cmd/go: go toolchain version switch doesn't work when only language version is set in go.mod

[hyangah]

Go version

go 1.21.4

Output of go env in your module/workspace:

$ GOTOOLCHAIN=auto go env
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available

What did you do?

Had a project created with a go built from tip during 1.22 dev cycle.
The go.mod file has language version, but not toolchain version yet.

$ cat go.mod
module example.com/bug

go 1.22

What did you see happen?

Since go1.22.0 is released, I expected the go command to pick up go1.22.0 when version switching is needed.
Instead, most go commands failed in the module since there is no toolchain named go1.22.

What did you expect to see?

~/bug$ go version
go version go1.21.4 darwin/amd64
~/bug$ GOTOOLCHAIN=auto go env
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go version
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go mod tidy
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go mod tidy -go=1.21.4
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go get go@latest
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go get toolchain@latest
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go build
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available
~/bug$ GOTOOLCHAIN=auto go build ./...
go: downloading go1.22 (darwin/amd64)
go: download go1.22 for darwin/amd64: toolchain not available

[fzipp]

According to #62278 (comment) it has to be either

go 1.22.0

or

go 1.22
toolchain 1.22.0

[seankhliao]

i think this is working as expected, 1.22 refers to the in development version, not a language version

[seankhliao]

Duplicate of #62278

[hyangah]

@fzipp go 1.22 is a valid syntax.
@seankhliao Thanks for the pointer to the issue. The spec allows a language version and when the toolchain is available to handle the language version, we need to do better (given all the confusion and noise in #62278).