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Michael Goulet
40a781b179
Ignore but do not assume region obligations from unifying headers in negative coherence Partly addresses a FIXME that was added in #112875. Just as we can throw away the nested trait/projection obligations from unifying two impl headers, we can also just throw away the region obligations too. I removed part of the FIXME that was incorrect, namely: > Given that the only region constraints we get are involving inference regions in the root, it shouldn't matter, but still sus. This is not true when unifying `fn(A)` and `for<'b> fn(&'b B)` which ends up with placeholder region outlives from non-root universes. I'm pretty sure this is okay, though it would be nice if we were to use them as assumptions. See the `explicit` revision of the test I committed, which still fails. Fixes #117986 r? lcnr, feel free to reassign tho.