File inclusion with an explicit destination path

[LukeMathWalker]

As discussed in #9, this PR changes the behaviour of the include attribute:

• #[assay(include = ["folder/my_file.rs"]) will copy the file into the root folder of the test working directory (i.e. file.rs);
• #[assay(include = [("folder/my_file.rs", "folder/my_renamed_file.rs"]) will instead use the specified destination path.

I have a few questions on the implementation that I've left as TODO comment in the code. I'd appreciate your input there.

Closes #9

[LukeMathWalker]

An alternative here would be to add a generic parameter S: AsRef<Path> and tie both inputs to use S.
We cannot have destination_path: Option<impl AsRef<Path>> because it causes an inference error when the path is omitted.

[mgattozzi]

@LukeMathWalker would it be possible to do this so they can be separate types or is the inference breaking here?

pub fn include(&self, source_path: S, destination_path: Option<D>)
where S: AsRef<Path>,
      D: AsRef<Path>

[LukeMathWalker]

That still failed, but I managed to work around the inference issue by forcing D to be PathBuf in the code generated by the proc macro for the None case.

[mgattozzi]

This is great! 🤩 I think we can pass off on parsing errors for now as I don't have a great idea of what I want there, but overall these changes are fantastic! Let's take out the TODO around the panic and if the double generic works let's do that!

[LukeMathWalker]

Thanks for the review!
TODOs are gone, the generic issue has been solved and the panics have been polished. It should be ready for a second look 😁