Follow-up to bug 1144096. Per the Grid spec, rows can grow during fragmentation: "3. If a grid area’s size changes due to fragmentation (do not include items that span rows in this decision), increase the grid row as necessary for rows that either: * have a content min track sizing function. * are in a grid that does not have an explicit height and the grid row is flexible. " https://drafts.csswg.org/css-grid/#fragmentation-alg Bug 1144096 implements that, but that step after the step that calculates the grid-template-rows/columns values that are cached for CSSOM.

Brad, I think this bug was fixed by your changes at some point, right? (i.e. we collect all values needed for the computed value properties and Grid API after the ReflowChildren() call)

Yes, barring a testcase that shows otherwise, it seems the code handles this correctly. ReflowChild called at https://dxr.mozilla.org/mozilla-central/source/layout/generic/nsGridContainerFrame.cpp#5731 and the building of the computed data happens shortly after at https://dxr.mozilla.org/mozilla-central/source/layout/generic/nsGridContainerFrame.cpp#5760.

OK, great.