Feature request: path prefix remapping

rustfmt can emit diagnostics (eg syntax errors), but has no way to normalize the source filenames.

rustc has a --remap-path-prefix option so that all places where source file names are emitted (diagnostics, debug info, etc) can be normalized by, for example, removing an absolute path of a build directory.

It would be nice if rustfmt also implemented this option so the same kinds of remapping can be performed on its diagnostics.

To Reproduce

$ cat t.rs
fn main() {{}
$ rustfmt t.rs
error: this file contains an unclosed delimiter
 --> /home/jsgf/t.rs:1:15
  |
1 | fn main() {{}
  |           -   ^
  |           |
  |           unclosed delimiter

rustfmt shows the full path - not the path passed to it, and has no option for remapping this.

Expected behavior

rustfmt --remap-path-prefix /home/jsgf/= t.rs would show just t.rs:1:15 as the error path.

Meta

• rustfmt version: rustfmt 1.4.15-stable (530eadf 2020-06-02)
• From where did you install rustfmt?: rustup
• How do you run rustfmt: rustfmt

Start at the rustfmt command-line entry point and trace how diagnostic source filenames are produced for the t.rs reproducer. Determine where a --remap-path-prefix option would be parsed and applied, then verify that the example reports t.rs:1:15 instead of the absolute path.