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SA4006: detect unused writes with += #1329

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cespare opened this issue Oct 18, 2022 · 0 comments · May be fixed by #1555
Open

SA4006: detect unused writes with += #1329

cespare opened this issue Oct 18, 2022 · 0 comments · May be fixed by #1555
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false-negative

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@cespare
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cespare commented Oct 18, 2022 •
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$ staticcheck -debug.version
staticcheck 2022.1.3 (v0.3.3)

Compiled with Go version: go1.18.4
Main module:
        honnef.co/go/[email protected] (sum: h1:oDx7VAwstgpYpb3wv0oxiZlxY+foCpRAwY7Vk6XpAgA=)
Dependencies:
        github.com/BurntSushi/[email protected] (sum: h1:GaI7EiDXDRfa8VshkTj7Fym7ha+y8/XxIgD2okUIjLw=)
        golang.org/x/exp/[email protected] (sum: h1:qyrTQ++p1afMkO4DPEeLGq/3oTsdlvdH4vqZUBWzUKM=)
        golang.org/x/[email protected] (sum: h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=)
        golang.org/x/[email protected] (sum: h1:id054HUawV2/6IGm2IV8KZQjqtwAOo2CYlOToYqa0d0=)
        golang.org/x/[email protected] (sum: h1:OKYpQQVE3DKSc3r3zHVzq46vq5YH7x8xpR3/k9ixmUg=)

Go version is 1.19.2 linux/amd64.

Example program:

package main

func main() {
	dir := "a"
	dir += "/b"
}

Staticcheck doesn't complain about that. But if I tweak it to

package main

func main() {
	dir := "a"
	dir = dir + "/b"
}

Then I get

x/x.go:5:2: this value of dir is never used (SA4006)

Could SA4006 better detect this case with +=?
@cespare cespare added false-negative needs-triage Newly filed issue that needs triage labels Oct 18, 2022
@dominikh dominikh removed the needs-triage Newly filed issue that needs triage label Oct 26, 2022
arp242 added a commit to arp242/go-tools that referenced this issue May 31, 2024
@arp242
SA4006: Fix for compound operators, increment/decrement
a6b8923 
In the case of compound operators such as +=, -=, etc we need to use the
left-hand side to get the value.

For IncDec we need a different codepath from AssignStmt altogether.

Fixes dominikh#1329
@arp242 arp242 linked a pull request May 31, 2024 that will close this issue
Open
arp242 added a commit to arp242/go-tools that referenced this issue Jun 1, 2024
@arp242
SA4006: Fix for compound operators, increment/decrement
577de29 
In the case of compound operators such as +=, -=, etc we need to use the
left-hand side to get the value.

For IncDec we need a different codepath from AssignStmt altogether.

Fixes dominikh#1329
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SA4006: Fix for compound operators, increment/decrement arp242/go-tools
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@dominikh @cespare