time: AddDate() should use UTC if loc is nil

[KilledKenny]

I added all my env info at the end since everything is reproducible on play.golang.org

What did you do?

I called time's AddDate whit a time object that was missing a location

https://play.golang.org/p/S-ZZKabdyL

package main

import (
    "time"
)

func main() {
    time.Time{}.AddDate(0,0,0)
}

What did you expect to see?

I expected that AddDate would follow the behavior specified by loc documentation that it should use the default UTC as location when calling Date

Only the zero Time has a nil Location.
In that case it is interpreted to mean UTC.

Ref: https://golang.org/src/time/time.go?s=2261:2352

The expected behavior can be seen here: https://play.golang.org/p/-9Bp0rjphc

What did you see instead?

panic: time: missing Location in call to Date

goroutine 1 [running]:
panic(0xd6660, 0x1030a078)
    /usr/local/go/src/runtime/panic.go:481 +0x700
time.Date(0x1, 0x1, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
    /usr/local/go/src/time/time.go:1030 +0xa0
time.Time.AddDate(0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
    /usr/local/go/src/time/time.go:658 +0x100
main.main()
    /tmp/sandbox596209771/main.go:8 +0x60

My suggested solution

$ git diff
diff --git a/src/time/time.go b/src/time/time.go
index d9dbd34..6ead1ce 100644
--- a/src/time/time.go
+++ b/src/time/time.go
@@ -652,7 +652,8 @@ func Since(t Time) Duration {
 func (t Time) AddDate(years int, months int, days int) Time {
        year, month, day := t.Date()
        hour, min, sec := t.Clock()
-       return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec), t.loc)
+       location := t.Location()
+       return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec), location)
 }

 const (

Dose the fix look good? Should I submit it for review?

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

$ go version
go version go1.6.1 linux/amd64

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

$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/simonr/go"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

[quentinmit]

It looks like this panic has been in place since at least 2011; it's a simple change but I think it's probably too late for Go 1.7.

@KilledKenny Can you please submit your patch via Gerrit? (see https://golang.org/doc/contribute.html)

@rsc @bradfitz You seem to own the time package, do you think we should change this and do you agree we should wait for Go 1.8?

[KilledKenny]

@quentinmit Yep, I'm aware of the contribute guidelines, I will attempt to submit the fix during the weekend.

[rsc]

It should probably be fixed, but let's wait for Go 1.8. It's clearly not critical since it has gone this long. Thanks.

[KilledKenny]

@quentinmit I have submitted it now: https://go-review.googlesource.com/23561

[gopherbot]

CL https://golang.org/cl/23561 mentions this issue.