Fix thrust-macros build against syn 3.0

syn 3.0 restructures method receivers: Receiver::ty is replaced by a
ReceiverKind enum (Value/Reference/Typed), and Punctuated::pop() now
returns the element directly instead of a Pair, so Pair::into_value()
no longer applies.

Add a receiver_type() helper that reconstructs the effective self type
(mirroring syn 2's Receiver::ty) and use it at both call sites, and
drop the now-unnecessary into_value() calls in spec.rs.

Author: claude

thrust-macros/src/formula_fn_type_lowering.rs

@@ -49,7 +49,7 @@ impl<'a> FormulaFnTypeLowering<'a> {
         for arg in args {
             match arg {
                 syn::FnArg::Receiver(receiver) => {
-                    let ty = &receiver.ty;
+                    let ty = crate::receiver_type(receiver);
                     model_inputs.push(syn::parse_quote!(self_: <#ty as thrust_models::Model>::Ty));
                 }
                 syn::FnArg::Typed(pt) => {

thrust-macros/src/invariant.rs

@@ -300,7 +300,7 @@ impl VisitMut for SelfValueRewriter {
         match arg {
             syn::FnArg::Receiver(receiver) => {
                 let to = &self.to;
-                let ty = &receiver.ty;
+                let ty = crate::receiver_type(receiver);
                 *arg = syn::parse_quote!(#to: #ty);
             }
             syn::FnArg::Typed(_) => { /* handled by visit_pat_ident_mut */ }

thrust-macros/src/lib.rs

@@ -133,6 +133,26 @@ pub fn sig(attr: TokenStream, item: TokenStream) -> TokenStream {
     rty::expand_sig(attr, item)
 }
 
+/// Reconstructs the effective type of a method receiver (`&self` -> `&Self`,
+/// `&mut self` -> `&mut Self`, `self` -> `Self`, `self: T` -> `T`), mirroring
+/// what syn 2's `Receiver::ty` used to provide directly.
+fn receiver_type(receiver: &syn::Receiver) -> syn::Type {
+    match &receiver.kind {
+        syn::ReceiverKind::Typed(_, ty) => (**ty).clone(),
+        syn::ReceiverKind::Reference(and_token, lifetime, mutability) => {
+            syn::Type::Reference(syn::TypeReference {
+                attrs: Vec::new(),
+                and_token: *and_token,
+                lifetime: lifetime.clone(),
+                mutability: *mutability,
+                elem: Box::new(syn::parse_quote!(Self)),
+            })
+        }
+        syn::ReceiverKind::Value => syn::parse_quote!(Self),
+        _ => unimplemented!("unknown syn::ReceiverKind variant"),
+    }
+}
+
 fn tokens_contain_ident<T>(tokens: &TokenStream2, target: T) -> bool
 where
     T: AsRef<str>,

thrust-macros/src/spec.rs

@@ -99,8 +99,8 @@ pub fn expand_requires_ensures(attr: TokenStream, item: TokenStream) -> TokenStr
         .into();
     }
 
-    let ens_expr = exprs.pop().unwrap().into_value();
-    let req_expr = exprs.pop().unwrap().into_value();
+    let ens_expr = exprs.pop().unwrap();
+    let req_expr = exprs.pop().unwrap();
 
     let func = parse_macro_input!(item as FnItemWithSignature);
     let outer_context = match extract_outer_context(&func) {
@@ -225,8 +225,8 @@ fn extract_requires_ensures(func: &mut FnItemWithSignature) -> syn::Result<(syn:
                     "expected exactly two comma-separated expressions in _requires_ensures attribute",
                 ));
             }
-            let ens_expr = exprs.pop().unwrap().into_value();
-            let req_expr = exprs.pop().unwrap().into_value();
+            let ens_expr = exprs.pop().unwrap();
+            let req_expr = exprs.pop().unwrap();
             result = Some((req_expr, ens_expr));
         }
     }