Golang testing: iterators break t.Helper()

Go version

go version go1.24.1 darwin/amd64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/willi/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/willi/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/m7/j4gfn87j6tbbjqkjkllgjvg40000gn/T/go-build3215631796=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/willi/<redacted>/go.mod'
GOMODCACHE='/Users/willi/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/willi/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/Cellar/go/1.24.1/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/willi/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/Cellar/go/1.24.1/libexec/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK='/Users/willi/<redacted>/go.work'
PKG_CONFIG='pkg-config'

What did you do?

package repro

import (
    "strings"
    "testing"
)

func TestHelper(t *testing.T) {
    helper(t)
}

func helper(t *testing.T) {
    t.Helper()
    // t.Fatal("this correctly displays repro_test.go:9 as its origin")
    for range strings.SplitSeq("a,b,c", ",") {
        t.Fatal("this incorrectly shows repro_test.go:16 (this line) as its origin, ignoring t.Helper()")
    }
}

What did you see happen?

repro_test.go:16: this incorrectly shows repro_test.go:16 (this line) as its origin, ignoring t.Helper()

What did you expect to see?

repro_test.go:9: this incorrectly shows repro_test.go:16 (this line) as its origin, ignoring t.Helper()

Comment From: mrwonko

Note that if I add a t.Helper() inside of the loop body, the error message points to iter.go:61 instead (but the path is wrong due to a separate issue)

Comment From: gopherbot

Change https://go.dev/cl/656775 mentions this issue: testing: recognize helper functions that use range-over-function