I'm seeing this error when building a package that imports another package. It uses --tags, don't know if it is related somehow.

The error: https://pastebin.com/raw/5RSvSQF9
My versions:

fiatjaf@cantillon ~/c/g/s/g/f/summuladb> gopherjs version
GopherJS 1.8-1
fiatjaf@cantillon ~/c/g/s/g/f/summuladb> go version
go version go1.8 linux/amd64

To (try to) reproduce, download the code from https://github.com/fiatjaf/summuladb/tree/ca927b4878876cb184118de8227382cfb16d31dc and run gopherjs build --tags=levelupjs on it.

But it is much stranger than that: basically the error vanishes and the package compiles perfectly as soon as I edit qualifiedName to include a log.Print() statement, which I did to start debugging. After a go get the error stopped happening and the logged things were being logged to the terminal, as expected. I then removed the log.Print() line and ran go get again. Still no errors.

An hour later the error appeared again in the meantime I had run gopherjs build multiple times in my package, without a problem, and didn't edit or ran anything else. Again, the error vanished after I did the log.Print() trick. This comeback keep happening every once in a while.

See more in the discussion starting at https://gophers.slack.com/archives/C039C0R2T/p1491492286272286.