vet: check for "+build" comment inconsistently reports error in package doc

[kr]

What version of Go are you using (go version)?

go version go1.11beta2 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

What did you do?

https://play.golang.org/p/xABgz0L94ig

What did you expect to see?

No error message, as in https://play.golang.org/p/v6DLrueUHqN.

What did you see instead?

prog.go:5: +build comment must appear before package clause and be followed by a blank line

This makes it a little difficult to include example code in the package doc, when the example needs to show a build directive.

Note that it's not just interpreting the +build ignore as a build directive inside the package comment. If we alter that line so that line alone doesn't look like a Go comment, vet reports no error: https://play.golang.org/p/v6DLrueUHqN

[kr]

Oops, I think this is a duplicate of #26627.

[meirf]

@kr yea they look similar. I'm gonna close this, but please comment there if you feel the conversation/CLs in #26627 are not addressing your exact concerns.