When you run "go vet" explicitely against go1.4.go, it ignores
the "+build !go1.5" tag and, of course, throws a syntax error:
$ go vet go1.4.go
can't load package: package main:
go1.4.go:5:1: expected 'package', found 'STRING' "You need Go 1.5 or higher to compile gocryptfs!"
Unfortunatey, this is how https://goreportcard.com/ seems to call
"go vet", and means we get 0% on the "go vet" test and see this
error:
An error occurred while running this test (strconv.Atoi: parsing " go1.4.go": invalid syntax)
By reworking the logic to use a non-existant package we get an
uglier error
$ GOROOT=/opt/go1.4.3 /opt/go1.4.3/bin/go build
go1.4.go:7:8: cannot find package "You_need_Go_1.5_or_higher_to_compile_gocryptfs" in any of:
/opt/go1.4.3/src/You_need_Go_1.5_or_higher_to_compile_gocryptfs (from $GOROOT)
/home/jakob/go/src/You_need_Go_1.5_or_higher_to_compile_gocryptfs (from $GOPATH)
profiling.go:6:2: cannot find package "runtime/trace" in any of:
/opt/go1.4.3/src/runtime/trace (from $GOROOT)
/home/jakob/go/src/runtime/trace (from $GOPATH)
but make "go vet" happy.
As noticed by @riking, the logic in the bash script will break
when Go 1 version numbers reach double-digits.
Instead, use a build tag "!go1.5" to cause a syntax error:
$ /opt/go1.4.3/bin/go build
can't load package: package github.com/rfjakob/gocryptfs:
go1.4.go:5:1: expected 'package', found 'STRING' "You need Go 1.5 or higher to compile gocryptfs!"
Fixes https://github.com/rfjakob/gocryptfs/issues/133
