[tools] go/analysis/passes/modernize: fix slicesbackward unused value

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Gopher Robot (Gerrit)

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Apr 29, 2026, 5:25:22 PM (19 hours ago) Apr 29

to Madeline Kalil, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, golang...@luci-project-accounts.iam.gserviceaccount.com, Alan Donovan, golang-co...@googlegroups.com

Gopher Robot submitted the change with unreviewed changes

Unreviewed changes

5 is the latest approved patch-set.
The change was submitted with unreviewed changes in the following files:

```
The name of the file: go/analysis/passes/modernize/slicesbackward.go
Insertions: 6, Deletions: 4.

@@ -203,15 +203,17 @@
 				})
 			}
 
-			// Replace the loop header with a range over slices.Backward.
+			// Replace the loop header with a range over slices.Backward. In
+			// well-typed code, at least one of the index or value variables must be
+			// referenced inside the loop body (otherUses + sliceIndexes > 0).
 			var vars string
-			if otherUses == 0 && len(sliceIndexes) > 0 {
+			if otherUses == 0 { // sliceIndexes > 0
 				// All uses of i are s[i]; drop the index variable.
 				vars = fmt.Sprintf("_, %s", elemName)
-			} else if otherUses > 0 && len(sliceIndexes) == 0 {
+			} else if len(sliceIndexes) == 0 { // otherUses > 0
 				// Index i is not used in any s[i] expressions; drop the value variable.
 				vars = indexIdent.Name
-			} else {
+			} else { // otherUses > 0 && sliceIndexes > 0, keep both variables.
 				vars = fmt.Sprintf("%s, %s", indexIdent.Name, elemName)
 			}
 			header := fmt.Sprintf("%s := range %sBackward(%s)", vars, prefix, sliceStr)
```

Change information

Commit message:

go/analysis/passes/modernize: fix slicesbackward unused value

The slicesbackward modernizer should omit the declaration of v
if only the slice index i is used within the loop.

Adapted from Jah-yee's work in CL 770700 and CL 768700

For golang/go#78629

Change-Id: I53aec72f2645fffda655e6108ded87bbf42e4c7e

Reviewed-on: https://go-review.googlesource.com/c/tools/+/771760

Reviewed-by: Alan Donovan <adon...@google.com>

Auto-Submit: Madeline Kalil <mka...@google.com>

LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>

Files: