Re: Go importer and packages with version flags

[Sarah Morgensen]

Hi Katherine, Jack,

Katherine Cox-Buday <cox.katherine.e@gmail.com> writes:

> Jack Hill <jackhill@jackhill.us> writes:
>
>> Hi Guix,
>
> Hey, Jack, a few thoughts.
>
>> While I was was working with the go importer today, it suggested I package
>> go-github-com-russross-blackfriday-v2. Fair enough, except we already have a
>> package for go-github-com-russross-blackfriday.
>
> I was poking around a rust code-base the other day and I noticed our crate
> importer, and thus a lot of crate packages, have major-version suffixes. I
> think one of the unique benefits of Guix is that it can simultaneously have
> multiple versions of libraries installed, and I think we should allow this
> for library packages.
>
> I know that leads to dependency graph explosion, but perhaps we only commit
> to substitutes for the latest version, and thus any packages using old
> versions. It should converge over time unless packages go unmaintained.
>
> I thought our current stance was to only allow one version at a time, but
> the crate packages made me question this. I'd like clarity too.

I think there's a bit of a difference between (our packages for) the Rust and
Go ecosystems here.

In the Go ecosystem, a module is uniquely identified by its module path,
e.g. "github.com/russross/blackfriday/v2".  According to Go's major version
suffix rules [0], "[s]tarting with major version 2, module paths must have a
major version suffix like /v2 that matches the major version."  Therefore,
each major version is logically a different module according to Go, and so I
think we should treat them as separate packages as well.  (Note that in many
cases we can use 'inherit' for brevity.)

Additionally, the major version suffix rules dictate that "[i]f an old package
and a new package have the same import path, the new package must be backwards
compatible with the old package."  Assuming upstream sources follow the rules,
we should be able to update each Go package within each major version without
breaking dependencies.

(A corollary to that is that packages often break if you try to use a v2 when
it is expecting a v1.)

I think this differs from Rust, where we have, for example, package-0.1 and
package-0.2 coexisting.  This difference should prevent dependency graph
explosion for Go.

There are some caveats with "major version suffixes":

* Major versions 0 and 1 don't get a version suffix (so no /v1)...

    * ...except for module paths starting with "gopkg.in/", which always have
      a major version suffix, but theirs is styled ".v1" rather than "/v1".

* Modules may either be located in the repository root, or in a "/v2"
  subdirectory (for major version 2).  This makes things difficult for our
  importer, because we can't know whether the unpack path should include "/v2"
  without looking at the repository contents.

This is why Jack had to manually add "/v2" to the unpack path.  I recently
made some changes to the importer to better handle, for example,
"github.com/example/repository/subproject", but it doesn't yet discriminate
between "/subproject" and "/v2", so it treated "/v2" like a subdirectory of
the repository.  (Until we fix this properly, the importer should probably not
count major version suffixes when calculating the unpack path, since most
projects don't use a "/v2" subdirectory.)


All that to say... I think we should definitely maintain coexisting Go v2, v3,
etc. package definitions.  We should probably go the way of Rust though, so we
have them all in the same package, at different versions:

(define-public go-github-com-russross-blackfriday-v2
  (package
    (name "go-github-com-russross-blackfriday")
    (version "2.1.0")

instead of as different packages:

(define-public "go-github-com-russross-blackfriday-v2"
  (package
    (name "go-github-com-russross-blackfriday-v2")
    (version "2.1.0")

And of course, it should be policy to remove dependency packages with no
dependents.  (Perhaps we could write a new linter to warn if a "go-" package
has no inheriters and no dependents?)

Does that sound reasonable?

--
Sarah