[grey-area]

As an everyday user of Go perplexed by this making it into the mainline, I'd like to second the request to make this feature optional. More documentation would be nice, but I'd prefer the default to change.

The assumptions in that v2 go modules article around the meaning of major semantic versions do not jibe with the way the majority of software in use today uses version numbers - they are most often used to denote new features, which may or may not have breaking changes large or small, and small breaking changes are tolerated all the time, often in minor versions. This assertion in particular seems wrong to me for most software in use today:

By definition, a new major version of a package is not backwards compatible with the previous version.

[deklerk]

Semver is very clear on what a minor vs a major change means.

> the majority of software in use today uses version numbers - they are most often used to denote new features, which may or may not have breaking changes large or small, and small breaking changes are tolerated all the time, often in minor versions

We're getting into opinion here. Let's be clear: semver very strictly, objectively disagrees with this approach. In general, this approach of "what's a few breaking changes in a minor release amongst friends" leads to terrible user experiences.

Go modules takes the cost of churn, which in some languages gets externalized to all users, and places it on the module author instead. That is far more scalable and results in much happier users, even though module authors sometimes have to be more careful or do more work.

[grey-area]

Thanks for working on the docs and engaging here, I know it can sometimes be a thankless task.

I don't think it's a matter of opinion that the vast majority of software in common use does not use strict semantic versioning, most likely including the web browser and operating system you are using to read this comment, popular packages like kubernetes, and the Go project itself in the mooted 2.0 with no breaking changes. It is highly desirable to avoid significant breakage, even to the point of ignoring strict semver and avoiding it across major version changes! So I'm not arguing for encouraging packages to break, but rather the reverse, I prefer the status quo pre go mod where packages are assumed not to break importers, though sometimes small breakage happens and/or is acceptable.

Most packages use a weaker version of semver than the one you describe, which is still useful, so I'm not clear why the go tools have to impose the very strong version which is not commonly used. The difficulties introduced seem to outweigh any benefit to me.

[timidger]

Because the version of web browser and the kernel more or less doesn't matter because they care way more about backwards compatibility than the "vast majority of software".

The kernel doesn't break user space. Web browsers' api generally remains backwards compatible (how long did it take to remove flash - and you can still install it if you want!)

[grey-area]

Prior to this change, all go software operated on this assumption (do not break users of the pkg), which doesn't comply with strict semver.

It worked fine.

[munificent]

You mention "major semantic versions", but semver itself explicitly says that the point of major version changes is backwards incompatibility.

> This assertion in particular seems wrong to me for most software in use today: By definition, a new major version of a package is not backwards compatible with the previous version.

It is true for any package manager using semver, cargo, npm, pub, etc.

[grey-area]

In practice, that is not true for many of the packages on those managers or even for the mooted Go 2.0. Major versions are often used for major feature releases or changes of direction, which may or may not break importers, minor versions sometimes break things. There is more chance of breakage in a major version but it's not a given. And that's ok.

The meaning of versions is a negotiation between producer and consumer, not a fixed rigid set of rules as strict semver would have you believe. In practice the definitions are more fluid, something like major: big changes, may be breakage, minor: minor changes, should be no or minimal breakage, patch: small fix, no breakage.

Putting versions in the import path is not something any of the popular package managers do AFAIK, and they certainly don't force you to do that, nor do they force you to use strict semantic versioning.

[munificent]

> There is more chance of breakage in a major version but it's not a given. And that's ok.

I think you have are looking at this from the perspective of the package consumer, but versioning is controlled by the package maintainer and its their notion of "breaking" that determines the versioning story.

Yes, many users of a package will in practice not be broken by a "breaking change". I could, for example, depend on your package but not actually call a single function in it. You could do whatever you want to the package without breaking me.

But the package maintainer does not have awareness of all of the actual users of their code. So to them, a "breaking change" means "could this change break some users". If the answer is yes, it is a breaking change.

> not a fixed rigid set of rules as strict semver would have you believe.

Semver is a guideline so is naturally somewhat idealistic. Yes, there are certainly edge cases where even a trivial change could technically break some users. (For example, users often inadvertently rely on timing characteristics of APIs, which means any performance chance for better or worse could break them.)

But, in general, if you're a package maintainer, your definition of "breaking change" means "is it possible that there exists a reasonable user of my API that will be broken by this?", not "is there actually some real code that is broken?" Package maintainers sort of live as if their code is being called by the quantum superposition of all possible API users and have to evolve their APIs accordingly. Package consumers live in a fully-collapsed wave function where they only care about their specific concrete code and the specific concrete package they use.

> Putting versions in the import path is not something any of the popular package managers do AFAIK, and they certainly don't force you to do that,

That's correct. Go is the odd one out.

> nor do they force you to use strict semantic versioning.

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.

Instead, this is a relationship between package consumers and maintainers. If a consumer assumes the package maintainer follows semver but the maintainer does not, the consumers are gonna have a bad time when they accidentally get a version of the package that breaks them. This is acutely painful when this happens deep inside some transitive dependency where none of the humans involved are aware of each other.

When consumers have a bad time, they tend to let package maintainers know, so there is a fairly strong effective social pressure to version your packages in a way that lets consumers reliably know what kind of version ranges are safe to use. Semver is just one enshrines consensus agreement on how to do that.

[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.