• Significant memory improvements (@heschik). Dependency test variants and vendored packages are no longer considered "workspace packages".
• Smart autocompletion for "append" (@muirdm).
• A "fill struct" code action to suggest populating a struct literal with default values (@luciolas, @joshbaum).
• Better cgo support with Go 1.15 (@heschik). Learn more: golang/go#35721 (comment).
• Code lens to run Go tests directly in the editor (@martskins). Currently opt-in:

"gopls": {
    "codelens": {
        "test": true,
    }
}

• Improved folding in composite literals (@joshbaum).
• Pop-up suggestion to run go mod vendor when inconsistent vendoring detected (@stamblerre).
• Respect GOPRIVATE for all document links and links on hover (@findleyr).
• A full list of issues resolved in this release can be found in the gopls/v0.4.2 milestone.

gopls/dev.go2go: You can use the new go2go prototype with gopls. See golang/go#39619.