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package main
import (
"fmt"
)
func main() {
al := make([]string, 0)
al = append(al, "123", "456")
for _, a := range al {
go func() {
fmt.Println(a)
}()
go func(a string) {
fmt.Println(a)
}(a)
}
}
What did you expect to see?
in line 13: warning, loop variable a captured by func literal.
What did you see instead?
2023-05-06.10.18.06.mov
The text was updated successfully, but these errors were encountered:
gopherbot
added
Tools
This label describes issues relating to any tools in the x/tools repository.
gopls
Issues related to the Go language server, gopls.
labels
May 6, 2023
This is working as intended. The loopclosure analyzer only catches references in go statements that are the last statement in a loop body. Otherwise, the goroutine could be synchronized by a number of means, causing the analyzer to produce false positives.
Knowing whether or not the loop value escapes the loop iteration is a surprisingly tricky problem.
Note that there is discussion about changing loop variable semantics in #56010.
This specific example can be caught by an alternative definition of "last statements". Here is an example WiP that IIRC can detect this specific example: https://go-review.git.corp.google.com/c/tools/+/455195 . The 'lastness' is modified 'statement must be able to reach the end of the loop'. These definitions are unfortunately a bit hard to predict. It still does not take much to stop such analyzers. Any expression that may panic or function call stops going backwards.
func foo() {
...
for _, a := range al {
go func() {
fmt.Println(a)
}()
extraCall() // extra function call that can panic or potentially synchronize
go func(a string) {
fmt.Println(a)
}(a)
}
}
Neither syntactic definition ends up entirely satisfying.
Efforts in this direction may end up somewhat moot due to #56010.
gopls version
golang.org/x/tools/gopls v0.11.0
golang.org/x/tools/gopls@v0.11.0 h1:/nvKHdTtePQmrv9XN3gIUN9MOdUrKzO/dcqgbG6x8EY=
github.com/BurntSushi/toml@v1.2.1 h1:9F2/+DoOYIOksmaJFPw1tGFy1eDnIJXg+UHjuD8lTak=
github.com/google/go-cmp@v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
github.com/sergi/go-diff@v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
golang.org/x/exp@v0.0.0-20221031165847-c99f073a8326 h1:QfTh0HpN6hlw6D3vu8DAwC8pBIwikq0AI1evdm+FksE=
golang.org/x/exp/typeparams@v0.0.0-20221031165847-c99f073a8326 h1:fl8k2zg28yA23264d82M4dp+YlJ3ngDcpuB1bewkQi4=
golang.org/x/mod@v0.7.0 h1:LapD9S96VoQRhi/GrNTqeBJFrUjs5UHCAtTlgwA5oZA=
golang.org/x/sync@v0.1.0 h1:wsuoTGHzEhffawBOhz5CYhcrV4IdKZbEyZjBMuTp12o=
golang.org/x/sys@v0.2.0 h1:ljd4t30dBnAvMZaQCevtY0xLLD0A+bRZXbgLMLU1F/A=
golang.org/x/text@v0.4.0 h1:BrVqGRd7+k1DiOgtnFvAkoQEWQvBc25ouMJM6429SFg=
golang.org/x/tools@v0.3.1-0.20221213193459-ca17b2c27ca8 h1:7/HkGkN/2ktghBCSRRgp31wAww4syfsW52tj7yirjWk=
golang.org/x/vuln@v0.0.0-20221109205719-3af8368ee4fe h1:qptQiQwEpETwDiz85LKtChqif9xhVkAm8Nhxs0xnTww=
honnef.co/go/tools@v0.3.3 h1:oDx7VAwstgpYpb3wv0oxiZlxY+foCpRAwY7Vk6XpAgA=
mvdan.cc/gofumpt@v0.4.0 h1:JVf4NN1mIpHogBj7ABpgOyZc65/UUOkKQFkoURsz4MM=
mvdan.cc/xurls/v2@v2.4.0 h1:tzxjVAj+wSBmDcF6zBB7/myTy3gX9xvi8Tyr28AuQgc=
go: go1.19
go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/toad/Library/Caches/go-build"
GOENV="/Users/toad/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/toad/go/go1.19/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/toad/go/go1.19"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/opt/homebrew/Cellar/go/1.19/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.19/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/toad/work/gopls-demo/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/f
olders/g1/tgmnlrdn3vxgv08kdgh9vpkw0000gn/T/go-build537849748=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
What did you expect to see?
in line 13: warning, loop variable a captured by func literal.
What did you see instead?
2023-05-06.10.18.06.mov
The text was updated successfully, but these errors were encountered: