x/tools/gopls/internal/analysis/modernize: rangeint suggests changes that alter some programs' semantics #75289
Description
Go version
go version go1.25.1 darwin/amd64
Output of go env in your module/workspace:
N/AWhat did you do?
I ran modernize (commit 0b1eed0) on the following program (playground), which outputs 10:
package main
import "fmt"
func main() {
var i int
defer func() { fmt.Println(i) }()
for i = 0; i < 10; i++ {
// deliberately empty
}
}What did you see happen?
REDACTED.go:8:6: for loop can be modernized using range over int
Fix suggested:
Replace for loop with range 10
i.e.
func main() {
var i int
defer func() { fmt.Println(i) }()
- for i = 0; i < 10; i++ {
+ for i = range 10 {
// deliberately empty
}
}What did you expect to see?
No suggested change, or at least not that one. The semantics of the resulting program are indeed different from the original program's: whereas the original program prints 10, the resulting program (playground) prints 9:
package main
import "fmt"
func main() {
var i int
defer func() { fmt.Println(i) }()
for i = range 10 {
// deliberately empty
}
}