Rollup merge of #141741 - nnethercote:overhaul-UsePath, r=petrochenkov

Overhaul `UsePath`

It currently uses `SmallVec<[Res; 3]>` which is really weird. Details in the individual commits.

r? `@petrochenkov`

2 files changed, 20 insertions, 21 deletions

diff --git a/compiler/rustc_lint/src/internal.rs b/compiler/rustc_lint/src/internal.rs
index 1d4be24ea9f..1805a674d68 100644
--- a/compiler/rustc_lint/src/internal.rs
+++ b/compiler/rustc_lint/src/internal.rs
@@ -328,16 +328,19 @@ impl<'tcx> LateLintPass<'tcx> for TypeIr {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
         let rustc_hir::ItemKind::Use(path, kind) = item.kind else { return };
 
-        let is_mod_inherent = |def_id| cx.tcx.is_diagnostic_item(sym::type_ir_inherent, def_id);
+        let is_mod_inherent = |res: Res| {
+            res.opt_def_id()
+                .is_some_and(|def_id| cx.tcx.is_diagnostic_item(sym::type_ir_inherent, def_id))
+        };
 
         // Path segments except for the final.
-        if let Some(seg) =
-            path.segments.iter().find(|seg| seg.res.opt_def_id().is_some_and(is_mod_inherent))
-        {
+        if let Some(seg) = path.segments.iter().find(|seg| is_mod_inherent(seg.res)) {
             cx.emit_span_lint(USAGE_OF_TYPE_IR_INHERENT, seg.ident.span, TypeIrInherentUsage);
         }
         // Final path resolutions, like `use rustc_type_ir::inherent`
-        else if path.res.iter().any(|res| res.opt_def_id().is_some_and(is_mod_inherent)) {
+        else if let Some(type_ns) = path.res.type_ns
+            && is_mod_inherent(type_ns)
+        {
             cx.emit_span_lint(
                 USAGE_OF_TYPE_IR_INHERENT,
                 path.segments.last().unwrap().ident.span,
@@ -346,13 +349,12 @@ impl<'tcx> LateLintPass<'tcx> for TypeIr {
         }
 
         let (lo, hi, snippet) = match path.segments {
-            [.., penultimate, segment]
-                if penultimate.res.opt_def_id().is_some_and(is_mod_inherent) =>
-            {
+            [.., penultimate, segment] if is_mod_inherent(penultimate.res) => {
                 (segment.ident.span, item.kind.ident().unwrap().span, "*")
             }
             [.., segment]
-                if path.res.iter().flat_map(Res::opt_def_id).any(is_mod_inherent)
+                if let Some(type_ns) = path.res.type_ns
+                    && is_mod_inherent(type_ns)
                     && let rustc_hir::UseKind::Single(ident) = kind =>
             {
                 let (lo, snippet) =
diff --git a/compiler/rustc_lint/src/unqualified_local_imports.rs b/compiler/rustc_lint/src/unqualified_local_imports.rs
index 50c5119285f..0076cae3cff 100644
--- a/compiler/rustc_lint/src/unqualified_local_imports.rs
+++ b/compiler/rustc_lint/src/unqualified_local_imports.rs
@@ -1,4 +1,3 @@
-use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{self as hir};
 use rustc_session::{declare_lint, declare_lint_pass};
 use rustc_span::kw;
@@ -47,17 +46,15 @@ declare_lint_pass!(UnqualifiedLocalImports => [UNQUALIFIED_LOCAL_IMPORTS]);
 impl<'tcx> LateLintPass<'tcx> for UnqualifiedLocalImports {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
         let hir::ItemKind::Use(path, _kind) = item.kind else { return };
-        // `path` has three resolutions for the type, module, value namespaces.
-        // Check if any of them qualifies: local crate, and not a macro.
-        // (Macros can't be imported any other way so we don't complain about them.)
-        let is_local_import = |res: &Res| {
-            matches!(
-                res,
-                hir::def::Res::Def(def_kind, def_id)
-                    if def_id.is_local() && !matches!(def_kind, DefKind::Macro(_)),
-            )
-        };
-        if !path.res.iter().any(is_local_import) {
+        // Check the type and value namespace resolutions for a local crate.
+        let is_local_import = matches!(
+            path.res.type_ns,
+            Some(hir::def::Res::Def(_, def_id)) if def_id.is_local()
+        ) || matches!(
+            path.res.value_ns,
+            Some(hir::def::Res::Def(_, def_id)) if def_id.is_local()
+        );
+        if !is_local_import {
             return;
         }
         // So this does refer to something local. Let's check whether it starts with `self`,