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cmd/cgo: C.* cannot be used for type constraints #52542

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hajimehoshi opened this issue Apr 25, 2022 · 4 comments
Closed

cmd/cgo: C.* cannot be used for type constraints #52542

hajimehoshi opened this issue Apr 25, 2022 · 4 comments
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@mdempsky
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compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Backlog

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@hajimehoshi
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What version of Go are you using (go version)?

$ go version
go version go1.18 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/hajimehoshi/Library/Caches/go-build"
GOENV="/Users/hajimehoshi/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/hajimehoshi/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/hajimehoshi/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/hajimehoshi/test/generics/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 x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/60/khbk2xqn1c5bml1byjn89dwc0000gn/T/go-build3847202091=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Try compiling:

package main

import "C"

func Foo[T ~C.int](x T) T {
        return x
}

func main() {
}

What did you expect to see?

The compilation succeeds

What did you see instead?

The compilation failed

$ go build main.go
# command-line-arguments
./main.go:5:13: undefined: C
@ianlancetaylor ianlancetaylor changed the title cmd/compile: C.* cannot be used for type constraints cmd/cgo: C.* cannot be used for type constraints Apr 25, 2022
@ianlancetaylor ianlancetaylor added the NeedsFix The path to resolution is known, but the work has not been done. label Apr 25, 2022
@ianlancetaylor ianlancetaylor added this to the Go1.19 milestone Apr 25, 2022
@ianlancetaylor
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Rolling forward to 1.20. Please comment if you disagree. Thanks.

@ianlancetaylor ianlancetaylor modified the milestones: Go1.19, Go1.20 Jun 24, 2022
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
@mknyszek mknyszek modified the milestones: Go1.20, Backlog Nov 30, 2022
@mknyszek
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In triage, we think this should at least have a nice error message.

@gopherbot
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Change https://go.dev/cl/453977 mentions this issue: cmd/cgo: walk {FuncType,TypeSpec}.TypeParams fields

@mdempsky
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This will be fixed in 1.20. Note though that ~C.int isn't a valid type parameter constraint, because C.int isn't its own underlying type.

@golang golang locked and limited conversation to collaborators Nov 30, 2023
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@mdempsky mdempsky

Labels
compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
Projects
Release Status & Release Blockers
Status: Done
Milestone
Backlog
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5 participants
@hajimehoshi @mdempsky @mknyszek @ianlancetaylor @gopherbot