paritytech / paritytech/parity-common

Infinite recursion on BoundedVec

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Dominant language
Rust
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Description

When using bounded-collections v0.2.4, I get this error when compiling the runtime:

error: reached the recursion limit while instantiating `decode_vec_with_len::<(sp_runtime::Vec<u8>, sp_runtime::Vec<u8>), ...>`
      --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/parity-scale-codec-3.7.4/src/codec.rs:1228:34
       |
  1228 |             .and_then(move |Compact(len)| decode_vec_with_len(input, len as usize))
       |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
  note: `decode_vec_with_len` defined here
      --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/parity-scale-codec-3.7.4/src/codec.rs:1196:1
       |
  1196 | / pub fn decode_vec_with_len<T: Decode, I: Input>(
  1197 | |     input: &mut I,
  1198 | |     len: usize,
  1199 | | ) -> Result<Vec<T>, Error> {
       | |__________________________^
       = note: the full type name has been written to '/path/long-type.txt'
error: reached the recursion limit while instantiating `decode_vec_with_len::<MultiAsset, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, ...>>>>>`
      --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bounded-collections-0.2.4/src/bounded_vec.rs:279:15
       |
  279  |         let inner = decode_vec_with_len(input, len as usize)?;
       |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
  note: `decode_vec_with_len` defined here
      --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/parity-scale-codec-3.7.4/src/codec.rs:1196:1
       |
  1196 | / pub fn decode_vec_with_len<T: Decode, I: Input>(
  1197 | |     input: &mut I,
  1198 | |     len: usize,
  1199 | | ) -> Result<Vec<T>, Error> {
       | |__________________________^
       = note: the full type name has been written to 'path.long-type.txt'
error: could not compile `enjin-matrix-runtime` (lib) due to 2 previous errors
Process finished with exit code 101

The contents of the mentioned long-type file are this:

decode_vec_with_len::<(sp_runtime::Vec<u8>, sp_runtime::Vec<u8>), sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, sp_core::bounded_collections::bounded_btree_map::PrependCompactInput<'_, 
// the above repeats maybe a hundred times
codec::codec::BytesCursor>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

The runtime compiles correctly when I patch bounded-collections to v0.2.3. I have the recursion limit set to 256. It seems to be an issue with BoundedVec, but it mentions sp_core::bounded_collections::bounded_btree_map::PrependCompactInput, so not sure.

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Research direction

Start by comparing bounded-collections 0.2.3 and 0.2.4 at bounded_vec.rs:279, then inspect parity-scale-codec's codec.rs around lines 1196 and 1228. Reproduce the runtime compilation with recursion_limit set to 256 and use the generated long-type file to trace the nested PrependCompactInput types. Done means the reported runtime compiles with bounded-collections 0.2.4 without reaching the recursion limit.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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