time: TestLocalZoneAbbr fails when run from Brazil

[jucie]

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

go version devel +835dfef Wed Jul 26 13:29:59 2017 +0000 windows/amd64

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

set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\jucie\go
set GORACE=
set GOROOT=C:\Go
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\jucie\AppData\Local\Temp\go-build507317643=/tmp/go-build -gno-record-gcc-switches
set CXX=g++
set CGO_ENABLED=1
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config

What did you do?

Tried to compile and test go toolset.
git pull
cd src
all

What did you expect to see?

A clean compile and test output.

What did you see instead?

--- FAIL: TestLocalZoneAbbr (0.00s)
zoneinfo_windows_test.go:19: Parse failed: parsing time "Wed, 26 Jul 2017 19:01:29 -03" as "Mon, 02 Jan 2006 15:04:05 MST": cannot parse "-03" as "MST"

Obs.: I compiled and tested in Brazil. Brasilia timezone is GMT -03.

session.txt

[ALTree]

Here's a reproducer that does not require the machine to be in Brasil

package main

import (
	"fmt"
	"time"
)

func main() {
	br, _ := time.LoadLocation("America/Sao_Paulo")
	t1 := time.Now()
	t1 = time.Date(t1.Year(), t1.Month(), t1.Day(),
		t1.Hour(), t1.Minute(), t1.Second(), 0, br)
	_, err := time.Parse(time.RFC1123, t1.Format(time.RFC1123))
	if err != nil {
		fmt.Println(err)
	}
}

$ go run prova.go
parsing time "Tue, 01 Aug 2017 17:35:45 -03" as "Mon, 02 Jan 2006 15:04:05 MST": cannot parse "-03" as "MST"

The issue is in the time.Parse(time.RFC1123, t1.Format(time.RFC1123)) line.

The test assumes that Parse, when called with layout time.RFC1123, will always be able to parse a value generated by Format(time.RFC1123), but this is wrong because even though RFC1123 uses the zone abbreviation (like MST), Format will fallback to the numeric abbreviation (like -07) if the current timezone has no abbreviation, but Parse is stricter and it won't accept -07 in the layout says MST when parsing back the time value.

IANA has been phasing out invented timezone abbreviations, and in the above snippet Format prints "America/Sao_Paulo" as -03, which is rejected by Parse when Parse is given a layout with the abbreviation MST.

A possible fix is to change the test to use time.RFC1123Z, which is like time.RFC1123 except the timezone is always in numeric form (like -03), which is guaranteed to work (unlike invented abbreviations, which as I said IANA is phasing out in newer tzdata releases).

[gopherbot]

Change https://golang.org/cl/52430 mentions this issue: time: use RFC1123Z in test to force numeric zone abbreviation

[ALTree]

@jucie Any chance you could try out the patch at https://golang.org/cl/52430 and confirm it fixes the issue on your machine?

[ALTree]

@jucie Or not, do not try it out. As pointed out it made the test too weak to be actually useful. I'll send a different patch.