Implement RFC 3631: add rustdoc doc_cfg features #138907

GuillaumeGomez · 2025-03-24T22:50:33Z

This implementation actually resulted in a lot of simplifications:

All cfg computation is now done in one place: propagate_doc_cfg.rs. Because (trait) impls are not retrieved at the same time as the other items, we cannot perform this computation in the clean process, it needs to be after.
Because there is cfg inheritance, we can keep track of them in one place (in propagate_doc_cfg.rs), meaning we don't need to copy an item's attributes to its children anymore. Only exception: impl items. For them we clone only cfg attributes.
propagate_doc_cfg.rs is also now much simpler, much less need to keep track of parents, since everything we need is handled by the new CfgInfo type.
I also suspect that Cfg::simplify_with could either be removed or at least used directly into propagate_doc_cfg.rs when we compute cfgs. Considering how big the PR already is, I'll do it in a follow-up.

I didn't remove the doc_cfg* features in this PR because some dependencies used in rustc (like stdarch) are using it, so we need to have a nightly released with this PR before I can switch to the new feature.

r? ghost

petrochenkov · 2025-03-25T09:48:06Z

What remains to be done:

I'd also want to block the stabilization on landing #138844 to avoid a stable rustdoc feature relying on externally observable hacks in rustc.
The crater run in #138844 returned mostly clean, so I expect it to land soon.

GuillaumeGomez · 2025-03-25T10:36:45Z

Noted! And that will be a nice improvement, thanks!

Just one thing left for the cfg expansion missing: #[cfg_attr(blabla, derive(Debug))]. In this case, the cfg is not kept in the generated derive items. It's been in my TODO list for a long time now. ^^'

petrochenkov · 2025-03-25T10:49:31Z

Just one thing left for the cfg expansion missing: #[cfg_attr(blabla, derive(Debug))]

Do you mean like in #138515? :)

GuillaumeGomez · 2025-03-25T10:52:03Z

You're my hero! Gonna need to handle this new attribute then. :)

bors · 2025-03-25T17:53:10Z

☔ The latest upstream changes (presumably #138923) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-03-27T19:41:02Z

☔ The latest upstream changes (presumably #138927) made this pull request unmergeable. Please resolve the merge conflicts.

…mease Fix removed version numbers of `doc_auto_cfg` and `doc_cfg_hide` Tracking issue: rust-lang#43781 The `doc_auto_cfg` and `doc_cfg_hide` features were removed in a recent nightly (by rust-lang#138907). I believe that the rustc version numbers at which the features were declared to be removed were incorrect, however, and should both be "1.92" (±1). As evidence in favour of this, the error we get from using this was: ```text error[E0557]: feature has been removed --> src/lib.rs:22:29 | 22 | #![cfg_attr(docsrs, feature(doc_auto_cfg))] | ^^^^^^^^^^^^ feature has been removed | = note: removed in 1.58.0; see <rust-lang#138907> for more information = note: merged into `doc_cfg` ``` Note especially the "removed in 1.58" claim. Further evidence is found in the comment further up this file: https://github.com/rust-lang/rust/blob/4ffeda10e10d4fa0c8edbd0dd9642d8ae7d3e66e/compiler/rustc_feature/src/removed.rs#L49-L53 I've chosen 1.92 as that was the milestone which rust-lang#138907 was added to. cc `@GuillaumeGomez`

rust-lang/rust#138907

Rollup merge of #147123 - DJMcNab:doc_cfg_merge_version, r=fmease Fix removed version numbers of `doc_auto_cfg` and `doc_cfg_hide` Tracking issue: #43781 The `doc_auto_cfg` and `doc_cfg_hide` features were removed in a recent nightly (by #138907). I believe that the rustc version numbers at which the features were declared to be removed were incorrect, however, and should both be "1.92" (±1). As evidence in favour of this, the error we get from using this was: ```text error[E0557]: feature has been removed --> src/lib.rs:22:29 | 22 | #![cfg_attr(docsrs, feature(doc_auto_cfg))] | ^^^^^^^^^^^^ feature has been removed | = note: removed in 1.58.0; see <#138907> for more information = note: merged into `doc_cfg` ``` Note especially the "removed in 1.58" claim. Further evidence is found in the comment further up this file: https://github.com/rust-lang/rust/blob/4ffeda10e10d4fa0c8edbd0dd9642d8ae7d3e66e/compiler/rustc_feature/src/removed.rs#L49-L53 I've chosen 1.92 as that was the milestone which #138907 was added to. cc `@GuillaumeGomez`

…_from_attrs, r=lolbinarycat Remove one loop in `extract_cfg_from_attrs` Follow-up of rust-lang#138907. r? lolbinarycat

This broke CI; see rust-lang/rust#138907.

…_from_attrs, r=lolbinarycat Remove one loop in `extract_cfg_from_attrs` Follow-up of rust-lang#138907. r? lolbinarycat

tarcieri · 2025-09-29T19:56:52Z

compiler/rustc_feature/src/removed.rs

    /// Allows deriving traits as per `SmartPointer` specification
    (removed, derive_smart_pointer, "1.84.0", Some(123430), Some("replaced by `CoercePointee`"), 131284),
+    /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.
+    (removed, doc_auto_cfg, "1.58.0", Some(43781), Some("merged into `doc_cfg`"), 138907),


Is this the correct version? It generates an error message like:

error[E0557]: feature has been removed --> zeroize/src/lib.rs:2:29 | 2 | #![cfg_attr(docsrs, feature(doc_auto_cfg))] | ^^^^^^^^^^^^ feature has been removed | = note: removed in 1.58.0; see <https://github.com/rust-lang/rust/pull/138907> for more information = note: merged into `doc_cfg`

Seems like it was added in 1.58.0, not removed in 1.58.0...

Already fixed by #147123 which is gonna be in the next nightly.

`doc_auto_cfg` was merged into `doc_cfg` in rust-lang/rust#138907

This renames the `doc_auto_cfg` feature, following rust-lang/rust#138907. We install the latest nightly build in CI for docs generation; developers will need to update to at least 2025-09-28.

Rollup merge of #147133 - GuillaumeGomez:rm-loop-extract_cfg_from_attrs, r=lolbinarycat Remove one loop in `extract_cfg_from_attrs` Follow-up of #138907. r? lolbinarycat

…ore-stripping-items, r=lolbinarycat [rustdoc] Move doc cfg propagation pass before items stripping passes Follow-up of rust-lang#138907. r? lolbinarycat

Rollup merge of #147153 - GuillaumeGomez:doc-propagation-before-stripping-items, r=lolbinarycat [rustdoc] Move doc cfg propagation pass before items stripping passes Follow-up of #138907. r? lolbinarycat

``` error[E0557]: feature has been removed --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/socket2-0.6.0/src/lib.rs:57:29 | 57 | #![cfg_attr(docsrs, feature(doc_auto_cfg))] | ^^^^^^^^^^^^ feature has been removed | = note: removed in CURRENT_RUSTC_VERSION; see <rust-lang/rust#138907> for more information = note: merged into `doc_cfg` ```

Nightly fails due to a dependency: ``` error[E0557]: feature has been removed --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/socket2-0.6.0/src/lib.rs:57:29 | 57 | #![cfg_attr(docsrs, feature(doc_auto_cfg))] | ^^^^^^^^^^^^ feature has been removed | = note: removed in CURRENT_RUSTC_VERSION; see <rust-lang/rust#138907> for more information = note: merged into `doc_cfg` ```

`doc_auto_cfg` has been removed in the latest nightly, see rust-lang/rust#138907. This feature was merged into `doc_cfg`. This fixes the rustdoc build in the latest nightly toolchain with docsrs feature enabled.