[THRIFT-5364] Remove clippy::vec_box lint override

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Rust - Compiler
• Assignee: Unassigned
• Reporter: Allen George
• Created: 06/Mar/21 14:33
• Updated: 06/Mar/21 16:07

Description

Currently the rust code generator wraps types in a Box in two functions:

1. to_rust_type
2. render_type_sync_read

We do this only when a type is a typedef and ttypedef->is_forward_typedef() == true. This can result in situations where the following thrift (test/Recursive.thrift):

struct RecTree {
  1: list<RecTree> children
  2: i16 item
}

generates the following rust:

#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct RecTree {
  pub children: Option<Vec<Box<RecTree>>>,
  pub item: Option<i16>,
}

Clippy trips this code up with the following error:

/root/.cargo/bin/cargo fmt --all -- --check
/root/.cargo/bin/cargo clippy --all -- -D warnings
    Checking kitchen-sink v0.1.0 (/thrift/src/lib/rs/test)
error: `Vec<T>` is already on the heap, the boxing is unnecessary.
  --> src/recursive.rs:35:24
   |
35 |   pub children: Option<Vec<Box<RecTree>>>,
   |                        ^^^^^^^^^^^^^^^^^ help: try: `Vec<recursive::RecTree>`
   |
   = note: `-D clippy::vec-box` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#vec_box

error: aborting due to previous error

error: could not compile `kitchen-sink`.

This happens because all container elements (Vec,BTreeSet,BTreeMap) are automatically placed on the heap, so a Box is an additional level of indirection.