rustdoc `ignore-*` markdown attribute ignores everything

[weihanglo]

Run rustdoc --test lib.rs on aarch64, this doesn't seem to run doctest, while previously it did.

///```ignore-x86_64
///assert!(cfg!(not(target_arch = "x86_64")));
///```
pub fn foo() -> u8 {
    4
}

Steps

$ rustdoc +nightly-2025-03-23 --test lib.rs

running 0 tests

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

$ rustdoc +nightly-2025-03-22 --test lib.rs

running 1 test
test lib.rs - foo (line 2) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.08s

Meta

• Bad version rustdoc 1.87.0-nightly (b48576b4d 2025-03-22)
• Good version rustdoc 1.87.0-nightly (be73c1f46 2025-03-21)

Possibly caused by #138535.

See also rust-lang/cargo#15193 (comment).

[ehuss]

cc @yotamofek @notriddle

[TaKO8Ki]

As a result of the investigation, it appears that this issue is occurring due to changes in how enable-per-target-ignores is handled in this pull request.

When enable-per-target-ignores is not set, it defaults to false. In the previous implementation, this typically matched the arm below and therefore did not ignore the attributes. However, due to the change in conditions, it no longer matches the same arm. If a fix is necessary, the behavior can be reverted to the original by modifying the implementation of that arm.

rust/src/librustdoc/html/markdown.rs

Lines 1203 to 1204 in aa95b96

	LangStringToken::LangToken(x) if x.starts_with("ignore-") => {
	if enable_per_target_ignores {

It matches the following arm in current nightly.

rust/src/librustdoc/html/markdown.rs

Line 1261 in aa8f0fd

LangStringToken::LangToken(x) if let Some(extra) = extra => {

One concern, however, is that the original handling of enable_per_target_ignores might have been incorrect, and the current implementation could be the correct one. Since the option is unstable and its removal is under consideration when it is stabilized, I would like to hear opinions on what kind of implementation would be best for rustdoc.

[yotamofek]

Well, oops. 😅
Thanks for the investigation and sorry for the mess.
I'm traveling and won't have access to a computer until Tuesday at the earliest, so won't be able to file a fix before that.

[TaKO8Ki]

Here is the quick fix for that if necessary. #138877