While converting flexbox layout to use logical coords, I'm hitting cases where we'll need some special-case handling for baseline computations. (e.g. if the flex container has a LTR writing-mode but its parent has a vertical writing-mode, then IIRC we need to use its horizontal center as the "baseline", regardless of what it thinks its LTR baseline is. And baseline-alignment of flex items will be different in a vertical-writing-mode flex container, as well.) To allow general flex-layout logicalization bugs to proceed (& mostly convert between physical & logical types), without having to handle baseline special-cases up-front, I'm filing this bug as a placeholder where I can circle back and logicalize baseline-handling & add special-cases / child-to-parent conversions as-needed.
Created attachment 8756150 [details] testcase If I flip the axis using "flex-direction:column", shouldn't baseline alignment work for vertical items then? Or am I missing something here... it seems Chrome doesn't do baseline alignment either in this case so maybe I am. The spec language here seems to suggest it should work though: https://drafts.csswg.org/css-align-3/#baseline-align-self (I'm expecting the "a"'s to align their baselines.)
I believe your expectation is correct, yeah. Right now, I think our baseline-alignment code only works for "flex-direction:row", since (per this bug) it still needs tweaking to be writing-mode aware. (And in a traditional English LTR writing mode, "flex-direction:row" is the only case where baseline alignment of items makes sense.)