Use Item::expect_* and ImplItem::expect_* more

compiler/rustc_ast_lowering/src/item.rs

@@ -138,12 +138,10 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
             // Evaluate with the lifetimes in `params` in-scope.
             // This is used to track which lifetimes have already been defined,
             // and which need to be replicated when lowering an async fn.
-            match parent_hir.node().expect_item().kind {
-                hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
-                    lctx.is_in_trait_impl = of_trait.is_some();
-                }
-                _ => {}
-            };
+
+            if let hir::ItemKind::Impl(impl_) = parent_hir.node().expect_item().kind {
+                lctx.is_in_trait_impl = impl_.of_trait.is_some();
+            }
 
             match ctxt {
                 AssocCtxt::Trait => hir::OwnerNode::TraitItem(lctx.lower_trait_item(item)),

compiler/rustc_hir/src/hir.rs

@@ -3146,7 +3146,6 @@ impl<'hir> Item<'hir> {
         (ty, gen)
     }
 
-    /// An opaque `impl Trait` type alias, e.g., `type Foo = impl Bar;`.
     /// Expect an [`ItemKind::OpaqueTy`] or panic.
     #[track_caller]
     pub fn expect_opaque_ty(&self) -> &OpaqueTy<'hir> {
@@ -3168,7 +3167,6 @@ impl<'hir> Item<'hir> {
         (data, gen)
     }
 
-    /// A union definition, e.g., `union Foo<A, B> {x: A, y: B}`.
     /// Expect an [`ItemKind::Union`] or panic.
     #[track_caller]
     pub fn expect_union(&self) -> (&VariantData<'hir>, &'hir Generics<'hir>) {

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -74,10 +74,9 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
 
     debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type);
 
-    let span = match tcx.hir().expect_item(impl_did).kind {
-        ItemKind::Impl(hir::Impl { polarity: hir::ImplPolarity::Negative(_), .. }) => return,
-        ItemKind::Impl(impl_) => impl_.self_ty.span,
-        _ => bug!("expected Copy impl item"),
+    let span = match tcx.hir().expect_item(impl_did).expect_impl() {
+        hir::Impl { polarity: hir::ImplPolarity::Negative(_), .. } => return,
+        hir::Impl { self_ty, .. } => self_ty.span,
     };
 
     let cause = traits::ObligationCause::misc(span, impl_did);

compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs

@@ -462,10 +462,7 @@ fn foo(&self) -> Self::T { String::new() }
         if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = *proj_ty.self_ty().kind() {
             let opaque_local_def_id = def_id.as_local();
             let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id {
-                match &tcx.hir().expect_item(opaque_local_def_id).kind {
-                    hir::ItemKind::OpaqueTy(opaque_hir_ty) => opaque_hir_ty,
-                    _ => bug!("The HirId comes from a `ty::Opaque`"),
-                }
+                tcx.hir().expect_item(opaque_local_def_id).expect_opaque_ty()
             } else {
                 return false;
             };

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -392,12 +392,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// defining scope.
     #[instrument(skip(self), level = "trace", ret)]
     fn opaque_type_origin_unchecked(&self, def_id: LocalDefId) -> OpaqueTyOrigin {
-        match self.tcx.hir().expect_item(def_id).kind {
-            hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => origin,
-            ref itemkind => {
-                bug!("weird opaque type: {:?}, {:#?}", def_id, itemkind)
-            }
-        }
+        self.tcx.hir().expect_item(def_id).expect_opaque_ty().origin
     }
 }
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1469,8 +1469,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
 
         match impl_item.kind {
             ty::AssocKind::Fn => {
-                let ast_item = self.tcx.hir().expect_impl_item(def_id.expect_local());
-                let hir::ImplItemKind::Fn(ref sig, body) = ast_item.kind else { bug!() };
+                let (sig, body) =
+                    self.tcx.hir().expect_impl_item(def_id.expect_local()).expect_fn();
                 self.tables.asyncness.set_some(def_id.index, sig.header.asyncness);
                 record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
                 // Can be inside `impl const Trait`, so using sig.header.constness is not reliable