11780: feat: Add type mismatch diagnostic r=flodiebold a=flodiebold
This adds a proper diagnostic for type mismatches, turning "Add reference here", "Missing Ok or Some" and "Remove this semicolon" into quickfixes for this single diagnostic.
The diagnostic is marked as experimental when it does not have one of these quickfixes, so it can be turned off with `rust-analyzer.diagnostics.enableExperimental` (or specifically with `rust-analyzer.diagnostics.disabled` of course, the ID is `type-mismatch`).
There will still be some false positives, but I think there shouldn't be too many especially when the Chalk fix lands, and it's still experimental anyway 🙂
This also fixes type checking for `rustc_legacy_const_generics` just to avoid some errors in tests.
Co-authored-by: Florian Diebold <flodiebold@gmail.com>
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