cargo-semver-checks is the tooling you describe. It doesn't currently catch every possible semver violation, so it won't suggest version numbers for you yet, but that's the eventual goal!
Can you explain better what you want then? Because I understood your description as a tool that detects when a code change doesn't match semver versioning without a human having to annotate the changes as breaking or anything. And then shows what to correct.
Which is exactly what cargo-semver-checks does.
Like, the first line of the README after the name is "Lint your crate API changes for semver violations." - it quite specifically works with the actual crate API, not commit names, comments or any other human annotation.
It also will show you what broke semver and how, so you can fix it easily. And as the author stated, the goal is to suggest the correct version in the future.
You're right, the tool doesn't automatically generate the correct semver. If that's what you meant, it seems to have been lost in translation. Your first comment was "Just autodetect whatever you need". It says nothing about automatically generating the correct semver value.
