Please answer these questions before submitting your issue. Thanks!

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

Atleast go 1.7 & 1.8 have this error

What operating system and processor architecture are you using (go env)?

Can reproduce this error on Mac & Linux

What did you do?

I can build my program fine even if there is a file that is only supposed to compile with go 1.9 with a build constraint for example:

https://github.com/golang/net/blob/master/context/go19.go

The ParseDir function in "go/parser" does not respect the "+build 1.9" constraint in the comment and tries to parse the file anyways causing it to throw an error.

What did you expect to see?

I expected the ParseDir to ignore the file as the file has an Build Constraint which should signal ParseDir which is trying to parse all *.go" files for their AST that it cannot fully parse this file.

What did you see instead?

The ParseDir throws a mysterious error:

src/golang.org/x/net/context pkg cause error: src/golang.org/x/net/context/go19.go:15:14: expected type, found '=' (and 1 more errors)