It works for me.

In your go env output, I see GOEXPERIMENT=''. Are you sure you set GOEXPERIMENT in your environment?

I just did:

export GOEXPERIMENT=rangefunc
nvim main.go

I'm using coc.nvim, but wouldn't expect neovim native LSP to behave differently.

When I try to set it as environment variables, I get

go: unknown GOEXPERIMENT rangefunc

I had previously tried to use the environment variable to add the configuration of gopls and got the same error, but I thought that was an issue with how I was setting up the configuration.

I have tried it again, but I run into the same error:

            lspconfig.gopls.setup({
                capabilities = addCmpCapabilities(lspconfig.gopls.capabilities),
                settings = {
                    gopls = {
                        allowModfileModifications = false,
                        gofumpt = true,
                        codelenses = {
                            generate = true,
                            tidy = true,
                            upgrade_dependency = true,
                            vendor = true,
                        },
                        buildFlags = { "-tags", "goexperiment.rangefunc" },
                        directoryFilters = { "-**/node_modules", "-**/.git" },
                        env = {
                            GOEXPERIMENT = "rangefunc",
                        },
                    },
                },
            })

go: unknown GOEXPERIMENT rangefunc

Hmm, do you have multiple versions of go installed? Is it possible that the go your neovim sees is not go 1.22?

So I updated my go binary (not just the toolchain) to go1.22 and got rid of the error:

go: unknown GOEXPERIMENT rangefunc

However, the InvalidRangeExpr error is still reported despite adding GOEXPERIMENT=rangefunc to everywhere I could:

• go env with go env -w GOEXPERIMENT=rangefunc
• The local project env with .envrc
• The gopls configuration as outlined above.

Could you share gopls logs from a short session that demonstrates the problem? That would help us investigate why it isn't working in your session.
https://github.com/golang/tools/blob/master/gopls/doc/troubleshooting.md#capture-logs

My bad. I was using Mason on Neovim, which installs its own gopls which is at v14.2, when I force it to use my installed gopls v15.0-pre.3, I was able to get it to work, but only with a local env variable

• Setting go env with go env -w GOEXPERIMENT=rangefunc did not work
• Setting the go pls configurations (both env and buildFlags also did not work.

@stephenafamo hi, did you solve this problem?

@RunThem The solution is to update gopls in Mason:

:MasonInstall gopls