`rustdoc --test` doesn't recognize register_tool

[zjp-CN]

I tried this code:

// lib.rs
#[rapx::tag]
fn f() {}

# ✅ This compiles and generates doc/
$ rustdoc lib.rs -Zcrate-attr="feature(register_tool)" -Zcrate-attr="register_tool(rapx)"

# 💥This doesn't compile
$ rustdoc --test lib.rs -Zcrate-attr="feature(register_tool)" -Zcrate-attr="register_tool(rapx)"
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `rapx`
 --> lib.rs:1:3
  |
1 | #[rapx::tag]
  |   ^^^^ use of unresolved module or unlinked crate `rapx`

I expected to see this happen: rust --test will recognize register_tool as rustdoc does.

Instead, this happened: rust --test doesn't recognize register_tool.

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (45acf54ee 2025-06-16)
binary: rustc
commit-hash: 45acf54eea118ed27927282b5e0bfdcd80b7987c
commit-date: 2025-06-16
host: aarch64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

[zjp-CN]

Note this compiles:

#![feature(register_tool)]
#![register_tool(rapx)]
#[rapx::tag]
fn f() {}

$ rustdoc --test lib.rs

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

[fmease]

We don't copy over any attributes from the host crate to the generated test crates and we can't blindly copy over all them at least not backward compatibly. We might want to allowlist some but that's feature request territory.

Workaround / solution: Also add: -Zcrate-attr=doc(test(attr(feature(register_tool), register_tool(rapx)))).

[zjp-CN]

Thx for the explanation.

Workaround / solution: Also add: -Zcrate-attr=doc(test(attr(feature(register_tool), register_tool(rapx)))).

How does it work? The following commands still failed to know rapx tool attr.

$ rustdoc --test lib.rs -Zcrate-attr="doc(test(attr(feature(register_tool), register_tool(rapx))))"
$ rustdoc --test lib.rs -Zcrate-attr="doc(test(attr(feature(register_tool), register_tool(rapx))))" -Zcrate-attr="feature(register_tool)" -Zcrate-attr="register_tool(rapx)"

error[E0433]: failed to resolve: use of unresolved module or unlinked crate `rapx`
 --> lib.rs:1:3
  |
1 | #[rapx::tag]
  |   ^^^^ use of unresolved module or unlinked crate `rapx`

Edit: it indeed doesn't work, cc rust-lang/rfcs#3791 (comment)

[zjp-CN]

We might want to allowlist some but that's feature request territory.

I think it has been specified in RFC#3791#crate-attr#doctests.

• cc RFC: --crate-attr rfcs#3791
• cc #![register_{attribute,lint}_tool] rfcs#3808

Edit:

• Oops, I think this is a duplicate of rustdoc --test does not respect -Zcrate-attr #138491