Auto merge of #155307 - Urgau:rustdoc-stabilize-remap-path-prefix, r=GuillaumeGomez

Stabilize `--remap-path-prefix` in rustdoc



# Stabilization report of  `--remap-path-prefix` in rustdoc

## Summary

`rustc` supports remapping source paths prefixes as a best effort in all compiler generated output, including compiler diagnostics, debugging information, macro expansions, documentation, doctests, etc.

This is useful for normalizing build products, for example, by removing the current directory out of the paths emitted into object files.

This stabilization stabilize the same flag used by `rustc` in `rustdoc`.

There are no tracking issue.

Stabilization was discussed at the last meeting, [#t-rustdoc/meetings > 2026-04-13 @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/393423-t-rustdoc.2Fmeetings/topic/2026-04-13/near/585264347).

### What is stabilized

The rustdoc `--remap-path-prefix` flag is being stabilized by this PR. (It's equivalent to rustc flag)

It permits remapping (as a best effort) source path prefixes in all output, including diagnostics, debug information, macro expansions, generated documentation, etc.

It takes a value of the form `FROM=TO` where a path prefix equal to `FROM` is rewritten to the value `TO`.

#### Example

```sh
rustdoc src/lib.rs --remap-path-prefix="$PWD=/foo"
```

### What isn't stabilized

Neither `--remap-path-scope` (~~soon to be added as unstable in `rustdoc`~~ https://github.com/rust-lang/rust/issues/155451) or the already unstable in `rustc` `documentation` scope are being stabilized or added here.

## Design

### Implementation history

- rust-lang/rust#107099

### Unresolved questions

There are no unresolved questions.

### Post-implementation changes

The implementation has evolved with `rustc`, but no changes to the flag it-self have been made.

### Nightly extensions

The `documentation` scope, which currently can only be set from `rustc`, as we need to add an equivalent to the `--remap-path-scope` flag, ~~which is planned~~ (EDIT: https://github.com/rust-lang/rust/issues/155451), but not required, the current `--remap-path-prefix` defaults to the `all` scope, like `rustc`.

### Doors closed

We are committing to having to having a flag that permits remapping paths. The compiler team already made the same commitment.

## Feedback

### Call for testing

No call for testing has been done.

### Nightly use

Unable to determine. A [GitHub search](https://github.com/search?q=%20%2F--remap-path-prefix%2F&type=code) only seems to only reveals the `rustc` usage (over 6k though).

Rust-for-Linux is using the [flag](https://github.com/torvalds/linux/blob/e80d033851b3bc94c3d254ac66660ddd0a49d72c/Makefile#L1151-L1153).

## Implementation

### Major parts

- rust-lang/rust#107099
- rust-lang/rust#149709
- rust-lang/rust#150172
- rust-lang/rust#151589

### Coverage

- [`tests/rustdoc-ui/remap-path-prefix-failed-doctest-output.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-ui/remap-path-prefix-failed-doctest-output.rs)
- [`tests/rustdoc-ui/remap-path-prefix-invalid-doctest.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-ui/remap-path-prefix-invalid-doctest.rs)
- [`tests/rustdoc-ui/remap-path-prefix-macro.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-ui/remap-path-prefix-macro.rs)
- [`tests/rustdoc-ui/remap-path-prefix-passed-doctest-output.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-ui/remap-path-prefix-passed-doctest-output.rs)
- [`tests/rustdoc-ui/lints/remap-path-prefix-lint.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-ui/lints/remap-path-prefix-lint.rs)
- [`tests/rustdoc-html/import-remapped-paths.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-html/import-remapped-paths.rs)
- [`tests/rustdoc-html/macro/external-macro-src.rs`](https://github.com/rust-lang/rust/blob/12f35ad39ed3e39df4d953c46d4f6cc6c82adc96/tests/rustdoc-html/macro/external-macro-src.rs)

### Outstanding bugs

There are no outstanding bugs regarding `--remap-path-prefix` in `rustdoc`.

There are [caveats and limitation](https://doc.rust-lang.org/nightly/rustc/remap-source-paths.html#caveats-and-limitations) in `rustc`, but they mostly concern generated object files, which we don't really have. 

### Outstanding FIXMEs

There are no FIXME regarding `--remap-path-prefix`.

## Acknowledgments

- @edward-shen
- @Urgau