time: LoadLocation(now.Local().Location().String()) != now.Local().Location()

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6.2 windows/amd64
2. What operating system and processor architecture are you using (go env)?
   windows 10 x64

set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=D:\golang
set GORACE=
set GOROOT=c:\go
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GO15VENDOREXPERIMENT=1
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0
set CXX=g++
set CGO_ENABLED=1

1. What did you do?

package main

import (
    "time"
    "fmt"
)

func main() {
    now :=time.Now()

    fmt.Println("now:",now)
    fmt.Println("now.Location:",now.Location())
    fmt.Println("now.Local().Location:",now.Local().Location())

    l,err:=time.LoadLocation(now.Location().String())
    fmt.Println(l,err)
    l,err=time.LoadLocation(now.Local().Location().String())
    fmt.Println(l,err)
}

/*
now: 2016-05-06 09:47:54.1544589 +0800 CST
now.Location:
now.Local().Location:
UTC <nil>
UTC <nil>
*/

1. What did you expect to see?
   Sorry, my English is not good.
   now.Location().String() returns "Asia/ShangHai"
2. What did you see instead?
   In non UTC time zone, time.LoadLocation(now.Local().Location().String()) != now.Local().Location()

now.Location() returns ""
now.Local().Location() returns ""
time.LoadLocation(now.Local().Location().String()) returns "UTC"

Is it bug, or is it just like that? I can't get the local time zone.
now.Location().String() returns ""
now.Local().Location().String() returns ""

l, err := time.LoadLocation("Local")
l.String() returns ""

t2, _ := time.Parse("2006-01-02T15:04:05.999999999Z07:00 MST", time.Now().Format("2006-01-02T15:04:05.999999999Z07:00 MST"))

t2.Location() returns ""
t2.Local().Location() returns ""

I try to use IDEA IntelliJ debugging.

Found in the abbrev function
a.std= "CST";
a.dst= "CST";
return a.std, a.dst.

But stdname, dstname :=abbrev(I) is the result of stdname = "" dstname="CST".

C:\go\src\time\zoneinfo_windows.go

func abbrev(z *syscall.Timezoneinformation) (std, dst string) {
    stdName := syscall.UTF16ToString(z.StandardName[:])
    a, ok := abbrs[stdName]
    if !ok {
        dstName := syscall.UTF16ToString(z.DaylightName[:])
        // Perhaps stdName is not English. Try to convert it.
        englishName, err := toEnglishName(stdName, dstName)
                //[ DEBUG]englishName = "China Standard Time"
        if err == nil {
            a, ok = abbrs[englishName]
            if ok {
                                // [DEBUG] a.std = "CST"  
                                // [DEBUG] a.dst = "CST"  
                return a.std, a.dst
            }
        }
        // fallback to using capital letters
        return extractCAPS(stdName), extractCAPS(dstName)
    }
    return a.std, a.dst
}

C:\go\src\time\zoneinfo_windows.go

func initLocalFromTZI(i *syscall.Timezoneinformation) {
    l := &localLoc

    nzone := 1
    if i.StandardDate.Month > 0 {
        nzone++
    }
    l.zone = make([]zone, nzone)

    stdname, dstname := abbrev(i)
        // DEBUG  stdname =""
        // DEBUG dstname ="CST"

    std := &l.zone[0]
    std.name = stdname

Also, now.Zone() normal.

    name,offset:=t.Zone()
    fmt.Println(name,offset)

// output: CST 28800

[bradfitz]

Sorry, I don't think we guarantee that a time.Location's String() returns a unique key which can be used to load that *Location back again.

For instance, I remember an old bug where something like LoadLocation("EST") could mean United State's east coast or Australia's east coast depending on who ran it. (I forget the details)

Some similar old bugs: #4838 #3790

I don't think there's any code to change here, but maybe we just need to document the expectations better.

[alexbrainman]

I don't think there's any code to change here

What about this:

U:\>type main.go
package main

import (
        "fmt"
        "time"
)

func main() {
        fmt.Println(time.Local)
}

U:\>go run main.go


U:\>

Does it look correct to you?

Alex

[gopherbot]

CL https://golang.org/cl/23078 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31144 mentions this issue.

[rsc]

CL 31144 is unrelated, sorry, I typed the wrong bug number into the commit message.

This bug seems to be fixed by Alex's commit CL 23078. Now that Local.String() returns "Local" not "", everything is OK.