Prevent rustc overwriting input files

[varkor]

If rustc is invoked on a file that would be overwritten by the
compilation, the compilation now fails, to avoid accidental loss. This
resolves #13019. Kudos to @estebank, whose patch I finished off.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @eddyb (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[eddyb]

r? @alexcrichton

[alexcrichton]

Thanks for the PR! Would it be possible to perhaps avoid duplicating the invocation of build_output_filenames and reuse it being created elsewhere? Other than that though looks great!

[varkor]

Which invocation of build_output_filenames would be most appropriate to reuse? The one in driver.rs seems to be the only one that is guaranteed to be called — but then the input filename would probably need to be passed to compile_input as well. Is it preferable to add an extra parameter here to avoid the extra invocation?

[eddyb]

@varkor Yes, feel free to change rustc_driver APIs.

[varkor]

Done, thanks!

[alexcrichton]

Thanks! Looks like there's a test that's failing though?

[varkor]

Ah, let an invocation slip through the net. Fixed.

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 3a29f28 has been approved by alexcrichton

[frewsxcv]

@bors rollup