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Remap def indices for deterministic metadata encoding #162809

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Remap def indices for deterministic metadata encoding #162809

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17 changes: 14 additions & 3 deletions compiler/rustc_hir_id/src/definitions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

use std::fmt::{self, Write};
use std::hash::Hash;
use std::sync::OnceLock;

use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sorted_map::SortedMap;
Expand Down Expand Up @@ -95,6 +96,7 @@ pub struct Definitions {
def_id_to_key: IndexVec<LocalDefId, DefKey>,
// We do only store the local hash, as all the definitions are from the current crate.
def_path_hashes: IndexVec<LocalDefId, Hash64>,
last_deterministic_index: OnceLock<DefIndex>,
def_path_hash_to_index: DefPathToIndexMap,
}

Expand Down Expand Up @@ -292,13 +294,21 @@ pub enum DefPathData {
}

impl Definitions {
/// This function indicates that the order of def id allocations
/// may be non-deterministic after it was called.
pub fn commit_end_of_determinism(&mut self) {
assert!(
self.def_path_hash_to_index.after_parallel_alloc.replace(Default::default()).is_none(),
"this function should be called only once"
)
);

self.last_deterministic_index
.set(
if self.def_id_to_key.is_empty() { 0 } else { self.def_id_to_key.len() - 1 }.into(),

@oli-obk oli-obk Oct 1, 2026 •
edited by rustbot
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will this ever be empty? shouldn't the first entry always be the crate root?

View changes since the review

)
.expect("must be called once");
}

pub fn last_deterministic_index(&self) -> DefIndex {
self.last_deterministic_index.get().copied().expect("must contain index")
}

#[inline(always)]
Expand Down Expand Up @@ -352,6 +362,7 @@ impl Definitions {
def_path_hashes: Default::default(),
def_id_to_key: Default::default(),
def_path_hash_to_index: Default::default(),
last_deterministic_index: Default::default(),
};

// Create the root definition.
Expand Down
10 changes: 8 additions & 2 deletions compiler/rustc_metadata/src/rmeta/decoder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1544,7 +1544,9 @@ impl CrateMetadata {

fn get_proc_macro_quoted_span(&self, tcx: TyCtxt<'_>, index: usize) -> Span {
self.root
.tables
.proc_macro_data
.as_ref()
.unwrap()
.proc_macro_quoted_spans
.get(self, index)
.unwrap_or_else(|| panic!("Missing proc macro quoted span: {index:?}"))
Expand Down Expand Up @@ -1965,8 +1967,12 @@ impl CrateMetadata {
let trait_impls = root
.impls
.decode(&blob)
.map(|trait_impls| (trait_impls.trait_id, trait_impls.impls))
.map(|trait_impls| {
let (krate, index) = trait_impls.trait_id;
((krate, DefIndex::from_u32(index)), trait_impls.impls)
})
.collect();

let alloc_decoding_state =
AllocDecodingState::new(root.interpret_alloc_index.decode(&blob).collect());

Expand Down
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