refactor: handle impls correctly by moving instead of dropping them

[ahomescu]

_{Stack created with GitHub Stacks CLI • Give Feedback 💬}

[thedataking]

Review of stack 1953: two compile regressions in deferred impl handling, reproduced with compiling inputs and compared against the earlier transform.

[thedataking]

[P2] Account for deferred impls when merging their self types

Pending impls bypass the declaration deduplication logic and are all appended after path_mapping has unified their self types. If two equivalent header types each have two const-only impl blocks, the first impl is carried and deduplicated with the type, but both copies of the second impl are appended to the same resulting type. The output then fails with E0592 (duplicate associated constant B).

The input below compiles, and the earlier transform produced compiling output. Please include the deferred impls in type-equivalence decisions and deduplicate equivalent blocks when their self types merge. If the deferred impls differ, those differences also need to affect whether the self types can be unified.

Reproducer

Run c2rust-refactor reorganize_definitions --rewrite-mode alongside -- repro.rs --edition=2021 and compile the resulting repro.new.

#![feature(register_tool)]
#![register_tool(c2rust)]
#![allow(dead_code, non_camel_case_types)]

pub mod a {
    #[c2rust::header_src = "/tmp/types.h:1"]
    pub mod types_h {
        pub struct Thing { pub x: i32 }
        impl Thing { pub const A: i32 = 1; }
        impl Thing { pub const B: i32 = 2; }
    }
    pub fn go() -> i32 { types_h::Thing::A }
}
pub mod b {
    #[c2rust::header_src = "/tmp/types.h:1"]
    pub mod types_h {
        pub struct Thing { pub x: i32 }
        impl Thing { pub const A: i32 = 1; }
        impl Thing { pub const B: i32 = 2; }
    }
    pub fn go() -> i32 { types_h::Thing::A }
}
fn main() {}

[thedataking]

[P2] Rewrite the trait reference before moving a trait impl

canonicalize_moved_decl_paths uses fold_resolved_paths_with_id, which does not visit TraitRef paths. When an impl moves to its self type's module, its trait name can therefore remain relative to the old header scope.

In the input below, the trait moves to crate::user::MyTrait and the impl moves to defs, but the emitted impl still says impl MyTrait for crate::defs::Thing. The input compiles; the output fails with E0405 because MyTrait is not in scope in defs. Please rewrite the impl's trait reference, including any trait paths in bounds, as part of relocation.

This exercises the trait-impl support introduced here with edited Rust code.

Reproducer

Run c2rust-refactor reorganize_definitions --rewrite-mode alongside -- repro.rs --edition=2021 and compile the resulting repro.new.

#![feature(register_tool)]
#![register_tool(c2rust)]
#![allow(dead_code, non_camel_case_types)]

pub mod defs {
    pub struct Thing { pub x: i32 }
}
pub mod user {
    #[c2rust::header_src = "/tmp/user.h:1"]
    pub mod user_h {
        pub trait MyTrait { fn val(&self) -> i32; }
        impl MyTrait for crate::defs::Thing {
            fn val(&self) -> i32 { self.x }
        }
    }
    pub fn go() {}
}
fn main() {}