ICE on rustdoc-json with re-export due to ID collision

[aDotInTheVoid]

Code

mod inner {
    pub struct Public;
}
pub use inner::Public as Reexported;

Meta

Invoke with rustdoc broke.rs --output-format json

rustdoc --version --verbose:

rustdoc 1.51.0-nightly (fde692739 2021-01-02)
binary: rustdoc
commit-hash: fde692739576089729885b7f79aa2232cb9778c5
commit-date: 2021-01-02
host: x86_64-apple-darwin
release: 1.51.0-nightly

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Item { id: Id("0:4"), crate_id: 0, name: Some("Reexported"), source: Some(Span { filename: "broke.rs", begin: (2, 4), end: (2, 22) }), visibility: Public, docs: "", links: {}, attrs: [], deprecation: None, kind: Struct, inner: StructItem(Struct { struct_type: Unit, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [], impls: [Id("0:9"), Id("0:10"), Id("0:11"), Id("0:13"), Id("0:14")] }) }`,
 right: `Item { id: Id("0:4"), crate_id: 0, name: Some("Public"), source: Some(Span { filename: "broke.rs", begin: (2, 4), end: (2, 22) }), visibility: Public, docs: "", links: {}, attrs: [], deprecation: None, kind: Struct, inner: StructItem(Struct { struct_type: Unit, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [], impls: [Id("0:9"), Id("0:10"), Id("0:11"), Id("0:13"), Id("0:14")] }) }`', src/librustdoc/json/mod.rs:167:17

Backtrace

RUST_BACKTRACE=1 rustdoc broke.rs --output-format json
thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Item { id: Id("0:4"), crate_id: 0, name: Some("Reexported"), source: Some(Span { filename: "broke.rs", begin: (2, 4), end: (2, 22) }), visibility: Public, docs: "", links: {}, attrs: [], deprecation: None, kind: Struct, inner: StructItem(Struct { struct_type: Unit, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [], impls: [Id("0:9"), Id("0:10"), Id("0:11"), Id("0:13"), Id("0:14")] }) }`,
 right: `Item { id: Id("0:4"), crate_id: 0, name: Some("Public"), source: Some(Span { filename: "broke.rs", begin: (2, 4), end: (2, 22) }), visibility: Public, docs: "", links: {}, attrs: [], deprecation: None, kind: Struct, inner: StructItem(Struct { struct_type: Unit, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [], impls: [Id("0:9"), Id("0:10"), Id("0:11"), Id("0:13"), Id("0:14")] }) }`', src/librustdoc/json/mod.rs:167:17
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <rustdoc::json::JsonRenderer as rustdoc::formats::renderer::FormatRenderer>::item
   3: rustdoc::formats::renderer::run_format
   4: rustdoc::run_renderer
   5: rustc_session::utils::<impl rustc_session::session::Session>::time
   6: rustc_interface::passes::QueryContext::enter
   7: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
   8: rustc_span::with_source_map
   9: rustc_interface::interface::create_compiler_and_run
  10: rustdoc::main_options
  11: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

error: Unrecognized option: 'output-format'

Working variants

mod inner { pub struct Public; }
use inner::Public as Reexported;

json

{
    "root": "0:0",
    "crate_version": null,
    "includes_private": false,
    "index": {
        "0:0": {
            "id": "0:0",
            "inner": {
                "is_crate": true,
                "items": []
            },
            "kind": "module",
            "name": "work1",
            "visibility": "public"
        }
    },
    "paths": {
        "0:0": {
            "crate_id": 0,
            "path": ["work1"],
            "kind": "module"
        }
    },
    "external_crates": {},
    "format_version": 1
}

mod inner { pub struct Public; }
pub use inner::Public;

json

{
    "root": "0:0",
    "crate_version": null,
    "includes_private": false,
    "index": {
        "0:0": {
            "id": "0:0",
            "inner": {
                "is_crate": true,
                "items": ["0:4"]
            },
            "kind": "module",
            "name": "work2",
            "visibility": "public"
        },
        "0:4": {
            "id": "0:4",
            "inner": {
                "struct_type": "unit",
                "generics": {
                    "params": [],
                    "where_predicates": []
                },
                "fields_stripped": false,
                "fields": [],
                "impls": ["0:9", "0:10", "0:11", "0:13", "0:14"]
            },
            "kind": "struct",
            "name": "Public",
            "visibility": "public"
        }
    },
    "paths": {
        "0:4": {
            "crate_id": 0,
            "path": ["work2", "Public"],
            "kind": "struct"
        },
        "0:0": {
            "crate_id": 0,
            "path": ["work2"],
            "kind": "module"
        }
    },
    "external_crates": {},
    "format_version": 1
}

pub mod inner { pub struct Public; }
pub use inner::Public as Reexported;

json

{
    "root": "0:0",
    "crate_version": null,
    "includes_private": false,
    "index": {
        "0:6": {
            "id": "0:6",
            "inner": {
                "span": "inner::Public",
                "name": "Reexported",
                "id": "0:4",
                "glob": false
            },
            "kind": "import",
            "name": null,
            "visibility": "public"
        },
        "0:3": {
            "id": "0:3",
            "inner": {
                "is_crate": false,
                "items": ["0:4"]
            },
            "kind": "module",
            "name": "inner",
            "visibility": "public"
        },
        "0:0": {
            "id": "0:0",
            "inner": {
                "is_crate": true,
                "items": ["0:6", "0:3"]
            },
            "kind": "module",
            "name": "work3",
            "visibility": "public"
        },
        "0:4": {
            "id": "0:4",
            "inner": {
                "struct_type": "unit",
                "generics": {
                    "params": [],
                    "where_predicates": []
                },
                "fields_stripped": false,
                "fields": [],
                "impls": ["0:9", "0:10", "0:11", "0:13", "0:14"]
            },
            "kind": "struct",
            "name": "Public",
            "visibility": "public"
        }
    },
    "paths": {
        "0:4": {
            "crate_id": 0,
            "path": ["work3", "inner", "Public"],
            "kind": "struct"
        },
        "0:3": {
            "crate_id": 0,
            "path": ["work3", "inner"],
            "kind": "module"
        },
        "0:0": {
            "crate_id": 0,
            "path": ["work3"],
            "kind": "module"
        }
    },
    "external_crates": {},
    "format_version": 1
}

Whats happening

The panic is here

rust/src/librustdoc/json/mod.rs

Lines 163 to 169 in db69136

	let removed = self.index.borrow_mut().insert(id.into(), new_item.clone());
	// FIXME(adotinthevoid): Currently, the index is duplicated. This is a sanity check
	// to make sure the items are unique.
	if let Some(old_item) = removed {
	assert_eq!(old_item, new_item);
	}
	}

inner::Public is being added to the index when is shouldn't (I think), so when Reexported is added, the IDs colide, and we bail.

I think the solution is that inner::Public should never have been added into the index.

• Related comment: Rustdoc: Use correct def_id for doctree::Import #79751 (comment)
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[aDotInTheVoid]

@rustbot modify labels: -T-compiler +T-rustdoc

[jyn514]

I still think the right fix for this is for JSON to have its own IDs that are separate from DefIds. The main issue is that you want the functionality of both HirIds and DefIds, basically, and some things with the same DefId have different HirIds. You can't just use HirIds because they're only available for the current crate; you wouldn't be able to serialize things from other crates.

[aDotInTheVoid]

@rustbot modify labels +A-rustdoc-json