediate CSS Custom Properties don't work

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161002

            Bug ID: 161002
           Summary: Nested calculations using intermediate CSS Custom
                    Properties don't work
    Classification: Unclassified
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Macintosh
                OS: OS X 10.11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sgomes at google.com

As per example 9 in section 2.2 (Resolving Dependency Cycles) of the spec (https://drafts.csswg.org/css-variables/), it should be possible to have nested calculations:

one   { --foo: 10px; }
two   { --bar: calc(var(--foo) + 10px); }
three { --foo: calc(var(--bar) + 10px); }

This doesn't seem to work in Safari 9.1.2 or Safari Technology Preview.

Furthermore, it is stated: "Custom properties are left almost entirely unevaluated, except that they allow and evaluate the var() function in their value."
This implies that it should be possible to declare the intermediate calculations without calc() as well, as the value returned by var() would just be substituted into the new definition.

I have prepared a demo illustrating both ways of nesting calculations; one using calc() for the intermediate steps (as per the example above), and one using calc() for the final step only: http://codepen.io/anon/pen/bZJaVO
The expected result is that the third div in both groups is 30px wide.

Steps to reproduce:
1 - Load http://codepen.io/anon/pen/bZJaVO
2 - Observe third div in each group

Expected results: third div should be 30px wide.

Actual results: third div is 10px wide in Safari 9.1.2; third div fits to screen width in Safari Technology Preview.

Other browsers: The demo produces the expected result in both Chrome 53 and Firefox 48.

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