time: time.Local is always UTC on Android

[tmm1]

initLocal() in zoneinfo_android.go is hard-coded to UTC:

go/src/time/zoneinfo_android.go

Lines 43 to 46 in bc495c5

	func initLocal() {
	// TODO(elias.naur): getprop persist.sys.timezone
	localLoc = *UTC
	}

func initLocal() {
	// TODO(elias.naur): getprop persist.sys.timezone
	localLoc = *UTC
}

x/mobile currently uses a hack to set time.Local for gomobile android apps (golang/mobile@730f563), but that predates the availability of tzdata on android (80b31c0).

cc @eliasnaur @crawshaw #13581 #10857

[gopherbot]

CL https://golang.org/cl/43754 mentions this issue.

[gwik]

Same issue on iOS, should I create a separate issue ?

[eliasnaur]

Yes, create a separate issue and reference this one.

[tmm1]

Since I wasn't able to write a patch to fix this in golang, I ended up calling this from init() in my app instead:

func fixTimezone() {
	out, err := exec.Command("/system/bin/getprop", "persist.sys.timezone").Output()
	if err != nil {
		return
	}
	z, err := time.LoadLocation(strings.TrimSpace(string(out)))
	if err != nil {
		return
	}
	time.Local = z
}

[tmm1]

I found out there's a C api available for fetching properties, which should make it much simpler to support Android timezones from golang directly (via cgo): __system_property_get in <sys/system_properties.h>

My previous attempt in CL43754 was abandoned because it was too hard to call os/exec from the time package.

[eliasnaur]

Good catch. If you mail a CL before the end of this month, it should be eligible for Go 1.11.

[tmm1]

Good catch. If you mail a CL before the end of this month, it should be eligible for Go 1.11.

I don't plan to submit any CLs, but others should feel free to do so.

You will need to first get a decision one way or another about whether the time package is allowed to depend on cgo, as originally proposed in #20797

[uudashr]

Do we have progress on this?