1cf3dc6b5a
Rework unsizing coercions in the new solver Replaces https://github.com/rust-lang/rust/pull/141926, contains: - a commit adding tests that fail before this work - the two commits from the previous PR - a commit in which these tests are fixed - finally, a fixup for an in my opinion rather large regression in diagnostics. It's still not perfect, but better? I hope this is roughly what you had in mind Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/241 and https://github.com/rust-lang/trait-system-refactor-initiative/issues/238, adding tests for both r? ````@lcnr````