time: In() does not replace the time zone correctly

[feketegy]

Go version

go version go1.24.0 linux/arm64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN='/go/bin'
GOCACHE='/root/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2315358320=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='arm64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/srv/ca-if-api/go.mod'
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/root/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_arm64'
GOVCS=''
GOVERSION='go1.24.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

The time.In() function documentation states:

In returns a copy of t representing the same time instant, but with the copy's location information set to loc for display purposes.

But it changes the time as well, essentially converting the time to the time zone offset.

Example: https://go.dev/play/p/-s0CkU9VSC7

What did you see happen?

1. In the example below, t1 shows the time in UTC that is used as the base time.
2. Creating a fixed zone with time.FixedZone that offsets it -8 hours from UTC (in seconds).
3. Setting t2 time zone with the time.In() function.
4. t2 should show 2025-04-01 02:15:24 -0800 GMT -8:00 but the time gets offset by -8 hours, showing 2025-03-31 18:15:24 -0800 GMT-8.

Is this the expected behavior?

Example: https://go.dev/play/p/-s0CkU9VSC7

package main

import (
	"fmt"
	"time"
)

func main() {
	t1, _ := time.Parse(time.RFC3339, "2025-04-01T02:15:24Z")
	fmt.Printf("\nOriginal time in UTC: %s", t1)

	fz := time.FixedZone("GMT-8", -8*60*60)

	t2 := t1.In(fz)
	fmt.Printf("\n\nChanged time zone: %s", t2)
}

What did you expect to see?

If t1 in the example is 2025-04-01 02:15:24 UTC, then t2 should also show 2025-04-01 02:15:24 -0800 GMT -8:00, switching the time zone only, but not the date/time.

[gabyhelp]

Related Issues

• time: ParseInLocation does not adjust timezone offset when seconds are not explicitly set #53919 (closed)
• time: The Time object created with time.Date() in the timezone `America/New_York` returns incorrect information when DST is applied. #66554 (closed)
• time: time.Time get wrong local time zone for some days #16553 (closed)
• time: time.LoadLocation returns incorrect time zone #34101 (closed)
• time: `time#Format` using `time.RFC3339` using `time.Time` with `time.Location` `Europe/London` should use `+00:00` instead of `Z` #68164 (closed)
• time: time.now () uses the time zone to modify the problem #65228 (closed)
• time: time ParseInLocation error #66987 (closed)
• time: inconsistent handling timezone offset for a location #35152 (closed)
• time: document Location's effect on Time more? #23316 (closed)
• time: notice system timezone changes #28020

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[JunyangShao]

As @seankhliao mentioned, this is working as intended, thanks for asking the question. 👍

[seankhliao]

Working as intended.
It represents the same absolute instant in time, not the same civil time.

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