1790303 - Make XUL have min-width/height: 0 by default.

Status: RESOLVED WONTFIX

(Core :: XUL, task)

Description

[Emilio Cobos Álvarez (:emilio)]

So that the minimum sizing that flexbox / grid has doesn't apply when emulating it.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1790303 - Harmonize min-height behavior across -moz-box and emulated flexbox. r=dholbert

UL boxes allow their children to shrink, so using min-sizes of zero
allow us to preserve that behavior when emulating -moz-box with flexbox.

This fixes some tests with emulated flexbox enabled
(tests that expect a <browser> to shrink under 150px for example).

To do this we need to revert an accidental change from bug 1527410.
Don't treat a min-height/width: 0 as "set" for XUL purposes. See the !=
0 here which is before that change:

https://searchfox.org/mozilla-central/rev/51aa53dc4e3194aa4cb105fdfd599bbec552c4f8/layout/xul/nsBox.cpp#509

This makes min-height discontinuous on XUL layout, but I think that's
fine, since XUL's behavior here is quite a mess already, and is the
pre-existing behavior anyways. Keep 0% for when you want "really zero"
behavior. Our front-end already had a few cases of that.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

XUL min-size is fairly different than flex min-size, but I think we can work with what we have here in practice.