Function expand_set_assertion

assert-struct-macros/src/expand.rs:754–800

Generate set assertion using backtracking to match patterns in any order. Each element pattern becomes a predicate closure that shadows `__report` with a probe report, allowing the existing assertion code to be reused unchanged. The runtime `set_match` function owns the length check and backtracking algorithm.

(value_expr: &TokenStream, pattern: &PatternSet)

/// probe report, allowing the existing assertion code to be reused unchanged. The
/// runtime `set_match` function owns the length check and backtracking algorithm.
fn expand_set_assertion(value_expr: &TokenStream, pattern: &PatternSet) -> TokenStream {
    let elements = &pattern.elements;
    let rest = pattern.rest;
    let node_ident = expand_pattern_node_ident(pattern.node_id);

    // Generate one named predicate binding per element pattern.
    // Each closure:
    //   1. Looks up the element by index from __set_coll (captured by ref)
    //   2. Shadows __report with a fresh probe report
    //   3. Runs the generated assertion (which writes to the local __report)
    //   4. Returns true iff no errors were pushed (i.e. the pattern matched)
    let pred_names: Vec<_> = (0..elements.len())
        .map(|i| quote::format_ident!("__set_pred_{}", i))
        .collect();

    let pred_defs: Vec<TokenStream> = elements
        .iter()
        .zip(pred_names.iter())
        .map(|(elem, name)| {
            let assertion = expand_pattern_assertion(&quote! { __set_elem }, elem);
            quote! {
                let #name = |__set_idx: usize| -> bool {
                    let __set_elem = __set_coll[__set_idx];
                    #[allow(unused_mut)]
                    let mut __report = ::assert_struct::__macro_support::ErrorReport::new_probe();
                    #assertion
                    __report.is_empty()
                };
            }
        })
        .collect();

    quote! {
        {
            let __set_coll: ::std::vec::Vec<_> = (&(#value_expr)).into_iter().collect();
            #(#pred_defs)*
            let __set_preds: &[&dyn ::std::ops::Fn(usize) -> bool] = &[#(&#pred_names),*];
            ::assert_struct::__macro_support::set_match(
                __set_coll.len(),
                #rest,
                __set_preds,
                &mut __report,
                &#node_ident,
            );
        }
    }
}

/// Generate the error context creation and push code
fn generate_error_push(