rustc-dev-guide: Mention --extern modifiers for aux-crate directive

Author: Enselic

src/tests/compiletest.md

@@ -655,7 +655,9 @@ to link to the extern crate to make the crate be available as an extern prelude.
 That allows you to specify the additional syntax of the `--extern` flag, such as
 renaming a dependency. For example, `//@ aux-crate:foo=bar.rs` will compile
 `auxiliary/bar.rs` and make it available under then name `foo` within the test.
-This is similar to how Cargo does dependency renaming.
+This is similar to how Cargo does dependency renaming. It is also possible to
+specify [`--extern` modifiers](https://github.com/rust-lang/rust/issues/98405).
+For example, `//@ aux-crate:noprelude:foo=bar.rs`.
 
 `aux-bin` is similar to `aux-build` but will build a binary instead of a
 library. The binary will be available in `auxiliary/bin` relative to the working

src/tests/directives.md

@@ -53,14 +53,14 @@ Directives can generally be found by browsing the
 
 See [Building auxiliary crates](compiletest.html#building-auxiliary-crates)
 
-| Directive             | Explanation                                                                                           | Supported test suites                  | Possible values                               |
-|-----------------------|-------------------------------------------------------------------------------------------------------|----------------------------------------|-----------------------------------------------|
-| `aux-bin`             | Build a aux binary, made available in `auxiliary/bin` relative to test directory                      | All except `run-make`/`run-make-cargo` | Path to auxiliary `.rs` file                  |
-| `aux-build`           | Build a separate crate from the named source file                                                     | All except `run-make`/`run-make-cargo` | Path to auxiliary `.rs` file                  |
-| `aux-crate`           | Like `aux-build` but makes available as extern prelude                                                | All except `run-make`/`run-make-cargo` | `<extern_prelude_name>=<path/to/aux/file.rs>` |
-| `aux-codegen-backend` | Similar to `aux-build` but pass the compiled dylib to `-Zcodegen-backend` when building the main file | `ui-fulldeps`                          | Path to codegen backend file                  |
-| `proc-macro`          | Similar to `aux-build`, but for aux forces host and don't use `-Cprefer-dynamic`[^pm].                | All except `run-make`/`run-make-cargo` | Path to auxiliary proc-macro `.rs` file       |
-| `build-aux-docs`      | Build docs for auxiliaries as well.  Note that this only works with `aux-build`, not `aux-crate`.     | All except `run-make`/`run-make-cargo` | N/A                                           |
+| Directive             | Explanation                                                                                           | Supported test suites                  | Possible values                                                    |
+|-----------------------|-------------------------------------------------------------------------------------------------------|----------------------------------------|--------------------------------------------------------------------|
+| `aux-bin`             | Build a aux binary, made available in `auxiliary/bin` relative to test directory                      | All except `run-make`/`run-make-cargo` | Path to auxiliary `.rs` file                                       |
+| `aux-build`           | Build a separate crate from the named source file                                                     | All except `run-make`/`run-make-cargo` | Path to auxiliary `.rs` file                                       |
+| `aux-crate`           | Like `aux-build` but makes available as extern prelude                                                | All except `run-make`/`run-make-cargo` | `[<extern_modifiers>:]<extern_prelude_name>=<path/to/aux/file.rs>` |
+| `aux-codegen-backend` | Similar to `aux-build` but pass the compiled dylib to `-Zcodegen-backend` when building the main file | `ui-fulldeps`                          | Path to codegen backend file                                       |
+| `proc-macro`          | Similar to `aux-build`, but for aux forces host and don't use `-Cprefer-dynamic`[^pm].                | All except `run-make`/`run-make-cargo` | Path to auxiliary proc-macro `.rs` file                            |
+| `build-aux-docs`      | Build docs for auxiliaries as well.  Note that this only works with `aux-build`, not `aux-crate`.     | All except `run-make`/`run-make-cargo` | N/A                                                                |
 
 [^pm]: please see the [Auxiliary proc-macro section](compiletest.html#auxiliary-proc-macro) in the compiletest chapter for specifics.