> The source code has been released by Microsoft under the open-source MIT license, but the product available for download (Visual Studio Code) is licensed under this proprietary license.
I used to consider releasing software under the MIT license to be more generous since there are no conditions other than attribution. However by now I can see that releasing under a copyleft is actually more generous than a permissive license since the copyleft conditions also binds the author of the software to continue releasing their code under an open-source license. Turns out Richard Stallman was right after all.
The author of software (or generally the copyright holder) is not bound by the terms of their own license, so they can publish the same software and/or later versions under different licenses however they see fit.
This applies equally if their own license is MIT or if it's GPL/copyleft.
(From that point of view, Microsoft would be able to release VSCode as GPL while also shipping binaries under a proprietary license, if they wanted to.)
Things get more complicated when they aren't really the authors because they have merged contributions from other authors, e.g. pull requests. Then what happens depends on the license used by the other authors for their contributions. Sometimes the contribution's license is implied, or legally unclear. To avoid problems, some diligent organisations require contributors to sign or confirm something to make it clearer, before they accept contributions to be merged.
In understand that, but if people license their work under an MIT license then there is nothing impeding whoever manages the repository to slap a new license on the code even if people already contributed to it.
> To avoid problems, some diligent organisations require contributors to sign or confirm something to make it clearer, before they accept contributions to be merged.
That's a very generous way of saying they're having people sign away their rights under a copy-left license.
I used to consider releasing software under the MIT license to be more generous since there are no conditions other than attribution. However by now I can see that releasing under a copyleft is actually more generous than a permissive license since the copyleft conditions also binds the author of the software to continue releasing their code under an open-source license. Turns out Richard Stallman was right after all.