See attached testcase (with a vertical-enabled build). The size of the two red-bordered inner <div>s can be varied with the slider; the text within them is expected to re-wrap accordingly. In horizontal mode, all is well. When writing-mode is set to vertical, note how the right-hand <div>, which contains a <p> rather than simply containing the text directly, does not wrap correctly to its containing <div>; its line-breaking stays unchanged. Specifically, it looks like the <p> is wrapping its line *height* (inline-size) to the *width* of the green-bordered outer <div>, instead of to the height of its immediate container.

And here's the testcase I meant to attach.

The second hunk is the one that fixes the bug, but while I was there I checked other callers of ComputeSize and found the one in the first hunk as well.

Comment on attachment 8508086 [details] [diff] [review] Patch: pass inline size, not width, to ComputeSize Review of attachment 8508086 [details] [diff] [review]: ----------------------------------------------------------------- LGTM, thanks!

https://hg.mozilla.org/integration/mozilla-inbound/rev/62c88e2cdf48 https://hg.mozilla.org/integration/mozilla-inbound/rev/335a39df0c79

https://hg.mozilla.org/mozilla-central/rev/62c88e2cdf48 https://hg.mozilla.org/mozilla-central/rev/335a39df0c79