x/tools/gopls/internal/analysis/modernize: replacing non-equivalent code

[chipaca]

gopls version

Build info
----------
golang.org/x/tools/gopls v0.18.1
    golang.org/x/tools/gopls@v0.18.1 h1:2xJBNzdImS5u/kV/ZzqDLSvlBSeZX+pWY9uKVP7Pask=
    github.com/BurntSushi/toml@v1.4.1-0.20240526193622-a339e1f7089c h1:pxW6RcqyfI9/kWtOwnv/G+AzdKuy2ZrqINhenH4HyNs=
    github.com/google/go-cmp@v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
    golang.org/x/exp/typeparams@v0.0.0-20241210194714-1829a127f884 h1:1xaZTydL5Gsg78QharTwKfA9FY9CZ1VQj6D/AZEvHR0=
    golang.org/x/mod@v0.23.0 h1:Zb7khfcRGKk+kqfxFaP5tZqCnDZMjC5VtUBs87Hr6QM=
    golang.org/x/sync@v0.11.0 h1:GGz8+XQP4FvTTrjZPzNKTMFtSXH80RAzG+5ghFPgK9w=
    golang.org/x/telemetry@v0.0.0-20241220003058-cc96b6e0d3d9 h1:L2k9GUV2TpQKVRGMjN94qfUMgUwOFimSQ6gipyJIjKw=
    golang.org/x/text@v0.22.0 h1:bofq7m3/HAFvbF51jz3Q9wLg3jkvSPuiZu/pD1XwgtM=
    golang.org/x/tools@v0.30.1-0.20250221230316-5055f70f240c h1:Ja/5gV5a9Vvho3p2NC/T2TtxhHjrWS/2DvCKMvA0a+Y=
    golang.org/x/vuln@v1.1.3 h1:NPGnvPOTgnjBc9HTaUx+nj+EaUYxl5SJOWqaDYGaFYw=
    honnef.co/go/tools@v0.5.1 h1:4bH5o3b5ZULQ4UrBmP+63W9r7qIkqJClEA9ko5YKx+I=
    mvdan.cc/gofumpt@v0.7.0 h1:bg91ttqXmi9y2xawvkuMXyvAA/1ZGJqYAEGjXuP0JXU=
    mvdan.cc/xurls/v2@v2.5.0 h1:lyBNOm8Wo71UknhUs4QTFUNNMyxy2JEIaKKo0RWOh+8=
go: go1.24.1

but also

/home/john/.cache/go-build/54/542d18e8cf4015d5d32a5913f137addc33e0c03fb15b8e2990b3b4f334431680-d/modernize version devel comments-go-here buildID=542d18e8cf4015d5d32a5913f137addc33e0c03fb15b8e2990b3b4f334431680

go env

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/john/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/john/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2429323114=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/john/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/john/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/john/sdk/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/john/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/john/sdk/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix ./...

What did you see happen?

for loops like

for i = 0; i<N; i++ { ... }

getting changed to

for i = range N { ... }

when i is used after the loop; in the first case it will be N and in the second case it will be N-1 (ignoring other control flow).

What did you expect to see?

I expected the code to not behave differently after running modernize.

Editor and settings

editor was not involved in this

Logs

gopls wasn't involved (but I couldn't figure out a better template for this issue)

[gabyhelp]

Related Issues

• x/tools/gopls/internal/analysis/modernize: rangeint generates correct but not idiomatic transformation #71725 (closed)
• x/tools/gopls/internal/analysis/modernize: rangeint: transformation unsound when loop variable is defined outside loop #73009 (closed)
• x/tools/gopls: loopclosure analysis runs on Go 1.22.0 #65910 (closed)
• x/tools/gopls/internal/analysis/modernize: rangeint should be silent when RHS of 'i < limit' depends on loop var #72726 (closed)
• x/tools/gopls: No warning "loop variable xx captured by func literal". #60016 (closed)
• x/tools/gopls: modernize misses modernization of 3-way "max" #72733
• x/tools/gopls: #52425 (closed)
• x/tools/gopls/internal/analysis/modernize: range over int rule doesn't consider potential slice appends #73022 (closed)
• x/tools/gopls: yet more modernizer bugs #71847 (closed)
• x/tools/gopls: modernize x/exp/maps.Clear for Go >= 1.21 #70717 (closed)

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