cmd/compile: line number lost for error message

[griesemer]

https://play.golang.org/p/Qc-jCD5inV produces

main.go:3: //go:nowritebarrier only allowed in runtime

but the latest repo ( go version devel +bf45099 Tue Dec 27 16:53:33 2016 -0800 darwin/amd64 ) has lost the information:

<unknown line number>: //go:nowritebarrier only allowed in runtime

This is a regression from 1.7.

[odeke-em]

@griesemer I encountered this and fixed it in my CL https://go-review.googlesource.com/c/34562 by changing the signature of pragmaValue to return an error as well and then finally doing

p.error(syntax.Error{Pos: pos, Line: line, Msg: err.Error()})

[griesemer]

@odeke-em Thanks for this. I have a fix that's much smaller that we might consider for 1.8. Your fix may be cleaner, but at this point we want to have minimal changes, if any.

[odeke-em]

Awesome, sounds like a plan.

[gopherbot]

CL https://golang.org/cl/34721 mentions this issue.