Also shouldn't the answer to 5) be: Depends on what exactly the licenses of the used libraries are, but usually lol no?
The situation is exactly that: a GPL library incorporated into an MIT project:
"You wrote a library in Rust and uploaded it to Cargo using the GPL license. Someone grabs it via cargo and uses it in their own project, which is distributed with the MIT license."
A GPL-non-compatible example would be a Business Source License or something non-free. It’s impossible for you to merge a BSL project and a GPL project, because the GPL would require that the result be usable for any purpose, and the BSL would require that the result is not used in production.
https://www.gnu.org/licenses/gpl-faq.html#WhatDoesCompatMean
The same answer in the FAQ (https://www.gnu.org/licenses/gpl-faq.html#WhatDoesCompatMean) contains a caveat mentioned by Tomte's sibling comment (https://news.ycombinator.com/item?id=39840391): the distribution as a whole must be GPL-licensed.
Suppose that you wrote an MIT-licensed Hello World function (one work) and have a copy of someone else's GPL-licensed FizzBuzz function (a separate work). If you distribute both works together (in the same repository, for example) then the combination (a new work) must be under the same GPL version (or a later version, if the license notice for the FizzBuzz function that function says something like "or any later version" [1].
If you write and then distribute a Fibonacci function which calls someone else's GPL'd add function (or your Fibonacci function body includes code from that GPL'd add function), then your distributed Fibonacci function must be under the same GPL version (or a later one, if the license grant lets you).
That‘s not happening in Drew‘s second scenario.
See Tomte's sibling comment to yours (https://news.ycombinator.com/item?id=39840391) and my own other comment (https://news.ycombinator.com/item?id=39841923).
