Golang x/tools/gopls: modernize bloop: Can't use b.Loop() if loop contains b.StopTimer/b.StartTimer

Go version

go version go1.24.1 linux/amd64

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=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/jille/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/jille/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2881335881=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/jille/src/ilsa-sanity/go.mod'
GOMODCACHE='/home/jille/go/pkg/mod'
GONOPROXY=''
GONOSUMDB='src.hexon.nl/*'
GOOS='linux'
GOPATH='/home/jille/go'
GOPRIVATE=''
GOROOT='/usr/lib/go-1.24'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/jille/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go-1.24/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I ran modernize which upgraded some benchmarking loops from for i := 0; i < b.N; i++ {} to for b.Loop {} on https://github.com/bluele/psort/blob/master/psort_test.go.

What did you see happen?

The benchmark times out after 10 minutes, whereas it previously finished in seconds.

What did you expect to see?

The code changed by modernize should do the exact same thing.

I suspect we need to teach modernize not to touch loops which call b.StopTimer() :(

Comment From: gabyhelp

Related Issues

• x/tools/gopls/internal/analysis/modernize: replacing non-equivalent code #73073 (closed)
• testing: b.StopTimer breaks b.Loop #72922 (closed)
• x/tools/gopls: modernizer max changes logic #71878 (closed)
• x/tools/gopls/internal/analysis/modernize: rangeint: transformation unsound when loop variable is defined outside loop #73009 (closed)
• x/tools/gopls: modernize's rangeint check is too aggressive #74295 (closed)

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