Macro batch_preprocess_test 

batch_preprocess_test!() { /* proc-macro */ }

Reference open-extension macro — the reference implementation of the open-extension protocol (also the test consumer) (function-like): name!{ {spec}(method name list){body} trait T {...} }.

Parses the spec body (first Brace group — the target type), the method name list, the body, and the trait definition from the macro input. In the top-level form (4 segments) it emits a full impl Trait for {spec}; in the legacy in-impl form (3 segments, no spec group) it emits fn signature { body } per method (reusing the trait signature) — equivalent to handing the #fill implementation to the user.

Used to verify open instruction extension: #name(args){body} expands to { ! name!{(args){body} trait ...} }, the ! marking top-level emission — codegen prepends the spec body and emits the call at top level, where the user macro generates arbitrary items (typically its own impl) (see section 28 of tests/dsl.rs).

Design point: this must be a function-like macro call name!{...}, not an #[name[...]] trait ... attribute — a trait is not a valid item inside an impl block (#[attr] trait cannot appear in an impl), whereas a function-like macro in an impl body position is expanded by rustc into associated items.