[weihanglo]

Stabilization report

What is stabilized

With trim-paths object scope and debuginfo on, Cargo writes <artifact>.trim-paths.json¹ beside each final artifact. This "unremap" file, maps the remapped paths back to local ones.

This stabilizes debugger script changes: rust-gdb and rust-lldb by default load {gdb,lldb}_trim_paths.py, which read the unremap files and apply them through GDB substitute-path or LLDB target.source-map to set up source file path substitutions.

Note that we already apply an unremap for /rustc/$RUSTC_COMMIT_HASH paths, so it wouldn't be a new capability per se, just an extension of it.

What changes

• After stabilization, set RUST_{GDB,LLDB}_TRIM_PATHS=0 to opt out.
  Before, it required RUST_{GDB,LLDB}_TRIM_PATHS=unstable to enable.
• After stabilization, both scripts are shipped on all channels.
  Before, they were shipped only on nightly.

Why we don't want to stabilize

• This makes debugger scripts relying on Cargo-specific file format, inversing the dependency relation.
• There is no integration test for them.
  (and debugger scripts actually don't have many tests)

Docs

See Cargo's the "Unremap files" section:
https://github.com/rust-lang/cargo/blob/ac74ae3c603b9efce95b07383b46d3103e834d9a/doc/book/src/reference/profiles.md?plain=1#L337-L386

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Should be shipped after #163881 (or along with that)

Footnotes

1. Example of the format at: https://github.com/rust-lang/cargo/blob/ac74ae3c603b9efce95b07383b46d3103e834d9a/doc/book/src/reference/profiles.md?plain=1#L367-L381 ↩

[Urgau]

Cargo stabilized profile.trim-paths and the unremap file at rust-lang/cargo#17488.

@rfcbot merge compiler

[rust-rfcbot]

@Urgau has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Mark-Simulacrum
• @TaKO8Ki
• @davidtwco
• @estebank
• @jdonszelmann
• @jieyouxu
• @nnethercote
• @oli-obk
• @petrochenkov
• @spastorino
• @wesleywiser

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[jieyouxu]

cc @Walnut356 (since you may be interested as well)

[nnethercote]

Why we don't want to stabilize

• This makes debugger scripts relying on Cargo-specific file format, inversing the dependency relation.

Can someone explain more about this dependency relation?

[weihanglo]

The change creates a compatibility guarantee for toolchain's debugger support for a format defined by Cargo. rust-gdb and rust-lldb after this look for the <artifact>.trim-paths.json file and load their mappings by dfeault, unless expliclitly disabled.

"Inverting the dependency relation" may be a too strong word, though. Just now debugger and build tool is coupled to some extent, though for the majority it has net benefit.

[wesleywiser]

It looks like if the file doesn't exist or is not in the format we expect, we'll print a warning message but the debugging experience (loading of visualizers, etc) is otherwise not degraded by the failure. Is that correct?

[weihanglo]

It looks like if the file doesn't exist

This is a silent skip, as trim-paths is off by default for now in Cargo. Changing the default is tracked in rust-lang/cargo#17586.

or is not in the format we expect, we'll print a warning message but the debugging experience (loading of visualizers, etc) is otherwise not degraded by the failure. Is that correct?

Yes. Correct.