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feat(trim-paths): set env CARGO_TRIM_PATHS for build scripts - #12900

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feat(trim-paths): set env CARGO_TRIM_PATHS for build scripts#12900
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@weihanglo weihanglo commented Oct 31, 2023

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What does this PR try to resolve?

Set profile options as environment variable CARGO_TRIM_PATHS for build scripts.

As a follow up of #12625.

How should we test and review this PR?

Docs and test should be pretty straightforward.

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r? @ehuss

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@rustbot rustbot added A-build-scripts Area: build.rs scripts A-documenting-cargo-itself Area: Cargo's documentation A-profiles Area: profiles S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 31, 2023
@weihanglo weihanglo mentioned this pull request Oct 31, 2023
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@weihanglo weihanglo added A-trim-paths Area: path sanitization in resulting binaries A-environment-variables Area: environment variables labels Oct 31, 2023
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weihanglo commented Oct 31, 2023

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spurious network error seems like?

Error: failed to read index metadata for crate 'cargo-credential'

Caused by:
0: error sending request for url (https://index.crates.io/ca/rg/cargo-credential): connection error: connection reset
1: connection error: connection reset
2: connection reset

https://github.com/rust-lang/cargo/actions/runs/6706964313/job/18224456440?pr=12900#step:5:552

@bors retry

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 31, 2023
epage
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@weihanglo
weihanglo force-pushed the trim-paths-build-script branch from 0c69592 to 32514c3 Compare October 31, 2023 15:25
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Feel free to r= me whether you make my suggestion or not.

@weihanglo
weihanglo force-pushed the trim-paths-build-script branch from 32514c3 to 2915729 Compare October 31, 2023 16:01
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weihanglo commented Oct 31, 2023

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@bors r=epage

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📌 Commit 2915729 has been approved by epage

It is now in the queue for this repository.

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⌛ Testing commit 2915729 with merge 05cce73...

@weihanglo weihanglo mentioned this pull request Oct 31, 2023
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☀️ Test successful - checks-actions
Approved by: epage
Pushing 05cce73 to master...

@bors
bors merged commit 05cce73 into rust-lang:master Oct 31, 2023
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@bors
Auto merge of rust-lang#117462 - weihanglo:update-cargo, r=weihanglo
9d83ac2 
Update cargo

7 commits in 708383d620e183a9ece69b8fe930c411d83dee27..b4d18d4bd3db6d872892f6c87c51a02999b80802
2023-10-27 21:09:26 +0000 to 2023-10-31 18:19:10 +0000
- refactor(toml): Cleanup noticed on the way to rust-lang/cargo#12801 (rust-lang/cargo#12902)
- feat(trim-paths): set env `CARGO_TRIM_PATHS` for build scripts (rust-lang/cargo#12900)
- feat: implement RFC 3127 `-Ztrim-paths` (rust-lang/cargo#12625)
- docs: clarify config to use vendored source is printed to stdout (rust-lang/cargo#12893)
- Improve the margin calculation for the search command's UI (rust-lang/cargo#12890)
- Add new packages to [workspace.members] automatically (rust-lang/cargo#12779)
- refactor(toml): Decouple parsing from interning system (rust-lang/cargo#12881)

r? ghost
@ehuss ehuss added this to the 1.75.0 milestone Nov 6, 2023
@weihanglo
weihanglo deleted the trim-paths-build-script branch November 28, 2023 20:13
@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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A-build-scripts Area: build.rs scripts A-documenting-cargo-itself Area: Cargo's documentation A-environment-variables Area: environment variables A-profiles Area: profiles A-trim-paths Area: path sanitization in resulting binaries S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion.

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