`.\x fmt std` panics

[ChrisDenton]

Doing x test std will run the std's tests.

Doing x fmt std results in:

thread 'main' panicked at 'entry failed with std: The system cannot find the file specified. (os error 2)', format.rs:257:25
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Doing x fmt library/std works but I expected fmt to work similarly to test.

[jyn514]

Fixing this for std isn't hard, but fixing it in a general way is somewhat tricky because we don't have Steps to look at for format. I think we should only support shortcuts for directories, and only three directories deep to avoid making the search too expensive (I picked three so that tools in src/tools will be supported).

Relevant code:

rust/src/bootstrap/format.rs

Line 198 in d094016

walker.add(path);

[jieyouxu]

I would like to give this a try
@rustbot claim