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`

Author: matthiaskrgr

compiler/rustc_ast_lowering/src/item.rs

@@ -3,10 +3,11 @@ use rustc_ast::ptr::P;
 use rustc_ast::visit::AssocCtxt;
 use rustc_ast::*;
 use rustc_errors::ErrorGuaranteed;
-use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def::{DefKind, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LocalDefId};
 use rustc_hir::{self as hir, HirId, LifetimeSource, PredicateOrigin};
 use rustc_index::{IndexSlice, IndexVec};
+use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::{DUMMY_SP, DesugaringKind, Ident, Span, Symbol, kw, sym};
@@ -527,7 +528,22 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
             UseTreeKind::Glob => {
                 let res = self.expect_full_res(id);
-                let res = smallvec![self.lower_res(res)];
+                let res = self.lower_res(res);
+                // Put the result in the appropriate namespace.
+                let res = match res {
+                    Res::Def(DefKind::Mod | DefKind::Trait, _) => {
+                        PerNS { type_ns: Some(res), value_ns: None, macro_ns: None }
+                    }
+                    Res::Def(DefKind::Enum, _) => {
+                        PerNS { type_ns: None, value_ns: Some(res), macro_ns: None }
+                    }
+                    Res::Err => {
+                        // Propagate the error to all namespaces, just to be sure.
+                        let err = Some(Res::Err);
+                        PerNS { type_ns: err, value_ns: err, macro_ns: err }
+                    }
+                    _ => span_bug!(path.span, "bad glob res {:?}", res),
+                };
                 let path = Path { segments, span: path.span, tokens: None };
                 let path = self.lower_use_path(res, &path, ParamMode::Explicit);
                 hir::ItemKind::Use(path, hir::UseKind::Glob)
@@ -601,7 +617,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 } else {
                     // For non-empty lists we can just drop all the data, the prefix is already
                     // present in HIR as a part of nested imports.
-                    self.arena.alloc(hir::UsePath { res: smallvec![], segments: &[], span })
+                    self.arena.alloc(hir::UsePath { res: PerNS::default(), segments: &[], span })
                 };
                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
             }

compiler/rustc_ast_lowering/src/lib.rs

@@ -64,7 +64,7 @@ use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_session::parse::{add_feature_diagnostics, feature_err};
 use rustc_span::symbol::{Ident, Symbol, kw, sym};
 use rustc_span::{DUMMY_SP, DesugaringKind, Span};
-use smallvec::{SmallVec, smallvec};
+use smallvec::SmallVec;
 use thin_vec::ThinVec;
 use tracing::{debug, instrument, trace};
 
@@ -705,14 +705,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.resolver.get_partial_res(id).map_or(Res::Err, |pr| pr.expect_full_res())
     }
 
-    fn lower_import_res(&mut self, id: NodeId, span: Span) -> SmallVec<[Res; 3]> {
-        let res = self.resolver.get_import_res(id).present_items();
-        let res: SmallVec<_> = res.map(|res| self.lower_res(res)).collect();
-        if res.is_empty() {
+    fn lower_import_res(&mut self, id: NodeId, span: Span) -> PerNS<Option<Res>> {
+        let per_ns = self.resolver.get_import_res(id);
+        let per_ns = per_ns.map(|res| res.map(|res| self.lower_res(res)));
+        if per_ns.is_empty() {
+            // Propagate the error to all namespaces, just to be sure.
             self.dcx().span_delayed_bug(span, "no resolution for an import");
-            return smallvec![Res::Err];
+            let err = Some(Res::Err);
+            return PerNS { type_ns: err, value_ns: err, macro_ns: err };
         }
-        res
+        per_ns
     }
 
     fn make_lang_item_qpath(

compiler/rustc_ast_lowering/src/path.rs

@@ -1,13 +1,13 @@
 use std::sync::Arc;
 
 use rustc_ast::{self as ast, *};
-use rustc_hir::def::{DefKind, PartialRes, Res};
+use rustc_hir::def::{DefKind, PartialRes, PerNS, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, GenericArg};
 use rustc_middle::{span_bug, ty};
 use rustc_session::parse::add_feature_diagnostics;
 use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Ident, Span, Symbol, sym};
-use smallvec::{SmallVec, smallvec};
+use smallvec::smallvec;
 use tracing::{debug, instrument};
 
 use super::errors::{
@@ -226,11 +226,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     pub(crate) fn lower_use_path(
         &mut self,
-        res: SmallVec<[Res; 3]>,
+        res: PerNS<Option<Res>>,
         p: &Path,
         param_mode: ParamMode,
     ) -> &'hir hir::UsePath<'hir> {
-        assert!((1..=3).contains(&res.len()));
+        assert!(!res.is_empty());
         self.arena.alloc(hir::UsePath {
             res,
             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {

compiler/rustc_hir/src/arena.rs

@@ -8,7 +8,6 @@ macro_rules! arena_types {
             [] asm_template: rustc_ast::InlineAsmTemplatePiece,
             [] attribute: rustc_hir::Attribute,
             [] owner_info: rustc_hir::OwnerInfo<'tcx>,
-            [] use_path: rustc_hir::UsePath<'tcx>,
             [] lit: rustc_hir::Lit,
             [] macro_def: rustc_ast::MacroDef,
         ]);

compiler/rustc_hir/src/def.rs

@@ -584,7 +584,7 @@ impl<CTX: crate::HashStableContext> ToStableHashKey<CTX> for Namespace {
 }
 
 /// Just a helper ‒ separate structure for each namespace.
-#[derive(Copy, Clone, Default, Debug)]
+#[derive(Copy, Clone, Default, Debug, HashStable_Generic)]
 pub struct PerNS<T> {
     pub value_ns: T,
     pub type_ns: T,
@@ -596,10 +596,16 @@ impl<T> PerNS<T> {
         PerNS { value_ns: f(self.value_ns), type_ns: f(self.type_ns), macro_ns: f(self.macro_ns) }
     }
 
+    /// Note: Do you really want to use this? Often you know which namespace a
+    /// name will belong in, and you can consider just that namespace directly,
+    /// rather than iterating through all of them.
     pub fn into_iter(self) -> IntoIter<T, 3> {
         [self.value_ns, self.type_ns, self.macro_ns].into_iter()
     }
 
+    /// Note: Do you really want to use this? Often you know which namespace a
+    /// name will belong in, and you can consider just that namespace directly,
+    /// rather than iterating through all of them.
     pub fn iter(&self) -> IntoIter<&T, 3> {
         [&self.value_ns, &self.type_ns, &self.macro_ns].into_iter()
     }
@@ -634,6 +640,10 @@ impl<T> PerNS<Option<T>> {
     }
 
     /// Returns an iterator over the items which are `Some`.
+    ///
+    /// Note: Do you really want to use this? Often you know which namespace a
+    /// name will belong in, and you can consider just that namespace directly,
+    /// rather than iterating through all of them.
     pub fn present_items(self) -> impl Iterator<Item = T> {
         [self.type_ns, self.value_ns, self.macro_ns].into_iter().flatten()
     }

compiler/rustc_hir/src/hir.rs

@@ -30,7 +30,7 @@ use thin_vec::ThinVec;
 use tracing::debug;
 
 use crate::LangItem;
-use crate::def::{CtorKind, DefKind, Res};
+use crate::def::{CtorKind, DefKind, PerNS, Res};
 use crate::def_id::{DefId, LocalDefIdMap};
 pub(crate) use crate::hir_id::{HirId, ItemLocalId, ItemLocalMap, OwnerId};
 use crate::intravisit::{FnKind, VisitorExt};
@@ -347,7 +347,7 @@ pub struct Path<'hir, R = Res> {
 }
 
 /// Up to three resolutions for type, value and macro namespaces.
-pub type UsePath<'hir> = Path<'hir, SmallVec<[Res; 3]>>;
+pub type UsePath<'hir> = Path<'hir, PerNS<Option<Res>>>;
 
 impl Path<'_> {
     pub fn is_global(&self) -> bool {

compiler/rustc_hir/src/intravisit.rs

@@ -1148,7 +1148,7 @@ pub fn walk_use<'v, V: Visitor<'v>>(
     hir_id: HirId,
 ) -> V::Result {
     let UsePath { segments, ref res, span } = *path;
-    for &res in res {
+    for res in res.present_items() {
         try_visit!(visitor.visit_path(&Path { segments, res, span }, hir_id));
     }
     V::Result::output()

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) =

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`,

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -1047,26 +1047,21 @@ fn find_fallback_pattern_typo<'tcx>(
                 let hir::ItemKind::Use(path, _) = item.kind else {
                     continue;
                 };
-                for res in &path.res {
-                    if let Res::Def(DefKind::Const, id) = res
-                        && infcx.can_eq(param_env, ty, cx.tcx.type_of(id).instantiate_identity())
-                    {
-                        if cx.tcx.visibility(id).is_accessible_from(parent, cx.tcx) {
-                            // The original const is accessible, suggest using it directly.
-                            let item_name = cx.tcx.item_name(*id);
-                            accessible.push(item_name);
-                            accessible_path.push(with_no_trimmed_paths!(cx.tcx.def_path_str(id)));
-                        } else if cx
-                            .tcx
-                            .visibility(item.owner_id)
-                            .is_accessible_from(parent, cx.tcx)
-                        {
-                            // The const is accessible only through the re-export, point at
-                            // the `use`.
-                            let ident = item.kind.ident().unwrap();
-                            imported.push(ident.name);
-                            imported_spans.push(ident.span);
-                        }
+                if let Some(value_ns) = path.res.value_ns
+                    && let Res::Def(DefKind::Const, id) = value_ns
+                    && infcx.can_eq(param_env, ty, cx.tcx.type_of(id).instantiate_identity())
+                {
+                    if cx.tcx.visibility(id).is_accessible_from(parent, cx.tcx) {
+                        // The original const is accessible, suggest using it directly.
+                        let item_name = cx.tcx.item_name(id);
+                        accessible.push(item_name);
+                        accessible_path.push(with_no_trimmed_paths!(cx.tcx.def_path_str(id)));
+                    } else if cx.tcx.visibility(item.owner_id).is_accessible_from(parent, cx.tcx) {
+                        // The const is accessible only through the re-export, point at
+                        // the `use`.
+                        let ident = item.kind.ident().unwrap();
+                        imported.push(ident.name);
+                        imported_spans.push(ident.span);
                     }
                 }
             }

compiler/rustc_passes/src/check_export.rs

@@ -132,7 +132,7 @@ impl<'tcx> Visitor<'tcx> for ExportableItemCollector<'tcx> {
                 self.add_exportable(def_id);
             }
             hir::ItemKind::Use(path, _) => {
-                for res in &path.res {
+                for res in path.res.present_items() {
                     // Only local items are exportable.
                     if let Some(res_id) = res.opt_def_id()
                         && let Some(res_id) = res_id.as_local()

compiler/rustc_resolve/src/check_unused.rs

@@ -118,9 +118,10 @@ impl<'a, 'ra, 'tcx> UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
             ast::UseTreeKind::Simple(Some(ident)) => {
                 if ident.name == kw::Underscore
                     && !self.r.import_res_map.get(&id).is_some_and(|per_ns| {
-                        per_ns.iter().filter_map(|res| res.as_ref()).any(|res| {
-                            matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
-                        })
+                        matches!(
+                            per_ns.type_ns,
+                            Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
+                        )
                     })
                 {
                     self.unused_import(self.base_id).add(id);

src/librustdoc/clean/mod.rs

@@ -1606,7 +1606,7 @@ fn first_non_private<'tcx>(
                     && let hir::Node::Item(item) = cx.tcx.hir_node_by_def_id(local_use_def_id)
                     && let hir::ItemKind::Use(path, hir::UseKind::Single(_)) = item.kind
                 {
-                    for res in &path.res {
+                    for res in path.res.present_items() {
                         if let Res::Def(DefKind::Ctor(..), _) | Res::SelfCtor(..) = res {
                             continue;
                         }
@@ -3014,7 +3014,7 @@ fn clean_use_statement<'tcx>(
 ) -> Vec<Item> {
     let mut items = Vec::new();
     let hir::UsePath { segments, ref res, span } = *path;
-    for &res in res {
+    for res in res.present_items() {
         let path = hir::Path { segments, res, span };
         items.append(&mut clean_use_statement_inner(import, name, &path, kind, cx, inlined_names));
     }

src/librustdoc/visit_ast.rs

@@ -440,7 +440,7 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
             hir::ItemKind::GlobalAsm { .. } => {}
             hir::ItemKind::Use(_, hir::UseKind::ListStem) => {}
             hir::ItemKind::Use(path, kind) => {
-                for &res in &path.res {
+                for res in path.res.present_items() {
                     // Struct and variant constructors and proc macro stubs always show up alongside
                     // their definitions, we've already processed them so just discard these.
                     if should_ignore_res(res) {

src/tools/clippy/clippy_lints/src/disallowed_types.rs

@@ -106,8 +106,8 @@ impl_lint_pass!(DisallowedTypes => [DISALLOWED_TYPES]);
 impl<'tcx> LateLintPass<'tcx> for DisallowedTypes {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
         if let ItemKind::Use(path, UseKind::Single(_)) = &item.kind {
-            for res in &path.res {
-                self.check_res_emit(cx, res, item.span);
+            if let Some(res) = path.res.type_ns {
+                self.check_res_emit(cx, &res, item.span);
             }
         }
     }

src/tools/clippy/clippy_lints/src/legacy_numeric_constants.rs

@@ -51,7 +51,9 @@ impl<'tcx> LateLintPass<'tcx> for LegacyNumericConstants {
         // so lint on the `use` statement directly.
         if let ItemKind::Use(path, kind @ (UseKind::Single(_) | UseKind::Glob)) = item.kind
             && !item.span.in_external_macro(cx.sess().source_map())
-            && let Some(def_id) = path.res[0].opt_def_id()
+            // use `present_items` because it could be in either type_ns or value_ns
+            && let Some(res) = path.res.present_items().next()
+            && let Some(def_id) = res.opt_def_id()
             && self.msrv.meets(cx, msrvs::NUMERIC_ASSOCIATED_CONSTANTS)
         {
             let module = if is_integer_module(cx, def_id) {

src/tools/clippy/clippy_lints/src/macro_use.rs

@@ -100,10 +100,7 @@ impl LateLintPass<'_> for MacroUseImports {
             && let hir_id = item.hir_id()
             && let attrs = cx.tcx.hir_attrs(hir_id)
             && let Some(mac_attr) = attrs.iter().find(|attr| attr.has_name(sym::macro_use))
-            && let Some(id) = path.res.iter().find_map(|res| match res {
-                Res::Def(DefKind::Mod, id) => Some(id),
-                _ => None,
-            })
+            && let Some(Res::Def(DefKind::Mod, id)) = path.res.type_ns
             && !id.is_local()
         {
             for kid in cx.tcx.module_children(id) {

src/tools/clippy/clippy_lints/src/min_ident_chars.rs

@@ -131,8 +131,9 @@ impl Visitor<'_> for IdentVisitor<'_, '_> {
             // If however the identifier is different, this means it is an alias (`use foo::bar as baz`). In
             // this case, we need to emit the warning for `baz`.
             if let Some(imported_item_path) = usenode
-                && let Some(Res::Def(_, imported_item_defid)) = imported_item_path.res.first()
-                && cx.tcx.item_name(*imported_item_defid).as_str() == str
+                // use `present_items` because it could be in any of type_ns, value_ns, macro_ns
+                && let Some(Res::Def(_, imported_item_defid)) = imported_item_path.res.value_ns
+                && cx.tcx.item_name(imported_item_defid).as_str() == str
             {
                 return;
             }