"replacements"

[Eh2406]

"replacements" (in cargo the patch section and the replace) are a way to substitute the code for one package with some other code. In dart it is called dependency-overrides

This issue is to split off and continue the conversation from pubgrub-rs/pubgrub#39.

[Eh2406]

To summarize the comments from pubgrub-rs/pubgrub#39 so far:

mpizenberg: pubgrub-rs/pubgrub#39 (comment)

Patch

It seems that a patch replaces directly the list of existing versions of a package by one explicitely provided in the patch. I tend to believe this is then just a matter of doing exactly that a DependencyProvider implementation.

Replace

Are the versions specified authorized to be new (non-existing in crates)? If not, this is just a matter of adjusting the get_dependencies method of a DependencyProvider implementation. If yes, it also needs to adjust the list_available_versions.

[Eh2406]

I think the bugs in Cargo's resolver have to do with the fact that a selected version can report its package name, but with "replacements" that may not be the same as the name the dependency asked for. In pubgrub, thanks to @mpizenberg's foresight to use generics, we know that we never rely on V.get_package() == P for anything, as we did not ask for a get_package method.
As such I think you are wright, it is just technical complexity in the implementation of a DependencyProvider