cfg(docsrs) isn't being set properly?

[CAD97]

Example:

#[cfg(docsrs)]
compile_error!("cfg(docsrs) set");

#[cfg(not(docsrs))]
compile_error!("cfg(docsrs) not set");

> cargo +nightly docs-rs --verbose
       Dirty cstr8 v0.1.3 (D:\git\cad97\cstr8): the precalculated components changed
 Documenting cstr8 v0.1.3 (D:\git\cad97\cstr8)
     Running `rustdoc --edition=2021 --crate-type lib --crate-name cstr8 src\lib.rs -o D:\.rust\target\doc --cfg "feature=\"alloc\"" --cfg "feature=\"default\"" --cfg "feature=\"std\"" --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 -C metadata=2fab72609bfd58bc -L dependency=D:\.rust\target\debug\deps --crate-version 0.1.3`
error: cfg(docsrs) not set
  --> src\lib.rs:28:1
   |
28 | compile_error!("cfg(docsrs) not set");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not document `cstr8`

> $env.RUSTDOCFLAGS = "--cfg=docsrs"
> cargo +nightly doc --verbose
       Dirty cstr8 v0.1.3 (D:\git\cad97\cstr8): the profile configuration changed
 Documenting cstr8 v0.1.3 (D:\git\cad97\cstr8)
     Running `rustdoc --edition=2021 --crate-type lib --crate-name cstr8 src\lib.rs -o D:\.rust\target\doc --cfg "feature=\"alloc\"" --cfg "feature=\"default\"" --cfg "feature=\"std\"" --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 -C metadata=6c16e02dedfb218b -L dependency=D:\.rust\target\debug\deps --cfg=docsrs --crate-version 0.1.3`
error: cfg(docsrs) set
  --> src\lib.rs:25:1
   |
25 | compile_error!("cfg(docsrs) set");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not document `cstr8`

> cargo +nightly docs-rs --version
cargo-docs-rs 0.1.10

Attempting to diagnose, this seems to be caused by -Zhost-config, as removing that flag from the execution results in --cfg=docsrs being included in the rustdoc invocation.

> cargo +nightly rustdoc --verbose -Zunstable-options --config 'build.rustdocflags=["--cfg=docsrs"]' -Ztarget-applies-to-host
       Dirty cstr8 v0.1.3 (D:\git\cad97\cstr8): the rustflags changed
 Documenting cstr8 v0.1.3 (D:\git\cad97\cstr8)
     Running `rustdoc --edition=2021 --crate-type lib --crate-name cstr8 src\lib.rs -o D:\.rust\target\doc --cfg "feature=\"alloc\"" --cfg "feature=\"default\"" --cfg "feature=\"std\"" --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 -C metadata=2fab72609bfd58bc -L dependency=D:\.rust\target\debug\deps --cfg=docsrs --crate-version 0.1.3`
error: cfg(docsrs) set
  --> src\lib.rs:25:1
   |
25 | compile_error!("cfg(docsrs) set");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> cargo +nightly rustdoc --verbose -Zunstable-options --config 'build.rustdocflags=["--cfg=docsrs"]' -Ztarget-applies-to-host -Zhost-config
       Dirty cstr8 v0.1.3 (D:\git\cad97\cstr8): the config settings changed
 Documenting cstr8 v0.1.3 (D:\git\cad97\cstr8)
     Running `rustdoc --edition=2021 --crate-type lib --crate-name cstr8 src\lib.rs -o D:\.rust\target\doc --cfg "feature=\"alloc\"" --cfg "feature=\"default\"" --cfg "feature=\"std\"" --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=119 -C metadata=2fab72609bfd58bc -L dependency=D:\.rust\target\debug\deps --crate-version 0.1.3`
error: cfg(docsrs) not set
  --> src\lib.rs:28:1
   |
28 | compile_error!("cfg(docsrs) not set");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> cargo +nightly -Vv
cargo 1.78.0-nightly (f772ec022 2024-03-01)
release: 1.78.0-nightly
commit-hash: f772ec0224d3755ce52ac5128a80319fb2eb45d0
commit-date: 2024-03-01
host: x86_64-pc-windows-msvc
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.6.0-DEV (sys:0.4.72+curl-8.6.0 vendored ssl:Schannel)
os: Windows 10.0.22631 (Windows 11 Education) [64-bit]

That might mean this is an upstream issue but I legitimately don't know and this is where I ran into it.

[CAD97]

I can now confirm that this is an issue with cargo-docs-rs and not with docs-rs itself, as the just published cstr8 docs use cfg(docsrs) to turn on doc_auto_cfg which is showing up in the rendered docs. So there's a difference somewhere.