--remap-path-prefix no longer works for compiler messages

[nicholasbishop]

Code

Create a directory and put a Rust file with bad syntax in it:

mkdir src
echo bad > src/test.rs

Then compile it with:

rustc --remap-path-prefix=src=MODIFIED src/test.rs

I expected to see output like this:

error: expected one of `!` or `::`, found `<eof>`
 --> MODIFIED/test.rs:1:1
[snip]

Instead, the path is not modified and I get:

error: expected one of `!` or `::`, found `<eof>`
 --> src/test.rs:1:1
[snip]

Version it worked on

rustc 1.53.0 (53cb7b0 2021-06-17)

Version with regression

rustc 1.54.0 (a178d03 2021-07-26)

[nicholasbishop]

Bisected:

searched nightlies: from nightly-2021-03-17 to nightly-2021-08-03
regressed nightly: nightly-2021-05-13
searched commits: from 5c02926 to 21e92b9
regressed commit: e1ff91f

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2021-03-17 --preserve --script=./bisect-check.py 

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-low

[inquisitivecrystal]

After further discussion, there appears to be a consensus in the Prioritization Working Group that this should be P-medium for the moment. Sorry for the noise!

[dtolnay]

FYI @cbeuw @michaelwoerister, since this bisects to #83813. Would one of you be able to take a look?