go/analysis/passes/modernize: add slicesbackward analyzer by abhay1999 · Pull Request #627 · golang/tools

abhay1999 · 2026-04-01T08:21:43Z

Adds a new slicesbackward pass to the modernize suite that suggests
replacing manually-written backward loops over slices with
slices.Backward (Go 1.23).

Before:

for i := len(s) - 1; i >= 0; i-- {
    use(s[i])
}

After:

for _, v := range slices.Backward(s) {
    use(v)
}

The analyzer matches for loops with the exact pattern:

init: i := len(s) - 1 (where s is a slice expression)
cond: i >= 0
post: i--

When every use of i in the body is s[i], those are replaced with a
fresh value variable and the range clause becomes "_, v :=".

When i is used for other purposes too, both index and value are kept:
"i, v := range slices.Backward(s)".

Loops where i is assigned or address-taken inside the body are skipped
to avoid changing program behavior. Loops using = (not :=) in the init
where i is address-taken before the loop are also skipped.

The analyzer is unexported; it is accessible via goplsexport until the
proposal is approved and the API is published.

Fixes golang/go#78484

google-cla · 2026-04-01T08:21:55Z

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gopherbot · 2026-04-01T08:43:17Z

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gopherbot · 2026-04-01T09:04:21Z

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gopherbot · 2026-04-01T09:04:22Z

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gopherbot · 2026-04-01T14:12:48Z

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Patch Set 1:

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gopherbot · 2026-04-01T15:14:05Z

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gopherbot · 2026-04-01T16:34:04Z

Message from Abhay Chaurasiya:

Patch Set 2:

(18 comments)

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Add a new modernize pass, slicesbackward, that suggests replacing manually-written backward loops over slices: for i := len(s) - 1; i >= 0; i-- { use(s[i]) } with the more readable Go 1.23 slices.Backward iterator: for _, v := range slices.Backward(s) { use(v) } The analyzer matches loops with the exact pattern: - init: i := len(s) - 1 (where s is a slice) - cond: i >= 0 - post: i-- If every use of i in the body is of the form s[i], those are replaced with a value variable and the range clause becomes "_, v :=". If i is also used for other purposes, both index and value are kept: "i, v :=". Loops where i is assigned or address-taken inside the body are skipped. Loops using = (not :=) in the init where i is address-taken before the loop are also skipped. The analyzer is unexported; it is accessible via goplsexport until the proposal is approved and the API is published. Fixes golang/go#78484 Signed-off-by: abhay1999 <abhaychaurasiya19@gmail.com>

gopherbot · 2026-04-01T17:03:23Z

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Patch Set 2:

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gopherbot · 2026-04-01T17:03:24Z

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Patch Set 3:

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gopherbot · 2026-04-01T17:03:25Z

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Patch Set 3:

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gopherbot · 2026-04-01T17:03:34Z

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gopherbot · 2026-04-01T17:24:38Z

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Patch Set 4:

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gopherbot · 2026-04-01T17:33:54Z

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Patch Set 4: Auto-Submit+1 Code-Review+2 Commit-Queue+1

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gopherbot · 2026-04-01T17:33:54Z

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gopherbot · 2026-04-01T18:12:10Z

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gopherbot · 2026-04-01T18:12:11Z

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gopherbot · 2026-04-02T06:13:55Z

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Patch Set 4:

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Adds a new slicesbackward pass to the modernize suite that suggests replacing manually-written backward loops over slices with slices.Backward (Go 1.23). Before: for i := len(s) - 1; i >= 0; i-- { use(s[i]) } After: for _, v := range slices.Backward(s) { use(v) } The analyzer matches for loops with the exact pattern: - init: i := len(s) - 1 (where s is a slice expression) - cond: i >= 0 - post: i-- When every use of i in the body is s[i], those are replaced with a fresh value variable and the range clause becomes "_, v :=". When i is used for other purposes too, both index and value are kept: "i, v := range slices.Backward(s)". Loops where i is assigned or address-taken inside the body are skipped to avoid changing program behavior. Loops using = (not :=) in the init where i is address-taken before the loop are also skipped. The analyzer is unexported; it is accessible via goplsexport until the proposal is approved and the API is published. Fixes golang/go#78484 Change-Id: Ic920cc149c4a3ff2524f4d17f347ec48ab43d05a GitHub-Last-Rev: 4b3470a GitHub-Pull-Request: #627 Reviewed-on: https://go-review.googlesource.com/c/tools/+/761740 Reviewed-by: Alan Donovan <adonovan@google.com> Auto-Submit: Alan Donovan <adonovan@google.com> Reviewed-by: Junyang Shao <shaojunyang@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopherbot · 2026-04-03T20:35:06Z

This PR is being closed because golang.org/cl/761740 has been merged.

abhay1999 force-pushed the add-slicesbackward-modernizer branch from a291394 to 324ca70 Compare April 1, 2026 15:12

abhay1999 force-pushed the add-slicesbackward-modernizer branch from 324ca70 to f0618d3 Compare April 1, 2026 16:35

abhay1999 force-pushed the add-slicesbackward-modernizer branch from f0618d3 to 4b3470a Compare April 1, 2026 16:57

gopherbot closed this Apr 3, 2026

abhay1999 deleted the add-slicesbackward-modernizer branch April 4, 2026 01:48

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