Rust core team has taken the approach of breakage without major version increments being acceptable as long as they deem the breakage "minor" (based on crates.io and companies they have close relationships to).
It is true that Rust, like all actively-maintained languages, can make changes that are theoretically breaking if all evidence strongly suggests that no code is actually going to break.
If I could go back and edit I would -- but it has been too long.