1454069 - [css-flexbox] Ensure we treat used "flex-basis:<percentage>" like flex-basis:content when flex container has indefinite size

Status: ASSIGNED

(Core :: Layout, enhancement, P3)

Description

[Daniel Holbert [:dholbert]]

Per https://drafts.csswg.org/css-flexbox-1/#valdef-flex-basis-auto :

# ...percentage values of flex-basis are resolved against
# the flex item’s containing block (i.e. its flex
# container); and if that containing block’s size is
# indefinite, the used value for 'flex-basis' is 'content'.
https://drafts.csswg.org/css-flexbox-1/#propdef-flex-basis

I'm filing this to be sure that this is how we actually behave for these indefinite-CB-with-percent-[used]-flex-basis scenarios.  A quick local test suggests that we do.  We should add a reftest (or a few) for this, too.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: testcase 1

Here's an initial testcase, using "flex-basis: auto" and a percent height.

The flex items here all have a teal border, and the fact that they shrinkwrap their content-height is a sign that we're doing the right thing.