Incorrect behaviour of time.Date function

[sharmaayush358]

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

$ go version
go1.15.7 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GO111MODULE="off"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOENV="/home/user/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/user/go-code/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/user/go-code"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/user/.cache/bazel/_bazel_user/b97476d719d716accead0f2d5b93104f/external/go_sdk"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/user/.cache/bazel/_bazel_user/b97476d719d716accead0f2d5b93104f/external/go_sdk/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build854370504=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://play.golang.org/p/hyyLG_o8ERS

What did you expect to see?

The two time instances should be equal.

What did you see instead?

The two time instances are not equal.

This is happening because (t *Time) setLoc has this if statement

if loc == &utcLoc {
    loc = nil
}

Instead of checking for the equality of pointers, we should check for the equality of the Location structs that they point to.
So, I propose changing it to

if *loc == utcLoc {
    loc = nil
}

[mvdan]

Have you seen this piece of the docs?

Note that the Go == operator compares not just the time instant but also the Location and the monotonic clock reading. Therefore, Time values should not be used as map or database keys without first guaranteeing that the identical Location has been set for all values, which can be achieved through use of the UTC or Local method, and that the monotonic clock reading has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u) to t == u, since t.Equal uses the most accurate comparison available and correctly handles the case when only one of its arguments has a monotonic clock reading.

Your program works fine with Time.Equal.

[sharmaayush358]

While that is fine, I still believe the way setLoc is implemented should be changed. The location provided to time.Date in the playground example was infact utcLoc but the setLoc function deemed it not to be utcLoc because of the way it is implemented.

[mvdan]

A location is a pointer, though. If you make a copy of the UTC location, it is not guaranteed to be treated the same. I'm not really sure why you're doing the copy.

If you must do the copy for some reason, and you want equality to be more lax, then you want the Equal method.

[seankhliao]

See previously #45961 for considering time.Time