As discussed in #3146 current master does not work with this extension.

To quote @pfitzseb out of context:

we could potentially run against nightly with Pkg support

Currently the fallback environment is built with +stable while it might be more beneficial to build it with +nightly once that lands in JuliaLang/juliaup#384

The other part of the problem is that on 1.9 there are packages that were removed from the standard library but not yet vendored. So in such cases the fallback environment would still fail, unless it could support Pkg that are not vendored.

To approach the problem from the other side: it could be useful to add an extra option to set the executable path for the language server separately from the normal Julia path, so the language server could be set to run with a stable Julia release, and code can be ran with nightly Julia.

After much silly problems, this workaround seems to do the trick:

#!/usr/bin/env bash
set -e
if [ -z "$JULIA_LANGUAGESERVER" ]; then
	exec julia +dev "$@"
else
	exec julia +release "$@"
fi