[grey-area]

The package manager itself doesn't necessarily care if package maintainers strictly follow semantic versioning. The version resolution algorithm usually presumes packages do. But if they don't, the package manager don't care.

This was the core point I was trying to make - other package managers correctly leave this negotiation on how much breakage is acceptable to producers and consumers, they do not impose strict semver but a looser one, and importers choose how strict they want to be on tracking changes in their requirements file (go.mod or similar), while producers choose how strict they are going to be with their semver (strict semver is almost never used in its pure form for good reasons, versions communicate more than breaking changes).

The result of this change to go imposing strict semver on both parties will be IMO far more breaking changes, because it explicitly encourages them and forces importers to always choose a major version. It's a change of culture from previous go releases and will have significant impact on behaviour.

We'll also end up with a bifurcated ecosystem with producers who don't like the change staying on v1 and others breaking their packages all the time and leaving frustrated consumers behind on older versions without bug fixes.