802f72201d
cmse: improve error messages tracking issue: https://github.com/rust-lang/rust/issues/81391 tracking issue: https://github.com/rust-lang/rust/issues/75835 Improves the cmse error messages (e.g. by using more accurate spans), and attempts to clean up the control flow a bit. This is partially in preparation for one final addition: warnings when `union` types or types with niches cross the security boundary. That will be a folllow-up. Meant to be reviewed commit-by-commit r? ``@davidtwco``
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.