1434658 - Update computed value of min-width:auto/min-height:auto per CSSWG resolution on Jan 31 2018

Status: RESOLVED FIXED

(Core :: Layout, enhancement, P3)

Description

[Daniel Holbert [:dholbert]]

The CSSWG resolved to change how min-width:auto/min-height:auto get resolved in their meeting today, and I'm pretty sure it's to do something different from what we do right now, but I'm not clear on what the resolved behavior is.  I asked for clarification:
 https://github.com/w3c/csswg-drafts/issues/2230#issuecomment-362010888

Hopefully there'll be some clarification soon though. In the meantime, I'm filing this bug as a placeholder.

Comment 1

[Daniel Holbert [:dholbert]]

OK, the CSSWG's resolution was:
> RESOLVED: compute min-width/min-height: auto to auto
...and fantasai clarified that this is for grid and flex items only.

(And elsewhere in the issue, it's implied that we should have auto compute to itself for *both* axes -- not just the main axis -- even though it only has a nontrivial effect in the main axis.  This is for simplicity & compatibility, since apparently this is what other engines already do.)

Comment 2

[Tantek Çelik]

CSSWG updated the minutes and resolution updated in issue 2230: https://github.com/w3c/csswg-drafts/issues/2230#issuecomment-362017226 tl;dr auto computed value is auto even if layout value is 0, for flex & grid items.

Comment 3

[Daniel Holbert [:dholbert]]

These "auto" values now live in the css-sizing spec, too, FWIW (no longer the flexbox spec).
  https://drafts.csswg.org/css-sizing/#propdef-min-width

Right now there's nothing there to say that "auto" would ever compute to anything other than itself!  But as a stepping stone, we probably want to keep it computing to "0" on non-flex/grid-items for now, at least for getComputedStyle purposes, because there may very well be legacy webcompat dependencies on that behavior.  And the previous spec text on this *required* it to resolve to 0 for non-flex[/grid]-items
> On a flex item whose overflow is visible in the main axis,
> when specified on the flex item’s main-axis min-size property,
> specifies an automatic minimum size. It otherwise computes to 0
> (unless otherwise defined by a future specification).

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: Bug 1434658: Simplify getComputedStyle behavior for "min-{width,height}:auto" to *always* return "auto" for flex/grid items, per CSSWG resolution.

This change is in response to this CSSWG resolution:
"RESOLVED: compute min-width/min-height: auto to auto"
https://github.com/w3c/csswg-drafts/issues/2230#issuecomment-362009042
...which was later clarified as only being applicable to grid/flex items (in
both axes). Other layout modes may get further min-width/min-height
clarification, but for now we'll leave that behavior the same (returning 0 from
getComputedStyle).

Review commit: https://reviewboard.mozilla.org/r/216954/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/216954/

Comment 5

[Brad Werth [:bradwerth]]

Comment on attachment 8947179 [details]
Bug 1434658: Simplify getComputedStyle behavior for "min-{width,height}:auto" to *always* return "auto" for flex/grid items, per CSSWG resolution.

https://reviewboard.mozilla.org/r/216954/#review222982

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/39ec8e1d686a
Simplify getComputedStyle behavior for "min-{width,height}:auto" to *always* return "auto" for flex/grid items, per CSSWG resolution. r=bradwerth

Comment 7

[Raul Gurzau (:RaulG)]

https://hg.mozilla.org/mozilla-central/rev/39ec8e1d686a