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fix(trim-paths): /cargo/deps fallback sources - #17338

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fix(trim-paths): /cargo/deps fallback sources #17338
epage merged 2 commits into
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@weihanglo weihanglo commented Aug 8, 2026 •
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What does this PR try to resolve?

This is similar to /rustc/deps the existing pattern in rustc bootstrap.

The /cargo/path is confusing enough, and it also contain vendored dependencies outside workspace root hence so.

How to test and review this PR?

This also updates the docs to leave the remap prefixes unspecified.
Happy to split them if needed.

LLM disclosure: This was found during the experiment of #17309 with LLM against rust-lang/rust

@weihanglo
docs(trim-paths): leave remap prefixes unspecified
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@weihanglo
fix(trim-paths): /cargo/deps fallback sources
4ca8632 
This is similar to `/rustc/deps` the existing pattern in rustc bootstrap
@weihanglo weihanglo added the A-trim-paths Area: path sanitization in resulting binaries label Aug 8, 2026
@rustbot rustbot added A-documenting-cargo-itself Area: Cargo's documentation S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 8, 2026
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epage commented Aug 8, 2026

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Not sure I understand the confusion. Deps seems like a broad term and the naming within it; I thought this was related to registry packages or something.

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weihanglo commented Aug 8, 2026

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Not sure I understand the confusion. Deps seems like a broad term and the naming within it; I thought this was related to registry packages or something.

My idea was that /cargo/path actually now have

  • Path dependencies outside the workspace
  • Vendored dependencies outside the workspace (include git and registyr deps being vendored)
  • Any other non-normal cases like CARGO_HOME symlinks and make it hard to determine the original sources location. (We dont have test covering this, yes, thought not sure if it is worthy)

Not sure if we want to try hard and categorize them all, since they are not on common path. So, I feel like we can have a broader /cargo/deps to consolidate them all.

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epage approved these changes Aug 8, 2026
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I can see that but "deps" still feels werid. Not worth trying to decide if it is good enough since this is unstable.

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epage added this pull request to the merge queue Aug 8, 2026
Merged via the queue into rust-lang:master with commit a07c49a Aug 8, 2026
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@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 8, 2026
@weihanglo weihanglo mentioned this pull request Aug 11, 2026
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weihanglo deleted the trim-paths-path-deps branch August 11, 2026 00:22
@weihanglo weihanglo mentioned this pull request Aug 11, 2026
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rust-bors Bot pushed a commit to rust-lang/rust that referenced this pull request Aug 11, 2026
@bors
Auto merge of #160938 - weihanglo:update-cargo, r=weihanglo
6660e28 
Update cargo submodule

10 commits in b07e5a08651da80108eb65d7dc769ee04589f9bf..eb98b54bc9f3c74519f43d066cb3fd02ebc88df0
2026-08-07 21:51:16 +0000 to 2026-08-11 16:00:29 +0000
- feat(trim-paths): honor workspace prefix override from env (rust-lang/cargo#17349)
- fix(clean): respect target with --doc (rust-lang/cargo#17322)
- chore(renovate): Use a 3day minimum release age (rust-lang/cargo#17346)
- test: Handle non-deterministic compilation order (rust-lang/cargo#17347)
- docs(ref): Add missing config env variables (rust-lang/cargo#17345)
- fix(trim-paths): workspace remap under -Zroot-dir (rust-lang/cargo#17337)
- Fix funding link (rust-lang/cargo#17344)
- fix(trim-paths): `/cargo/deps` fallback sources  (rust-lang/cargo#17338)
- doc: don't use mergeable info and json together (rust-lang/cargo#17336)
- docs: document --output-format for cargo doc (rust-lang/cargo#17325)
@rustbot rustbot added this to the 1.99.0 milestone Aug 12, 2026
@weihanglo weihanglo mentioned this pull request Aug 13, 2026
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@weihanglo weihanglo mentioned this pull request Sep 18, 2026
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github-actions Bot pushed a commit to codeandsolder/cargo-ephemeral that referenced this pull request Oct 6, 2026
@epage
feat(trim-paths): stabilize profile.trim-paths (rust-lang#17488)
784be26 
*[View all
comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/cargo/pull/17488)*

# Stabilization report: `profile.trim-paths`

Resolves rust-lang#12137
Resolves rust-lang/rust#111540
RFC: <https://rust-lang.github.io/rfcs/3127-trim-paths.html>

## What is stabilized

The rustc side `--remap-path-scope` was already stabilized in Rust 1.95
via rust-lang/rust#147611

This stabilizes the Cargo side:

* `profile.<name>.trim-paths = "none" | "object" | "all"`
  in both manifest and config
* The remap rules of how Cargo passes `--remap-path-{prefix,scope}`.
  The exact remap prefixes still stay unspecified.
* The unremap file `<artifact>.trim-paths.json` (schema v1),
  which is emitted beside final artifacts when debuginfo is on.
* `CARGO_TRIM_PATHS_SCOPE` and `CARGO_TRIM_PATHS_REMAP` for build
scripts.

When this is merged and sync in rust-lang/rust,
we'll also stabilize

* The `rust-gdb` and `rust-lldb` unremap loaders.
`RUST_GDB_TRIM_PATHS=unstable` and `RUST_LLDB_TRIM_PATHS=unstable` are
not needed anymore.

See doc for details:

https://github.com/rust-lang/cargo/blob/8814ead110e36ed8fdcf1fdd4009baf82bd78523/doc/book/src/reference/unstable.md?plain=1#L1441-L1645

## What is not stabilized / included

* This doesn't guarantee full sanitization. It is a best-effort feature.
* Other `--remap-path-scope` values in rustc (`macro`, `diagnostics`,
`debuginfo`, `coverage`),
  boolean values, and comma-separated list options.
  These are removed in rust-lang#17432.
  They can come back later when needed.
* A default trim-path value for built-in profiles.
  RFC originall proposed to set `release` to `"object"`.
  This is left for future when this is more adopted and battle-tested.
We have loose stability guarantee for changing profile settings anyway.
* `__CARGO_RUSTC_BOOTSTRAP_WS_REMAP`.
  This stays as an internal thing between rustc bootstrap and cargo
  (see rust-lang#17349, rust-lang#17366)
* Doctest remapping and `documentation` scope.
  This will be integrated in the future incrementally
  when those scopes and features are stable.
* The exact remap prefixes are unspecified as documented.
  However, in practice,
  rustc bootstrap and debugger depend on the stabilized shape,
  so any change needs careful coordination with them.
* Unremap files for artifact deps: deferred, non-blocking.
* `build-rs` API for the two build script variables: deferred,
non-blocking.
* If there are new kinds of artifacts, we can decide whether to remap
freely.

### Doors closed

* The trim-paths profile key name, its shape, and its options.
* The unremap file name suffix `.trim-paths.json` and the v1 schema.
* The environment variable `CARGO_TRIM_PATHS_SCOPE` and
`CARGO_TRIM_PATHS_REMAP`.

## Post-RFC changes

* rustc removed `split-debuginfo` scopes,
  and Cargo followed and stopped caring split debuginfo.
* The RFC remapped the current package to relative paths and every
dependency to `<name>-<version>`.
  In rust-lang#17302 we chose workspace members relative remap,
  so debuggers resolve workspace sources with zero configuration.
The RFC worried that relative paths only work when running from the
right directory,
and symbolication tools need a second process for joining workspace
relative paths.
THe unremap file has `workspace_root`, so the join is fairly mechanical.
  Remap prefixes are unspecified anyway,
  so we can still change if it turns out not ideal.
* The unremap file is new (introduced in rust-lang#17303),
  for helping debugging find sources,
  as well as our keeping remap rules unspecified.
  The RFC had no answer about this.
* `CARGO_TRIM_PATHS_REMAP` build script env is new.
It lets build scripts forward the same rules to C/C++ compilers to flags
like `-fmacro-prefix-map`.
  `cc-rs` has integrated that since rust-lang/cc-rs#1794.

## Feedback

* rustc bootstrap builds the compiler and standard library with
`trim-paths`
  via rust-lang/rust#161049 since 2026-09-02.
This exercises the sysroot remap and the workspace prefix override in
rust-lang/rust CI.
* `cc-rs` forwards the remap rules to C/C++ compiler since 1.3.0:
<https://github.com/rust-lang/cc-rs/releases/tag/cc-v1.3.0>
* Zulip thread: [#t-cargo > stabilization plan for
&rust-lang#96;-Ztrim-paths&rust-lang#96;](https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/stabilization.20plan.20for.20.60-Ztrim-paths.60/with/622955580)
* Call for testing posted on 2026-09-09
*
rust-lang#12137 (comment)
* Included in TWiR issue 669
<https://this-week-in-rust.org/blog/2026/09/16/this-week-in-rust-669/>

## Known limitations

This sanitization is best-effort. See

* rustc:
<https://doc.rust-lang.org/rustc/remap-source-paths.html#caveats-and-limitations>
* Cargo:
<https://github.com/rust-lang/cargo/blob/8814ead110e36ed8fdcf1fdd4009baf82bd78523/doc/book/src/reference/unstable.md?plain=1#L1603-L1626>

## Implementation

### History

| PR | Merged | Title |

|--------|------------|-------------------------------------------------|
| rust-lang#12625 | 2023-10-31 | implement RFC 3127 `-Ztrim-paths` |
| rust-lang#12900 | 2023-10-31 | set env `CARGO_TRIM_PATHS` for build scripts |
| rust-lang#12908 | 2023-11-02 | merge `trim-paths` from different profiles |
| rust-lang#13118 | 2023-12-06 | assert `OSO` and `SO` cannot be trimmed |
| rust-lang#14389 | 2024-08-12 | rustdoc supports trim-paths for diagnostics |
| rust-lang#14908 | 2024-12-09 | use Path::push to construct remap-path-prefix |
| rust-lang#14917 | 2024-12-11 | use stable hash from rustc-stable-hash |
| rust-lang#15614 | 2025-06-02 | remap all paths to `build.build-dir` |
| rust-lang#15621 | 2025-06-02 | enable more tests for windows-msvc |
| rust-lang#16536 | 2026-01-21 | `--remap-path-scope` stabilized in 1.95-nightly
|
| rust-lang#17104 | 2026-06-15 | emit `CARGO_TRIM_PATHS_REMAP` for build.rs |
| rust-lang#17221 | 2026-07-15 | exercise GDB on windows-gnu |
| rust-lang#17302 | 2026-08-03 | unambiguous and reversible remap rules |
| rust-lang#17303 | 2026-08-04 | emit unremap files for final artifacts |
| rust-lang#17326 | 2026-08-07 | exercise unremap files with debuggers |
| rust-lang#17338 | 2026-08-08 | `/cargo/deps` fallback sources |
| rust-lang#17337 | 2026-08-10 | workspace remap under -Zroot-dir |
| rust-lang#17349 | 2026-08-11 | honor workspace prefix override from env |
| rust-lang#17366 | 2026-08-26 | custom workspace-relative member paths remap |
| rust-lang#17424 | 2026-09-02 | remove default scope from release profile |
| rust-lang#17425 | 2026-09-02 | docs: add limitations and polish |
| rust-lang#17432 | 2026-09-04 | limit options to `none\|object\|all` |
| rust-lang#17476 | 2026-09-15 | unremap file in one JSON doc |
| rust-lang#17491 | 2026-09-21 | `build-rs` support |

### Test coverage

* Remap for each dependency kind
* `"object"` with every `split-debuginfo` mode
* `"all"` diagnostics remapping for rustc and rustdoc
* The new build-script environment variables.
* Real world debugger exercises with GDB, LLDB, and CDB
* unremap files with rebuilds, `cargo clean`, JSON messages
* rustc bootstrap workspace prefix override
* `-Zbuild-std` backtraces show `/rustc/<hash>` paths

## Follow-ups after stabilization

* [ ] Revisit reproducibility issues, such as
  * rust-lang#13586
  * rust-lang#15122
  * rust-lang#7645
  * rust-lang#10915
Absolute paths of workspace and `CARGO_HOME` still get into
`-Cmetadata`/`-Cextra-filename`/fingerprints.
With `trim-paths = "object"` we might be able to also trim paths in
those places.
* [ ] Revisit a new default for built-in profiles e.g., `release`
* [ ] In rust-lang/rust stabilize loader logic in
`src/etc/gdb_trim_paths.py` and `src/etc/lldb_trim_paths.py`
* [x] A new issue for `build-rs` adding `CARGO_TRIM_PATHS_SCOPE` and
`CARGO_TRIM_PATHS_REMAP` support
* [ ] A new issue for supporting doctest remapping and documentation
scope.
* [ ] Track unremap files support in artifact dependencies tracking
issue

---

🤖 LLM disclosure: impl history was generated. heading was generated.
meats are human-written.
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