derive helpers not in `attrs` field in rustdoc json

[SwishSwushPow]

Problem

This regression has been noticed when running the integration test of BuFFI after updating the toolchain from Rust 1.95.0 to 1.96.0.

For the functionality of BuFFI we rely on attribute information being provided in the output of rustdoc json which we parse using rustdoc-types. We are aware that this json output is unstable and we usually can adjust our side to keep track, but this time the version of rustdoc-types has not changed, yet it seems that some attribute information that was provided as part of Item objects seems to have vanished completely. After checking it I can confirm that it is not showing up in the rustdoc json output anymore.

Code

We have this enum in the example for BuFFI and we rely on the attributes to generate the correct FFI code.

#[derive(serde::Serialize, serde::Deserialize)]
pub enum RandomEnum {
    /// An empty case that is here to make the test simpler
    NoValue,
    /// A timestamp from chrono that we would like to use in the API
    TimeStamp(#[serde(with = "crate::DateTimeHelper")] DateTime<Utc>),
}

I have chosen this example because it is the point where the test currently fails. There are more types in the example that show the various ways how we make use of attributes. If necessary I can provide a smaller example where it is also visible that the attributes are not part of the rustdoc json anymore.

If we have a look at the case TimeStamp, we want to have information about the serde attribute.

After parsing the generated json with rustdoc-types and resolving it partially, before we had

...
attrs: [
    Other(
        "#[serde(with = \"crate::DateTimeHelper\")]",
    ),
],
...

dbg! output on 1.95.0

[buffi/src/lib.rs:1486:29] &t = Item {
    id: Id(
        126,
    ),
    crate_id: 0,
    name: Some(
        "0",
    ),
    span: Some(
        Span {
            filename: "example/buffi_example/src/lib.rs",
            begin: (
                69,
                56,
            ),
            end: (
                69,
                69,
            ),
        },
    ),
    visibility: Default,
    docs: None,
    links: {},
    attrs: [
        Other(
            "#[serde(with = \"crate::DateTimeHelper\")]",
        ),
    ],
    deprecation: None,
    inner: StructField(
        ResolvedPath(
            Path {
                path: "chrono::DateTime",
                id: Id(
                    94,
                ),
                args: Some(
                    AngleBracketed {
                        args: [
                            Type(
                                ResolvedPath(
                                    Path {
                                        path: "chrono::Utc",
                                        id: Id(
                                            95,
                                        ),
                                        args: None,
                                    },
                                ),
                            ),
                        ],
                        constraints: [],
                    },
                ),
            },
        ),
    ),
}

while now we get

...
attrs: [],
...

dbg! output on 1.96.0 (note the empty `attrs` field)

[buffi/src/lib.rs:1486:29] &t = Item {
    id: Id(
        126,
    ),
    crate_id: 0,
    name: Some(
        "0",
    ),
    span: Some(
        Span {
            filename: "example/buffi_example/src/lib.rs",
            begin: (
                69,
                56,
            ),
            end: (
                69,
                69,
            ),
        },
    ),
    visibility: Default,
    docs: None,
    links: {},
    attrs: [],
    deprecation: None,
    inner: StructField(
        ResolvedPath(
            Path {
                path: "chrono::DateTime",
                id: Id(
                    94,
                ),
                args: Some(
                    AngleBracketed {
                        args: [
                            Type(
                                ResolvedPath(
                                    Path {
                                        path: "chrono::Utc",
                                        id: Id(
                                            95,
                                        ),
                                        args: None,
                                    },
                                ),
                            ),
                        ],
                        constraints: [],
                    },
                ),
            },
        ),
    ),
}

Using cargo-bisect-rustc I was able to narrow down the problem to this commit eb9d3ca.

I think the relevat PR could be #153540.

Version it worked on

It most recently worked on: Rust 1.95.0

Version with regression

rustc --version --verbose:

rustc 1.96.0 (ac68faa20 2026-05-25)
binary: rustc
commit-hash: ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96
commit-date: 2026-05-25
host: aarch64-apple-darwin
release: 1.96.0
LLVM version: 22.1.2

Pinging @aDotInTheVoid (we briefly chatted about BuFFI and its use of rustdoc json before) and @scrabsha (author of the PR listed above) because I think they could be interested in the regression and might be best suited to answer if that is intended or not. I hope that is ok. 😅

@rustbot modify labels: +regression-from-stable-to-stable -regression-untriaged

[scrabsha]

oh, i did not know derive helpers were exposed in rustdoc-json in the first place. my PR is indeed the culprit.