With go1.18rc1 getting error: constraints: package constraints is not in GOROOT

[xmlking]

go get github.com/tidwall/btree@generics
go: downloading github.com/tidwall/btree v1.1.1-0.20220103194347-7411d3930522
github.com/tidwall/btree imports
constraints: package constraints is not in GOROOT (/Users//sdk/go1.18rc1/src/constraints)

[tidwall]

Try changing go get to go1.18rc1 get.

[sjansen]

I'm seeing the problem using go1.18rc1 installed two different ways.

Installer:

$ /usr/local/go/bin/go version
go version go1.18rc1 darwin/arm64
$ /usr/local/go/bin/go get github.com/tidwall/btree@generics
github.com/tidwall/btree imports
	constraints: package constraints is not in GOROOT (/usr/local/go/src/constraints)

go install golang.org/dl/go1.18rc1@latest

$ ~/go/bin/go1.18rc1 version
go version go1.18rc1 darwin/arm64
$ ~/go/bin/go1.18rc1 get github.com/tidwall/btree@generics
github.com/tidwall/btree imports
	constraints: package constraints is not in GOROOT (/Users/sjansen/sdk/go1.18rc1/src/constraints)

Based on the draft release notes, it looks like constraints is being treated as experimental and as such was moved to golang.org/x/exp/constraints

[sjansen]

Unfortunately, adding replace constraints => golang.org/x/exp v0.0.0-20220218215828-6cf2b201936e to my go.mod did not help.

Looks like it's deliberately unsupported: golang/go#35283

[tidwall]

Right now I'm using go1.18beta2.

Once installed run the following commands to produce a Go 1.18 program that uses gitHub.com/tidwall/btree with generics support.

# create a new directory
mkdir helloworld
cd helloworld

# write a Go program "main.go" 
cat > main.go << EOF
package main

import "github.com/tidwall/btree"

func main() {
	var m btree.Map[string, string]
	m.Set("hello", "world")
	println(m.Get("hello"))
}
EOF

# add the Go module dependencies
go1.18beta2 mod init helloworld
go1.18beta2 get github.com/tidwall/btree@generics
go1.18beta2 mod tidy

# run the file program
go1.18beta2 run main.go

output:

hello true

[tidwall]

The "constraints" package is built into 1.18.

[xmlking]

The problem is with go1.18rc1 not with go1.18beta2.

[tidwall]

My bad, my brain was registering beta1 instead of rc1.

I pushed a fix moments ago. Thanks.

[tidwall]

golang/go#50792

[xmlking]

works now.
tested at https://github.com/xmlking/go-workspace

[tidwall]

Now that Go 1.18 is officially released 🎉 I'm gonna close this issue. Thanks!