By name: rust-macro-expand description: Use cargo-expand to inspect derive/proc-macro output before guessing at compiler errors that mention generated code.
rust-macro-expand
When a compiler error mentions a derive macro, attribute macro, or a
type that's clearly synthesized (e.g. <MyType as Serialize>::serialize
and the user didn't write a Serialize impl), expand the macro first:
cargo +nightly expand --package <crate> <path>
Common forms:
- Whole binary:
cargo +nightly expand --package <crate> --bin <bin> - Whole lib:
cargo +nightly expand --package <crate> --lib - One module:
cargo +nightly expand --package <crate> <module::path>
Pipe through | head -200 to keep the output context-friendly. If the
expansion is huge, look at the specific item with the --package /
module path narrowed.
Don't speculate about what #[derive(Foo)] generates — read it.