Also, not having a license file isn't a messy situation, that means “this project is protected under Berne Convention copyright“: the author is the only one holding every rights on the code and every use that is not explicitly allowed is a copyright infringement (unless it's fair use).
That being said, it would be nice from the author to put the code under a permissive license to allow other people to play with his code too (at the moment, even forking it is a copyright infringement…).
Not that it changes much, but from the GitHub Terms of Service:
> By setting your repositories to be viewed publicly, you agree to allow others to view and "fork" your repositories https://help.github.com/en/articles/github-terms-of-service#...
First: GitHub has a Terms of Service which was somewhat-recently amended to make this license grant explicit:
https://help.github.com/en/articles/github-terms-of-service#...
"Any User-Generated Content you post publicly, including issues, comments, and contributions to other Users' repositories, may be viewed by others. By setting your repositories to be viewed publicly, you agree to allow others to view and 'fork' your repositories (this means that others may make their own copies of Content from your repositories in repositories they control)."
(Crucially, it doesn't require an open-source license, though.)
Second: even without that, there's such a thing as an implied license:
https://en.wikipedia.org/wiki/Implied_license
Like, if you write something down on a piece of paper, you can't then sue the owner of the paper for copyright infringement.
Similarly, if you upload code to GitHub, and tell it to share your code, you can't then sue them for sharing your code, ToS or no ToS.
And that license grant is solely through github as a service, it's unclear that a local clone is even permitted.
That license grant has been added specifically to make GitHub itself waterproof (AIUI), so it makes sense it doesn't extend to user's rights. Look, but don't touch.
The ToS doesn't say there's an implicit reproduction license, though; it says there's an explicit reproduction license.
The other licenses can still be argued to be implicit. For instance, you have a decent argument that local clones are an implicit license – GitHub provides a "Clone or download" button directly on the repo page, and it's one of the main use cases of GitHub. (Other arguments exist.)
Then it's totally excluded from my claim which aims «every use that is not explicitly allowed». :)
Your first point doesn't really bring much though, since it falls in the “explicitly allowed” part of my comment.
Overall, my whole point stands still: if anyone went on GitHub, downloaded the project and did anything with it that went beyond fair use, that would be a copyright infringement because neither the author nor GitHub granted you any permission to do so.
[1] https://en.wikisource.org/wiki/Convention_for_the_Protection...
But, can you compile it ? I'm not sure… Better ask your lawyer. And what about running the compiled binary ? I don't think you're allowed to do that.
Hosting that code yourself somewhere else would be illegal though.
It wasn't offered for free local reproduction since that right was not explicitly granted, and Github's license grant does not grant it either (as far as my reading goes). Though the country you're in may have a private copy exception, in which case you'd be in the clear I think (depending on the specifics of that exception).
And in turn, the project you submitted it to cannot re-licence that patched section of code (e.g. become either GPL licenced) without your permission, as it does not belong to them.
(Edit for clarity)
[0] https://help.github.com/en/articles/github-terms-of-service#...
Edit: I edited my comment to say “could” instead of “would” because the original author could argue that the author of the patch implicitly gave him the right to redistribute his patch by contributing it to a public repository. I'm not sure it would stand in court, but I'd say it would have a non-null chance of success.
But If the author, who initially claimed the project was a learning project, decided to use it commercially, he clearly wouldn't be allowed to use the patch. (and again, it could be different if the patch author willingly contributed to a commercial product).
The answer is that making the change is already usually copyright infringement (though I think some countries have a concept of private copies being exempt from these types of restrictions). But redistribution of your patch would definitely be copyright infringement because a license to create a derived work was not given to you -- and patches are by definition derived works.