Marking as Go 1.12 since the behavior is not new.

CC @rsc @bcmills

Additionally, the error you expected to see looks a bit broken to me—looks like a bad format string. cc @mvdan

I think that the formatting error was fixed in the latest master but I'm still using 1.11 Beta 1. I'll revisit this for Beta 2 / RC 1.

I cannot reproduce this on go version devel +d278f09333 Thu Jul 19 05:40:37 2018 +0000 darwin/amd64

...go/src/demo % cat demo.go
//+build hello
package demo

import "testing"

type Demo struct {
	Field string
}

func NewDemo(v string) *Demo {
	return &Demo{
		Field: v,
	}
}

func TestDemo(t *testing.T) {
	v := NewDemo("hello world")
	t.Log(v)
}
...go/src/demo % go test -c -o test.bin
# demo
./demo.go:1: +build comment must appear before package clause and be followed by a blank line
...go/src/demo % ls
demo.go

This still seems to be an issue both on Windows and Linux using:

• go version devel +d278f09333 Thu Jul 19 05:40:37 2018 +0000 windows/amd64
• go version devel +d278f09333 Thu Jul 19 05:40:37 2018 +0000 linux/amd64

See the image below:

@ysmolsky this is probably because the code was in a non _test.go file? In my case it was in such a file.

Right. I am sorry! Here we go:

...go/src/demo % mv demo.go demo_test.go
...go/src/demo % go test -c -o test.bin
...go/src/demo % go test
# demo
./demo_test.go:1: +build comment must appear before package clause and be followed by a blank line
FAIL	demo [build failed]

Reproduced.

Change https://golang.org/cl/125215 mentions this issue: cm/go/internal/test: make vet run when compiling

@iwdgo says this broke race detector on windows: #27089
Could somebody take a look please?

Issue cannot be reproduced when using go 1.11.1

The issue is still present in Go 1.11.1. Place the code exactly as it's written in a _test.go file and the problem should be reproduced.