Unfortunately Rust is not actually using semver, which I always found confusing because they seem to be in support of it, and they even include a semver library in the core distribution. If they were following semver, this release would be version 0.10.0 (notice the patch version).
The point of semver is to stick to a standard, instead of every project deviating from common practice in subtly incompatible ways.
Right, we didn't really "adopt" semantic versioning until sometime after 0.1, and so we've never really gotten into the habit of including the patch revision (and with one exception, we've never issued a patch for any of our unstable releases anyway).
The point of semver is to stick to a standard, instead of every project deviating from common practice in subtly incompatible ways.