Upgrade to syn v3.0

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.68.0
+          - 1.71.0
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1
@@ -34,7 +34,7 @@ jobs:
       matrix:
         rust:
           - 1.79.0
-          # It's useful to test applications of these macros to newer features so using 1.68 for tests doesn't work
+          # It's useful to test applications of these macros to newer features so using 1.71 for tests doesn't work
           # This needs to be locked to a specific version of Rust since the exact error messages may change
           # When switching this Rust version make sure to also update tests to use newer error messages if applicable
     steps:

README.md

@@ -17,7 +17,7 @@ Delegating the implementation of traits to enum variants or fields of a struct n
 code. Ambassador is an attempt to eliminate that boilerplate by deriving the delegating trait implementation via
 procedural macros.
 
-**The minimum supported Rust version is 1.68.0.**
+**The minimum supported Rust version is 1.71.0.**
 
 ## Installation
 

ambassador/Cargo.toml

@@ -13,7 +13,7 @@ readme = "README.md"
 proc-macro = true
 
 [dependencies]
-syn = { version = "2", features = ["full", "extra-traits"] }
+syn = { version = "3", features = ["full", "extra-traits"] }
 quote = "1.0.2"
 proc-macro2 = "1.0.6"
 itertools = "0.10.3"

ambassador/src/register.rs

@@ -5,7 +5,7 @@ use proc_macro2::{Ident, TokenStream, TokenTree};
 use quote::{quote, ToTokens, TokenStreamExt};
 use syn::spanned::Spanned;
 use syn::{
-    AttrStyle, Attribute, ConstParam, GenericParam, ItemTrait, LifetimeParam, ReturnType,
+    AttrStyle, Attribute, ConstParam, GenericParam, ItemTrait, LifetimeParam, ReturnType, Safety,
     TraitItem, TraitItemConst, TraitItemType, TypeParam, Visibility,
 };
 
@@ -411,7 +411,7 @@ fn build_method_invocation(
     } else {
         quote! { $ret #field.#method_ident::<#(#generics,)*>(#argument_list) #post }
     };
-    if original_method.sig.unsafety.is_some() {
+    if matches!(original_method.sig.safety, Safety::Unsafe(_)) {
         method_invocation = quote! (
             // SAFETY: All safety obligation are passed along
             unsafe {#method_invocation}

ambassador/src/util.rs

@@ -3,7 +3,7 @@ use quote::ToTokens;
 use std::fmt::{Display, Formatter};
 use syn::punctuated::Punctuated;
 use syn::spanned::Spanned;
-use syn::{Receiver, Result};
+use syn::{ReceiverKind, Result, Token};
 
 macro_rules! error {
     ($span:expr, $($rest:expr),*) => {Err(syn::parse::Error::new($span, format_args!($($rest),*)))};
@@ -110,23 +110,20 @@ impl Display for ReceiverType {
     }
 }
 
-fn receiver_type_inner(r: &Receiver) -> ReceiverType {
-    if r.reference.is_none() {
-        ReceiverType::Owned
-    } else if r.mutability.is_none() {
-        ReceiverType::Ref
-    } else {
-        ReceiverType::MutRef
-    }
-}
-
 pub(crate) fn receiver_type(sig: &syn::Signature) -> Result<ReceiverType> {
-    match sig.receiver() {
-        Some(r) if r.colon_token.is_none() => Ok(receiver_type_inner(r)),
-        Some(r) => error!(
-            r.span(),
+    let Some(receiver) = sig.receiver() else {
+        return error!(sig.paren_token.span.open(), "method must have a receiver");
+    };
+    match receiver.kind {
+        ReceiverKind::Value => Ok(ReceiverType::Owned),
+        ReceiverKind::Reference(_, _, None) => Ok(ReceiverType::Ref),
+        ReceiverKind::Reference(_, _, Some(x)) => {
+            let _: Token![mut] = x;
+            Ok(ReceiverType::MutRef)
+        }
+        _ => error!(
+            receiver.span(),
             "method's receiver type is not supported (must one of self, &self, or &mut self)"
         ),
-        None => error!(sig.paren_token.span.open(), "method must have a receiver"),
     }
 }