Doctests should not inherit features

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Code

Have a crate that

has feature(s), like with Cargo.toml:

❯ cat Cargo.toml 
 [package]
 name = "macro_def"
 version = "0.1.0"
 edition = "2024"
  
 [dependencies]
  
 [features]
 macro_def_cfg = []

exports a macro_rules! that (incorrectly, of course) generates code conditional on such feature(s), like

   #[macro_export]
   macro_rules! generate_unknown_cfg {
     () => {
         #[cfg(feature="macro_def_cfg")]
         let _ = {};
      }
   }

have a doctest in that crate

containing #![forbid(unexpected_cfgs)] (or a deny), and

invoking that macro

/// ```
/// #![forbid(unexpected_cfgs)]
///
/// use macro_def::generate_unknown_cfg;
///
/// let _: () = {
///     generate_unknown_cfg!();
/// };
/// ```

OR, if the doctest itself doesn't define forbid or deny, then have the crate's src/lib.rs contain: #![doc(test(attr(forbid(unexpected_cfgs))))] (or a deny)


```
Reproduction Steps
cargo test
Expected Outcome
---- src/lib.rs - generate_unknown_cfg (line 3) stdout ----
error: unexpected `cfg` condition value: `macro_def_cfg`
 --> src/lib.rs:8:5
  |
8 |     generate_unknown_cfg!();
  |     ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: no expected values for `feature`

---- YES, expecting NO features to be inherited from the crate
  = note: using a cfg inside a macro will use the cfgs from the destination crate and not the ones from the defining crate
  = help: try referring to `generate_unknown_cfg` crate for guidance on how handle this unexpected cfg
  = help: the macro `generate_unknown_cfg` may come from an old version of the `macro_def` crate, try updating your dependency with `cargo update -p macro_def`
  = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
note: the lint level is defined here
 --> src/lib.rs:1:11
  |
1 | #![forbid(unexpected_cfgs)]

Expecting this error, because as https://doc.rust-lang.org/nightly/rustdoc/write-documentation/the-doc-attribute.html#testno_crate_inject clearly implies that doctests are build in a separate crate. PLUS, since doctests can't test non-public functionality, they shouldn't inherit any features at all.
Actual Output
Compiles fine - so it hides the error in the macro.
Version
1.89.0 (and probably also older); 1.91.1; and December 1, 2025 nightly

Reproduce the issue from the shown Cargo.toml and src/lib.rs example by running cargo test. Trace how the doctest crate receives feature configuration when it invokes the exported macro, and compare that with the expected unexpected_cfgs diagnostic. Done means the doctest no longer inherits the defining crate's features and reports the expected lint error.

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Doctests should not inherit features

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