prevent quic-go from building on Go 1.17

[marten-seemann]

It looks like Go 1.17 won't introduce any changes to the structs for which we assert that they're identical between qtls and crypto/tls. That means that in principle, it would be possible to build quic-go using Go 1.17. We should prevent this, as users might expect Go 1.17 crypto/tls to take effect, which they don't as long as we don't create an updated qtls version.

cc @mvdan

The error message will look like this:

❯ go1.17 test
# github.com/lucas-clemente/quic-go/
internal/qtls/go117.go:3:1: expected 'package', found "quic-go doesn't build on Go 1.17 yet."

[codecov]

Codecov Report

Merging #3180 (b61e2fa) into master (0bc0e96) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3180   +/-   ##
=======================================
  Coverage   85.37%   85.37%           
=======================================
  Files         133      133           
  Lines        9819     9819           
=======================================
  Hits         8382     8382           
  Misses       1062     1062           
  Partials      375      375           

---

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[mvdan]

That's a clever way to give a useful compiler error - I'll be copying that :)

[marten-seemann]

That's a clever way to give a useful compiler error

Thanks. Actually, I was hoping that there is an even more direct way to print that error (without the expected 'package', found ...).