On NixOS, with homemanager or with a project-specific version of VSCode, the feature “Check for Extensions Update” always indicates “All extension are up to date.” even when this is not the case.
What exactly do you mean by “project specific”? For me VScode just updates all the plugins automatically.
Are you perhaps talking about a declaratively managed VScode? In that case (by my understanding) the “source” of an extension is left empty or set tp “locally installed” or whatever it is called exactly. So VScode will never consider it out dated, as it does not have a source to ask for a newer version available.
It’s … a little more complex than that. There was a time, for a few months earlier this year, when my declaratively-managed VScode did tell me about outdated extensions. I paid attention to the output.
Some were ones I had added directly (via pkgs.vscode-utils.extensionsFromVscodeMarketplace) and I had to update them.
Some were ones from nixpkgs, and I sent a PR to update those.
Then it stopped doing that, just as mysteriously again.
And now there’s nothing that makes me remember to run the script and manually check which are out of date (because that script just shows the current version, regardless of whether it’s the same as what’s installed).
I’m not sure how intentional either change was, nor what is the right behaviour for the general user case, but it was handy to know.