Unless Microsoft releases at least one of its products (ms-sql, visual studio, windows, office) under an open source license i'm calling bullshit.
However they are not one of the big 4 as you have listed.
I have heard MS employees talk about open sourcing some of their bigger products and the conversation always comes down to the issue of the third party code (libraries, etc) they use that cannot be open sourced along with the main product.
I'm not defending Microsoft in any way just giving an explanation I have heard over the last few years. I believe Mark Russinovich has talked about open sourcing things a number of times if you want to look into it further.
Why does an extension need to be open source for a program to be called open source?
If someone writes a closed source plugin for LibreOffice or GIMP, does that mean they aren't open source?
They do have gitlab ce that has just a subset of the functionalities from Gitlab Enterprise that is open sourced.
the first line even say: in doubt use gitlab ee
the point here is that core has two distinct meaning in the op question in gitlab pr..
Gitlab ee is their core product, core here meaning their main product..
the fact that the core of that product, here meaning the base the product is built upon, was released as open source does not make the whole product open source..
So, gitlab core\main product is not open source.. But the core\base of that product is..
Microsoft tries to aggressively buy its way into existing mature projects.