specs-go: make Version a string literal

[kolyshkin]

Version is initialized during package initialization, which happens on every start of any program importing this package (for example, runc, which re-executes itself on every container start and exec).

Using fmt.Sprintf for that takes about 4µs and 5 allocations (2920 bytes). Since VersionMajor, VersionMinor, VersionPatch and VersionDev are all constants, there is no need to compute Version at runtime at all, so make it a plain string literal (as suggested by @thaJeztah in review).

Version is kept as a variable rather than a constant, since some users overwrite it (e.g. kata-containers), and making it a constant would break them.

To make sure Version stays in sync with the constants, a test is added, and CI now runs go test. The release checklist in RELEASES.md is updated accordingly.

As a bonus, the package no longer imports fmt.

[AkihiroSuda]

Using fmt.Sprintf for that takes about 4µs and 5 allocations (2920 bytes).

Does it really matter?

[thaJeztah]

LGTM

[kolyshkin]

Using fmt.Sprintf for that takes about 4µs and 5 allocations (2920 bytes).

Does it really matter?

Ever so slightly 🤏🏻
For some reason printf-like functions are not very optimized in Go.

[thaJeztah]

For some reason printf-like functions are not very optimized in Go.

Yeah, there's perfsprint linter in golangci-lint, which flags various cases.

I think it's at least the parsing of the format-string that will always cause overhead, but I also have some recollection of trivial cases that stdlib probably could have a fast-path for, but didn't (which made me curious if there was some reason behind it, or just "nobody worked on improving it").

[thaJeztah]

To Akihiro's point;

Does it really matter?

It's definitely not critical, but (even more so if it becomes just a string); does it hurt? Also "no" I think?

I think this is part of @kolyshkin trip round code used to see "what more could we squeeze out of this", and I really enjoyed many of his discoveries. Some small, some more substantial, some I knew about, but also some that were interesting.

[thaJeztah]

LGTM