alt Hacker NewsThe fundamental problem with Rust versioning is that 0.3.5 is compatible with 0.3.6, but not 0.4.0 or 1.0.0; when major version is 0, the minor takes the role of major and patch takes the role of minor. So packages iterate through 0.x versions, and eventually, they reach a version that's "stable".
If version 0.7 turned out to hit the right API and not require backward incompatible changes, releasing a version 1.0 would be as disruptive as a major version change to your users and communicate through version semantics that it is a breaking change.
Semver declares that version 0.x is for initial development where there is no stability guarantee at all. This is the right semantics for a versioning system, but Cargo doesn't follow this part of semver. Providing stability guarantees throughout the 0.x cycle inevitably results in projects getting stuck in 0.x.
This is one of my biggest gripes with Cargo. But Rust people seem to universally consider it a non-issue so I don't think it'll ever be fixed.
Replies
> If version 0.7 turned out to hit the right API and not require backward incompatible changes, releasing a version 1.0 would be as disruptive as a major version change
Nope, this is what the semver trick is for: https://github.com/dtolnay/semver-trick
TL;DR: You take the 0.7 library, release it as 1.0, then make a 0.7.1 release that does nothing other than depend on 1.0 and re-export all its items. Tada, a compatible 1.0 release that 0.7 users will get automatically when they upgrade.
Even more interesting is that you can use this to coordinate only partially-breaking changes, e.g. if you have 100 APIs in your library but only make a breaking change to one, you can re-export the 99 unbroken APIs and only end up making breaking changes in practice for users who actually use the one API with breaking changes.
The standard library has a whole bunch of tools to let them test and evolve APIs with a required-opt in, but every single ecosystem package has to get it right first try because Cargo will silently forcibly update packages and those evolution tools aren't available to third party packages.
Such a stupid state of affairs.
Personally, I think the 0 major version is a bad idea. I hear the desire to not want to have to make guarantees about stability in the early stages of development and you don't want people depending on it. But hiding that behind "v0.x" doesn't change the fact that you are releasing versions and people are depending on it.
If you didn't want people to depend on your package (hence the word "dependency") then why release it? If your public interface changes, bump that major version number. What are you afraid of? People taking your project seriously?
> The fundamental problem with Rust versioning is that 0.3.5 is compatible with 0.3.6, but not 0.4.0 or 1.0.0
That’s a feature of semver, not a bug :)
Long answer: You are right to notice that minor versions within a major release can introduce new APIs and changes but generally, should not break existing APIs until the next major release.
However, this rule only applies to libraries after they reach 1.0.0. Before 1.0.0, one shouldn’t expect any APIs to be frozen really.