Disable compilation on some extensionless files

[natepisarski]

This commit prevents the compiler from overwriting certain extensionless source files with a binary.

As it stands, if you have /home/joe/file1:

 fn main(){}

and compile it

rustc /home/joe/file1

It will replace the source (file1) with a binary called file1, destroying the source without warning or error.

This commit completely disallows compiling without a file extension, but still allows compiling with an inccorect (i.e not .rs) extension.

[rust-highfive]

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

[alexcrichton]

Thanks @natepisarski! The tracking issue for this is #13019, so you could actually put Closes #13019 in one of the commits as well if you'd like to close the issue when this is merged.

I think there may also be some more cases that need to be handled here (can you add tests for all these as well?)

• Compiling an extensionless file into a library should be ok as suffixes/prefixes are added
• rustc foo -o bar should be ok
• rustc foo -o foo should probably be ok because it was explicitly requested

When adding tests, could you add them to the src/test/run-pass test suite? Thanks again!

[natepisarski]

@alexcrichton I can do all of these. Probably not in the most timely manor, but I can get them done.

[alexcrichton]

Ok, thanks @natepisarski!

[alexcrichton]

Closing due to inactivity, but feel free to reopen with comments addressed!