Remove useless smallvec dependency in rustc_lint::non_local_def

Cargo.lock

@@ -4133,7 +4133,6 @@ dependencies = [
  "rustc_target",
  "rustc_trait_selection",
  "rustc_type_ir",
- "smallvec",
  "tracing",
  "unicode-security",
 ]

compiler/rustc_lint/Cargo.toml

@@ -23,7 +23,6 @@ rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_type_ir = { path = "../rustc_type_ir" }
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 tracing = "0.1"
 unicode-security = "0.1.0"
 # tidy-alphabetical-end

compiler/rustc_lint/src/non_local_def.rs

@@ -2,8 +2,6 @@
 use rustc_span::def_id::{DefId, LOCAL_CRATE};
 use rustc_span::{sym, symbol::kw, ExpnKind, MacroKind};
 
-use smallvec::{smallvec, SmallVec};
-
 use crate::lints::{NonLocalDefinitionsCargoUpdateNote, NonLocalDefinitionsDiag};
 use crate::{LateContext, LateLintPass, LintContext};
 
@@ -114,25 +112,25 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
                 // is using local items and so we don't lint on it.
 
                 // We also ignore anon-const in item by including the anon-const
-                // parent as well; and since it's quite uncommon, we use smallvec
-                // to avoid unnecessary heap allocations.
-                let local_parents: SmallVec<[DefId; 1]> = if parent_def_kind == DefKind::Const
+                // parent as well.
+                let parent_parent = if parent_def_kind == DefKind::Const
                     && parent_opt_item_name == Some(kw::Underscore)
                 {
-                    smallvec![parent, cx.tcx.parent(parent)]
+                    Some(cx.tcx.parent(parent))
                 } else {
-                    smallvec![parent]
+                    None
                 };
 
                 let self_ty_has_local_parent = match impl_.self_ty.kind {
                     TyKind::Path(QPath::Resolved(_, ty_path)) => {
-                        path_has_local_parent(ty_path, cx, &*local_parents)
+                        path_has_local_parent(ty_path, cx, parent, parent_parent)
                     }
                     TyKind::TraitObject([principle_poly_trait_ref, ..], _, _) => {
                         path_has_local_parent(
                             principle_poly_trait_ref.trait_ref.path,
                             cx,
-                            &*local_parents,
+                            parent,
+                            parent_parent,
                         )
                     }
                     TyKind::TraitObject([], _, _)
@@ -154,7 +152,7 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
 
                 let of_trait_has_local_parent = impl_
                     .of_trait
-                    .map(|of_trait| path_has_local_parent(of_trait.path, cx, &*local_parents))
+                    .map(|of_trait| path_has_local_parent(of_trait.path, cx, parent, parent_parent))
                     .unwrap_or(false);
 
                 // If none of them have a local parent (LOGICAL NOR) this means that
@@ -218,6 +216,14 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
 ///    std::convert::PartialEq<Foo<Bar>>
 ///    ^^^^^^^^^^^^^^^^^^^^^^^
 /// ```
-fn path_has_local_parent(path: &Path<'_>, cx: &LateContext<'_>, local_parents: &[DefId]) -> bool {
-    path.res.opt_def_id().is_some_and(|did| local_parents.contains(&cx.tcx.parent(did)))
+fn path_has_local_parent(
+    path: &Path<'_>,
+    cx: &LateContext<'_>,
+    impl_parent: DefId,
+    impl_parent_parent: Option<DefId>,
+) -> bool {
+    path.res.opt_def_id().is_some_and(|did| {
+        let res_parent = cx.tcx.parent(did);
+        res_parent == impl_parent || Some(res_parent) == impl_parent_parent
+    })
 }