time: TZ=UTC does not cause Location field to be nil

[pzinovkin]

What did you do?

package main

import (
	"fmt"
	"os"
	"time"
)

func main() {
	fmt.Println("TZ:", os.Getenv("TZ"))
	fmt.Printf("%#v\n", time.Now())
	fmt.Printf("%#v\n", time.Now().UTC())
}

bash-3.2$ TZ="UTC" go run tt.go
TZ: UTC
time.Time{sec:63623205117, nsec:63974400, loc:(*time.Location)(0x110e4e0)}
time.Time{sec:63623205117, nsec:64010002, loc:(*time.Location)(nil)}

What did you expect to see?

Both strings to contain nil Location.

System details

go version go1.8 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/pzinovkin"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.8/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.8/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/fv/0mdc02116kn485ml31tvs26w0000gn/T/go-build085816660=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
GOROOT/bin/go version: go version go1.8 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.8 X:framepointer
uname -v: Darwin Kernel Version 16.4.0: Thu Dec 22 22:53:21 PST 2016; root:xnu-3789.41.3~3/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.12.3
BuildVersion:	16D32
lldb --version: lldb-360.1.70

[peterGo]

src/time/zoneinfo.go:

// NOTE(rsc): Eventually we will need to accept the POSIX TZ environment
// syntax too, but I don't feel like implementing it today.

[pzinovkin]

Isn't it already supported?
https://github.com/golang/go/blob/master/src/time/zoneinfo_unix.go#L56

Anyway it should fallback to UTC. And UTC must contain nil loc like in second string.

[ianlancetaylor]

Your program clearly shows that the time package does respect the TZ environment variable.

I think the question is: should the time package require that TZ=UTC cause a local Time value to have a nil Location field? The docs do say that "All UTC times are represented with loc==nil, never loc==&utcLoc." The question is whether that applies when the local time zone is UTC.

[pzinovkin]

Your program clearly shows that the time package does respect the TZ environment variable.

I'm not sure about that.

bash-3.2$ go version
go version go1.7.5 darwin/amd64
bash-3.2$ cat tt.go
package main

import (
	"fmt"
	"os"
	"time"
)

func main() {
	fmt.Println("TZ:", os.Getenv("TZ"))
	fmt.Printf("%#v\n", time.Now().Location())
}
bash-3.2$ TZ="MSK" go run tt.go
TZ: MSK
&time.Location{name:"", zone:[]time.zone(nil), tx:[]time.zoneTrans(nil), cacheStart:0, cacheEnd:0, cacheZone:(*time.zone)(nil)}
bash-3.2$ TZ="UTC" go run tt.go
TZ: UTC
&time.Location{name:"", zone:[]time.zone(nil), tx:[]time.zoneTrans(nil), cacheStart:0, cacheEnd:0, cacheZone:(*time.zone)(nil)}

[ianlancetaylor]

@pzinovkin That is not the right test. Try actually fetching some field from the location first. For example, try adding

fmt.Println(time.Now().Location())

(which will call the String method) before you print out the contents of the location.

[pzinovkin]

You're right. Thanks.

bash-3.2$ cat tt.go
package main

import (
	"fmt"
	"os"
	"time"
)

func main() {
	fmt.Println("TZ:", os.Getenv("TZ"))
	fmt.Println(time.Now())
	fmt.Println(time.Now().Location())
}
bash-3.2$ TZ="ROK" go run tt.go
TZ: ROK
2017-02-21 04:16:47.677760884 +0900 KST
ROK
bash-3.2$ TZ="" go run tt.go
TZ:
2017-02-20 19:16:51.373521089 +0000 UTC
UTC
bash-3.2$ TZ="Asia/Irkutsk" go run tt.go
TZ: Asia/Irkutsk
2017-02-21 03:17:54.094113655 +0800 +08
Asia/Irkutsk

[pzinovkin]

@bradfitz is this issue already resolved?

[bradfitz]

Sorry, I quickly interpreted the "You're right" as the issue no longer existing.

On second read, it looks like we're still trying to determine whether Location should always be nil, like @ianlancetaylor says in #19202 (comment):

The question is whether that applies when the local time zone is UTC.

[admtnnr]

This looks like #19486?

[ianlancetaylor]

Yes, I think Russ addresses this issue in #19486 when he said "Go always maintains a distinction between local and UTC times, even when TZ=UTC in the environment."

I'm going to close this again. If you think this is wrong, please follow up with some code that shows a problem that is not related to internal details of the time package.