Go vet misses closure using variable from outer loop #32876
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Duplicate of #16520 |
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Nov 21, 2022
…statements like if, switch, and for In golang/go#16520, there was a suggestion to extend the current loopclosure check to check more statements. The current loopclosure flags patterns like: for k, v := range seq { go/defer func() { ... k, v ... }() } For this CL, the motivating example from golang/go#16520 is: var wg sync.WaitGroup for i := 0; i < 10; i++ { for j := 0; j < 1; j++ { wg.Add(1) go func() { fmt.Printf("%d ", i) wg.Done() }() } } wg.Wait() The current loopclosure check does not flag this because of the inner for loop, and the checker looks only at the last statement in the outer loop body. The suggestion is we redefine "last" recursively. For example, if the last statement is an if, then we examine the last statements in both of its branches. Or if the last statement is a nested loop, then we examine the last statement of that loop's body, and so on. A few years ago, Alan Donovan sent a sketch in CL 184537. This CL attempts to complete Alan's sketch, as well as integrates with the ensuing changes from golang/go#55972 to check errgroup.Group.Go, which with this CL can now be recursively "last". Updates golang/go#16520 Updates golang/go#55972 Fixes golang/go#30649 Fixes golang/go#32876 Change-Id: If66c6707025c20f32a2a781f6d11c4901f15742a GitHub-Last-Rev: 04980e0 GitHub-Pull-Request: #415 Reviewed-on: https://go-review.googlesource.com/c/tools/+/452155 Reviewed-by: Tim King <taking@google.com> Run-TryBot: Tim King <taking@google.com> Reviewed-by: Alan Donovan <adonovan@google.com> gopls-CI: kokoro <noreply+kokoro@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Run-TryBot: Alan Donovan <adonovan@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
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What version of Go are you using (
go version)?Does this issue reproduce with the latest release?
What operating system and processor architecture are you using (
go env)?go envOutputWhat did you do?
Normally
go vetreturn an error if you have a loop with a goroutine function call with closure:./prog.go:17:23: loop variable i captured by func literalhttps://play.golang.org/p/PAg99GZMa7__8
But if you have nested loops with a closure that captures a variable from the outerloop and you have a goroutine inside an inner loop
go vetwill not return an error.https://play.golang.org/p/zDsGfz0iESI
What did you expect to see?
go vetreturned an error:loop variable i captured by func literalhttps://play.golang.org/p/PAg99GZMa7__8
What did you see instead?
same results but no
go veterrorhttps://play.golang.org/p/zDsGfz0iESI
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