Format sources into the error message when loading codegen backends

[nagisa]

cc rust-lang/rustc_codegen_cranelift#1447
cc @bjorn3

[rustbot]

r? @cjgillot

(rustbot has picked a reviewer for you, use r? to override)

[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[bjorn3]

Thanks!

[nagisa]

Full disclosure: As an alternative approach I have also explored impl<E> From<E> for DiagnosticMessage and similar. While that's way more reusable in the end, I felt like there are too many design questions that come up as a result of doing so for a PR as this:

• How do we format the stuff printed?
• How do we allow adding additional context to the errors we want to output like this? Do we allow pulling in something like anyhow? Do we impl<E> From<(&str, E>)> DiagnosticMessage? Add additional methods to the context?
• etc.

I think it may still be wortwhile to add an ability to print plain std::error::Errors nicely to the diagnostic infrastructure, but that’s better off as its own change.

[cjgillot]

r? @bjorn3

[bjorn3]

@bors r+

[bors]

📌 Commit 1dc3ab0 has been approved by bjorn3

It is now in the queue for this repository.