Auto merge of #59651 - tmandry:discr-index, r=eddyb

 Add discr_index to multi-variant layouts

We remove the assumption that the discriminant is always field 0, in
preparations for layouts like generators where this is not (always) going to be
the case.

Specifically, upvars are going to go before the discriminant. In theory, it's possible to remove _that_ assumption instead and keep the discriminant at field index 0, but one assumption or the other had to go :)

There is one place I know of in the debuginfo code where we'll still need to remove assumptions that the discriminant is the _only_ field. I was planning on doing this along with the upcoming generator change, which will also include tests that exercise the code changing in this PR.

r? @eddyb
cc @oli-obk
cc @cramertj

0 files changed, 0 insertions, 0 deletions