In this case both Pylance and Pyright are developed by Microsoft.
I suspect that open-sourcing in anything at all is essentially a long-term PR/marketing/recruiting investment, as well as as positioning Microsoft as the keepers and main developers of what has become an important standard.
That said, by "reuse" I mean that end-users are free to install the non-free binaries extracted from VS code, which interoperate with any text editor that implement a language client. They are all on NPM.
I suspect that open-sourcing in anything at all is essentially a long-term PR/marketing/recruiting investment, as well as as positioning Microsoft as the keepers and main developers of what has become an important standard.
That said, by "reuse" I mean that end-users are free to install the non-free binaries extracted from VS code, which interoperate with any text editor that implement a language client. They are all on NPM.