check mut: from hir to mir

just because less lines

Author: lengyijun

clippy_lints/src/explicit_reinitialization.rs

@@ -1,7 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_opt;
-use clippy_utils::visitors::for_each_local_use_after_expr;
-use clippy_utils::{fn_has_unsatisfiable_preds, get_parent_expr, is_from_proc_macro};
+use clippy_utils::{fn_has_unsatisfiable_preds, is_from_proc_macro};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_data_structures::graph::iterate::DepthFirstSearch;
@@ -11,16 +10,14 @@ use rustc_hir::def::Res;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::{
     Closure, Expr, ExprKind, HirId, ImplItem, ImplItemKind, Item, ItemKind, Mutability, Node, Path, PathSegment, QPath,
-    StmtKind, TraitFn, TraitItem, TraitItemKind, UnOp,
+    StmtKind, TraitFn, TraitItem, TraitItemKind,
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::mir::visit::{PlaceContext, Visitor};
+use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{self, BasicBlock, Body, Local, Location, Place, Statement, Terminator};
 use rustc_session::{declare_lint_pass, declare_tool_lint, Session};
 use rustc_span::Span;
-use std::collections::BTreeSet;
-use std::ops::ControlFlow;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -75,7 +72,7 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitReinitialization {
                                     None,
                                     Path {
                                         segments: [PathSegment { args: None, .. }],
-                                        res: Res::Local(local_id),
+                                        res: Res::Local(_),
                                         ..
                                     },
                                 )),
@@ -85,7 +82,6 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitReinitialization {
                         right,
                         _,
                     ),
-                hir_id: expr_id,
                 ..
             },
         ) = stmt.kind
@@ -118,65 +114,14 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitReinitialization {
 
         assert!(start_location.dominates(location, dominators));
 
-        if dominate_all_usage(mir, dominators, local, start_location) {
-            // copy from `vec_init_then_push.rs`
-            let mut needs_mut = false;
-            let _ = for_each_local_use_after_expr(cx, *local_id, *expr_id, |e| {
-                let Some(parent) = get_parent_expr(cx, e) else {
-                    return ControlFlow::Continue(());
-                };
-                let adjusted_ty = cx.typeck_results().expr_ty_adjusted(e);
-                let adjusted_mut = adjusted_ty.ref_mutability().unwrap_or(Mutability::Not);
-                needs_mut |= adjusted_mut == Mutability::Mut;
-                match parent.kind {
-                    ExprKind::AddrOf(_, Mutability::Mut, _) => {
-                        needs_mut = true;
-                        return ControlFlow::Break(true);
-                    },
-                    ExprKind::Unary(UnOp::Deref, _) | ExprKind::Index(..) if !needs_mut => {
-                        let mut last_place = parent;
-                        while let Some(parent) = get_parent_expr(cx, last_place) {
-                            if matches!(parent.kind, ExprKind::Unary(UnOp::Deref, _) | ExprKind::Field(..))
-                                || matches!(parent.kind, ExprKind::Index(e, _, _) if e.hir_id == last_place.hir_id)
-                            {
-                                last_place = parent;
-                            } else {
-                                break;
-                            }
-                        }
-                        needs_mut |= cx.typeck_results().expr_ty_adjusted(last_place).ref_mutability()
-                            == Some(Mutability::Mut)
-                            || get_parent_expr(cx, last_place)
-                                .map_or(false, |e| matches!(e.kind, ExprKind::AddrOf(_, Mutability::Mut, _)));
-                    },
-                    ExprKind::MethodCall(_, recv, ..)
-                        if recv.hir_id == e.hir_id
-                            && adjusted_mut == Mutability::Mut
-                            && !adjusted_ty.peel_refs().is_slice() =>
-                    {
-                        // No need to set `needs_mut` to true. The receiver will be either explicitly borrowed, or it
-                        // will be implicitly borrowed via an adjustment. Both of these cases
-                        // are already handled by this point.
-                        return ControlFlow::Break(true);
-                    },
-                    ExprKind::Assign(lhs, ..) if e.hir_id == lhs.hir_id => {
-                        needs_mut = true;
-                        return ControlFlow::Break(false);
-                    },
-                    _ => (),
-                }
-                ControlFlow::Continue(())
-            });
-
-            let mut_str = if needs_mut { "mut " } else { "" };
-
+        if let Some(mutability) = dominate_all_usage(mir, dominators, local, location) {
             span_lint_and_sugg(
                 cx,
                 EXPLICIT_REINITIALIZATION,
                 stmt.span,
                 "create a fresh variable is more explicit",
                 "create a fresh variable instead of reinitialization",
-                format!("let {mut_str}{snip}"),
+                format!("let {}{snip}", mutability.prefix_str()),
                 Applicability::MachineApplicable,
             );
         }
@@ -386,42 +331,71 @@ fn search_mir_by_span(
     accurate_visitor.result
 }
 
+// None: doesn't dominate all usage
+// Some(Mut): dominate all usage, and a mut usage found
+// Some(Not); dominate all uagee, and no muge usage found
 fn dominate_all_usage(
     mir: &mir::Body<'_>,
     dominators: &Dominators<BasicBlock>,
     local: Local,
     start_location: Location,
-) -> bool {
+) -> Option<Mutability> {
     let mut dfs = DepthFirstSearch::new(&mir.basic_blocks);
     for successor in mir.basic_blocks.successors(start_location.block) {
         dfs.push_start_node(successor);
     }
     let reachable_bb: FxHashSet<BasicBlock> = dfs.collect();
-    find_usage(mir, local)
+
+    let mut res = Mutability::Not;
+
+    for (location, mutability) in find_usage(mir, local)
         .into_iter()
-        .filter(|location| reachable_bb.contains(&location.block))
-        .filter(|location| !mir.basic_blocks[location.block].is_cleanup)
-        .all(|location| start_location.dominates(location, dominators))
+        .filter(|(location, _)| !mir.basic_blocks[location.block].is_cleanup)
+    {
+        if reachable_bb.contains(&location.block) {
+            if !start_location.dominates(location, dominators) {
+                return None;
+            }
+            if location != start_location && mutability == Mutability::Mut {
+                res = Mutability::Mut;
+            }
+        } else if location.block == start_location.block
+            && location.statement_index > start_location.statement_index
+            && mutability == Mutability::Mut
+        {
+            res = Mutability::Mut;
+        }
+    }
+    Some(res)
 }
 
 // copy from https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc_borrowck/diagnostics/find_all_local_uses.rs.html#1-29
-fn find_usage(body: &Body<'_>, local: Local) -> BTreeSet<Location> {
+fn find_usage(body: &Body<'_>, local: Local) -> FxHashSet<(Location, Mutability)> {
     struct AllLocalUsesVisitor {
         for_local: Local,
-        uses: BTreeSet<Location>,
+        uses: FxHashSet<(Location, Mutability)>,
     }
 
     impl<'tcx> Visitor<'tcx> for AllLocalUsesVisitor {
-        fn visit_local(&mut self, local: Local, _context: PlaceContext, location: Location) {
+        fn visit_local(&mut self, local: Local, context: PlaceContext, location: Location) {
             if local == self.for_local {
-                self.uses.insert(location);
+                match context {
+                    PlaceContext::NonMutatingUse(_)
+                    | PlaceContext::NonUse(_)
+                    | PlaceContext::MutatingUse(MutatingUseContext::Drop) => {
+                        self.uses.insert((location, Mutability::Not));
+                    },
+                    PlaceContext::MutatingUse(_) => {
+                        self.uses.insert((location, Mutability::Mut));
+                    },
+                }
             }
         }
     }
 
     let mut visitor = AllLocalUsesVisitor {
         for_local: local,
-        uses: BTreeSet::default(),
+        uses: FxHashSet::default(),
     };
     visitor.visit_body(body);
     visitor.uses