extracted doctests that have `include!` macros cannot be compiled outside of rustdoc

[TroyKomodo]

Code

Consider the following code

/// ```rust
/// const MY_STRING: &str = include_str!("my_file.txt");
/// ```
fn f() {}

If you run rustdoc to extract the tests you get something like this

cargo build

RUSTC_BOOTSTRAP=1 rustdoc \                                                                                                                             
    -Zunstable-options \
    --crate-name=a \
    --edition 2024 \
    --output-format doctest \
    --crate-type lib a/src/lib.rs \
    --extern=a=target/debug/liba.rlib \
    -Ltarget/debug \
    -Ltarget/debug/deps

{
  "format_version": 1,
  "doctests": [
    {
      "file": "a/src/lib.rs",
      "line": 1,
      "doctest_attributes": {
        "original": "rust",
        "should_panic": false,
        "no_run": false,
        "ignore": "None",
        "rust": true,
        "test_harness": false,
        "compile_fail": false,
        "standalone_crate": false,
        "error_codes": [],
        "edition": null,
        "added_css_classes": [],
        "unknown": []
      },
      "original_code": "const MY_STRING: &str = include_str!(\"my_file.txt\");",
      "doctest_code": "#![allow(unused)]\nfn main() {\nconst MY_STRING: &str = include_str!(\"my_file.txt\");\n}",
      "name": "a/src/lib.rs - f (line 1)"
    }
  ]
}

I observed the behaviour of the 2024 merged doc tests but it still seems that somehow rustdoc is using internal features to tell rustc where the src file is relative to so that include! and include_str! resolve.

Version

rustdoc 1.88.0 (6b00bc388 2025-06-23)
binary: rustdoc
commit-hash: 6b00bc3880198600130e1cf62b8f8a93494488cc
commit-date: 2025-06-23
host: x86_64-unknown-linux-gnu
release: 1.88.0
LLVM version: 20.1.5

Additional Details

Part of my working goal to get bazel project working without cargo.

[TroyKomodo]

maybe related to #143943 (comment)

[TroyKomodo]

These env vars.

Perhaps this should be added to rustc's unstable features documentation about stdin files.

UNSTABLE_RUSTDOC_TEST_LINE: -1
UNSTABLE_RUSTDOC_TEST_PATH: test.rs