Update the syn crate and adopt let_else in three more places

The syn crate has gained support for let_else syntax in version 1.0.76,
see dtolnay/syn#1057 .

In the three instances that use let_else, we've sent code through an
attr macro, which would create compile errors when there was no
let_else support in syn. To avoid this, we ran
`cargo +nightly update -p syn` for updating the syn crate.

Cargo.lock

@@ -2728,9 +2728,9 @@ checksum = "bc881b2c22681370c6a780e47af9840ef841837bc98118431d4e1868bd0c1086"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.24"
+version = "1.0.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+checksum = "edc3358ebc67bc8b7fa0c007f945b0b18226f78437d61bec735a9eb96b61ee70"
 dependencies = [
  "unicode-xid",
 ]
@@ -5090,9 +5090,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "1.0.65"
+version = "1.0.80"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f3a1d708c221c5a612956ef9f75b37e454e88d1f7b899fbd3a18d4252012d663"
+checksum = "d010a1623fbd906d51d650a9916aaefc05ffa0e4053ff7fe601167f3e715d194"
 dependencies = [
  "proc-macro2",
  "quote",

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1057,9 +1057,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                     match param.kind {
                         GenericParamKind::Lifetime { .. } => {
                             let (name, reg) = Region::early(&self.tcx.hir(), &mut index, &param);
-                            let def_id = if let Region::EarlyBound(_, def_id, _) = reg {
-                                def_id
-                            } else {
+                            let Region::EarlyBound(_, def_id, _) = reg else {
                                 bug!();
                             };
                             // We cannot predict what lifetimes are unused in opaque type.

compiler/rustc_typeck/src/check/coercion.rs

@@ -521,9 +521,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         let traits =
             (self.tcx.lang_items().unsize_trait(), self.tcx.lang_items().coerce_unsized_trait());
-        let (unsize_did, coerce_unsized_did) = if let (Some(u), Some(cu)) = traits {
-            (u, cu)
-        } else {
+        let (Some(unsize_did), Some(coerce_unsized_did)) = traits else {
             debug!("missing Unsize or CoerceUnsized traits");
             return Err(TypeError::Mismatch);
         };

compiler/rustc_typeck/src/check/upvar.rs

@@ -1678,9 +1678,7 @@ impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
         diag_expr_id: hir::HirId,
     ) {
         let tcx = self.fcx.tcx;
-        let upvar_id = if let PlaceBase::Upvar(upvar_id) = place_with_id.place.base {
-            upvar_id
-        } else {
+        let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else {
             return;
         };