Use hir::Node helper methods instead of repeat the same impl multiple times

There already were inconsistencies, so this ensures we don't introduce subtle surprising bugs

Author: oli-obk

Diff for: compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -508,29 +508,9 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
         visitor.has_late_bound_regions
     }
 
-    match node {
-        Node::TraitItem(item) => match &item.kind {
-            hir::TraitItemKind::Fn(sig, _) => has_late_bound_regions(tcx, item.generics, sig.decl),
-            _ => None,
-        },
-        Node::ImplItem(item) => match &item.kind {
-            hir::ImplItemKind::Fn(sig, _) => has_late_bound_regions(tcx, item.generics, sig.decl),
-            _ => None,
-        },
-        Node::ForeignItem(item) => match item.kind {
-            hir::ForeignItemKind::Fn(fn_decl, _, generics) => {
-                has_late_bound_regions(tcx, generics, fn_decl)
-            }
-            _ => None,
-        },
-        Node::Item(item) => match &item.kind {
-            hir::ItemKind::Fn(sig, .., generics, _) => {
-                has_late_bound_regions(tcx, generics, sig.decl)
-            }
-            _ => None,
-        },
-        _ => None,
-    }
+    let decl = node.fn_decl()?;
+    let generics = node.generics()?;
+    has_late_bound_regions(tcx, generics, decl)
 }
 
 struct AnonConstInParamTyDetector {

Diff for: compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -123,43 +123,22 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     // Preserving the order of insertion is important here so as not to break UI tests.
     let mut predicates: FxIndexSet<(ty::Clause<'_>, Span)> = FxIndexSet::default();
 
-    let ast_generics = match node {
-        Node::TraitItem(item) => item.generics,
-
-        Node::ImplItem(item) => item.generics,
-
-        Node::Item(item) => match item.kind {
+    let ast_generics = node.generics().unwrap_or(NO_GENERICS);
+    if let Node::Item(item) = node {
+        match item.kind {
             ItemKind::Impl(impl_) => {
                 if impl_.defaultness.is_default() {
                     is_default_impl_trait = tcx
                         .impl_trait_ref(def_id)
                         .map(|t| ty::Binder::dummy(t.instantiate_identity()));
                 }
-                impl_.generics
             }
-            ItemKind::Fn(.., generics, _)
-            | ItemKind::TyAlias(_, generics)
-            | ItemKind::Const(_, generics, _)
-            | ItemKind::Enum(_, generics)
-            | ItemKind::Struct(_, generics)
-            | ItemKind::Union(_, generics) => generics,
-
-            ItemKind::Trait(_, _, generics, self_bounds, ..)
-            | ItemKind::TraitAlias(generics, self_bounds) => {
+
+            ItemKind::Trait(_, _, _, self_bounds, ..) | ItemKind::TraitAlias(_, self_bounds) => {
                 is_trait = Some(self_bounds);
-                generics
             }
-            ItemKind::OpaqueTy(OpaqueTy { generics, .. }) => generics,
-            _ => NO_GENERICS,
-        },
-
-        Node::ForeignItem(item) => match item.kind {
-            ForeignItemKind::Static(..) => NO_GENERICS,
-            ForeignItemKind::Fn(_, _, generics) => generics,
-            ForeignItemKind::Type => NO_GENERICS,
-        },
-
-        _ => NO_GENERICS,
+            _ => {}
+        }
     };
 
     let generics = tcx.generics_of(def_id);
@@ -703,45 +682,17 @@ pub(super) fn type_param_predicates(
     let mut extend = None;
 
     let item_hir_id = tcx.local_def_id_to_hir_id(item_def_id);
-    let ast_generics = match tcx.hir_node(item_hir_id) {
-        Node::TraitItem(item) => item.generics,
-
-        Node::ImplItem(item) => item.generics,
-
-        Node::Item(item) => {
-            match item.kind {
-                ItemKind::Fn(.., generics, _)
-                | ItemKind::Impl(&hir::Impl { generics, .. })
-                | ItemKind::TyAlias(_, generics)
-                | ItemKind::Const(_, generics, _)
-                | ItemKind::OpaqueTy(&OpaqueTy {
-                    generics,
-                    origin: hir::OpaqueTyOrigin::TyAlias { .. },
-                    ..
-                })
-                | ItemKind::Enum(_, generics)
-                | ItemKind::Struct(_, generics)
-                | ItemKind::Union(_, generics) => generics,
-                ItemKind::Trait(_, _, generics, ..) => {
-                    // Implied `Self: Trait` and supertrait bounds.
-                    if param_id == item_hir_id {
-                        let identity_trait_ref =
-                            ty::TraitRef::identity(tcx, item_def_id.to_def_id());
-                        extend = Some((identity_trait_ref.to_predicate(tcx), item.span));
-                    }
-                    generics
-                }
-                _ => return result,
-            }
-        }
-
-        Node::ForeignItem(item) => match item.kind {
-            ForeignItemKind::Fn(_, _, generics) => generics,
-            _ => return result,
-        },
 
-        _ => return result,
-    };
+    let hir_node = tcx.hir_node(item_hir_id);
+    let Some(ast_generics) = hir_node.generics() else { return result };
+    if let Node::Item(item) = hir_node
+        && let ItemKind::Trait(..) = item.kind
+        // Implied `Self: Trait` and supertrait bounds.
+        && param_id == item_hir_id
+    {
+        let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id.to_def_id());
+        extend = Some((identity_trait_ref.to_predicate(tcx), item.span));
+    }
 
     let icx = ItemCtxt::new(tcx, item_def_id);
     let extra_predicates = extend.into_iter().chain(

Diff for: compiler/rustc_hir_typeck/src/lib.rs

@@ -95,29 +95,7 @@ macro_rules! type_error_struct {
 fn primary_body_of(
     node: Node<'_>,
 ) -> Option<(hir::BodyId, Option<&hir::Ty<'_>>, Option<&hir::FnSig<'_>>)> {
-    match node {
-        Node::Item(item) => match item.kind {
-            hir::ItemKind::Const(ty, _, body) | hir::ItemKind::Static(ty, _, body) => {
-                Some((body, Some(ty), None))
-            }
-            hir::ItemKind::Fn(ref sig, .., body) => Some((body, None, Some(sig))),
-            _ => None,
-        },
-        Node::TraitItem(item) => match item.kind {
-            hir::TraitItemKind::Const(ty, Some(body)) => Some((body, Some(ty), None)),
-            hir::TraitItemKind::Fn(ref sig, hir::TraitFn::Provided(body)) => {
-                Some((body, None, Some(sig)))
-            }
-            _ => None,
-        },
-        Node::ImplItem(item) => match item.kind {
-            hir::ImplItemKind::Const(ty, body) => Some((body, Some(ty), None)),
-            hir::ImplItemKind::Fn(ref sig, body) => Some((body, None, Some(sig))),
-            _ => None,
-        },
-        Node::AnonConst(constant) => Some((constant.body, None, None)),
-        _ => None,
-    }
+    Some((node.body_id()?, node.ty(), node.fn_sig()))
 }
 
 fn has_typeck_results(tcx: TyCtxt<'_>, def_id: DefId) -> bool {

Diff for: compiler/rustc_passes/src/check_attr.rs

@@ -609,13 +609,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     && !self.tcx.sess.target.is_like_wasm
                     && !self.tcx.sess.opts.actually_rustdoc
                 {
-                    let hir::Node::Item(item) = self.tcx.hir_node(hir_id) else {
-                        unreachable!();
-                    };
-                    let hir::ItemKind::Fn(sig, _, _) = item.kind else {
-                        // target is `Fn`
-                        unreachable!();
-                    };
+                    let sig = self.tcx.hir_node(hir_id).fn_sig().unwrap();
 
                     self.dcx().emit_err(errors::LangItemWithTargetFeature {
                         attr_span: attr.span,