Add nightly-only support for Cargo unremap trim-paths files in rust-gdb

[Urgau]

This PR adds support in rust-gdb for the un-remapping file produced by Cargo with -Ztrim-paths (rust-lang/cargo#17303). This support is nightly-only, and only activated when RUST_GDB_TRIM_PATHS=unstable is set.

An example of the unremap file:

{"v":1}
{"rust_version":"1.96.0-nightly","workspace_root":"/home/me/app"}
{"from":"/cargo/build-dir","to":"/home/me/app/target"}
{"from":"/cargo/registry/6f17d22d3f0a95d1","to":"/home/me/.cargo/registry/src/index.crates.io-6f17d22d3f0a95d1"}
{"from":"/rustc/abc123","to":"/home/me/.rustup/toolchains/nightly/lib/rustlib/src/rust"}

Disclaimer: I used Gemini to figure out how to interact with GDB, GDB doc is not very discoverable, everything can be sourced to the docs (links in the source code).

cc @weihanglo

[rustbot]

r? @Mark-Simulacrum

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[weihanglo]

How should we test this? Do you have any manual steps to follow?

View changes since the review

[weihanglo]

Side note: I am adding tests in rust-lang/rust exercising the unremap file itself.

[Urgau]

I tested it by manually modifying the rust-gdb script to point to my local gdb_trim_paths.py ("$GDB_PYTHON_MODULE_DIRECTORY/gdb_trim_paths.py" to "$YOUR_RUST_LOCAL_CHECKOUT/src/etc/gdb_trim_paths.py"), as otherwise you need to do x.py dist which annoying.

Then I created a dummy hello-world Cargo project, cargo build-it and manually added the hello-world.trim-paths.jsonl file (since the Cargo bump PR is not yet merged).

After that you can just execute rust-gdb as always:

1. rust-gdb target/debug/hello-world & run
2. or rust-gdb & file target/debug/hello-world & run

Tip: show substitute-path shows all the substitutions.

[weihanglo]

Should we print a warning for unrecognized version?

View changes since the review

[Urgau]

I don't know, I added one at first, but I don't want users to have one (or more) warnings about unsupported versions, which can happen when Cargo update the version, in particular since this logic is been handled automatically.

There isn't a way to suppress the warning at the moment.