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Account for gaps in def path table during decoding #79810

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Dec 10, 2020
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Account for gaps in def path table during decoding #79810

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11 changes: 8 additions & 3 deletions compiler/rustc_metadata/src/rmeta/decoder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1553,6 +1553,8 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
return Some(DefId { krate, index: def_index_guess });
}

let is_proc_macro = self.is_proc_macro_crate();

// Slow path: We need to find out the new `DefIndex` of the provided
// `DefPathHash`, if its still exists. This requires decoding every `DefPathHash`
// stored in this crate.
Expand All @@ -1561,9 +1563,12 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
let mut map = FxHashMap::with_capacity_and_hasher(end_id as usize, Default::default());
for i in 0..end_id {
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Late to the party... but if there are gaps, rather than stopping at end_id, do we need to keep iterating until we've processed self.root.tables.def_path_hashes.size() elements?

(Or maybe something more efficient. I'm not familiar with how these tables work.)

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The size() method on Lazy<Table> has a somewhat misleading name - it returns the maximum possible value. So, iterating up to end_id guarnatees that we visit all present entries.

let def_index = DefIndex::from_u32(i);
let hash =
self.root.tables.def_path_hashes.get(self, def_index).unwrap().decode(self);
map.insert(hash, def_index);
// There may be gaps in the encoded table if we're decoding a proc-macro crate
if let Some(hash) = self.root.tables.def_path_hashes.get(self, def_index) {
map.insert(hash.decode(self), def_index);
} else if !is_proc_macro {
panic!("Missing def_path_hashes entry for {:?}", def_index);
}
}
map
});
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