Fix: avoid changing drop order

clippy_lints/src/redundant_locals.rs

@@ -3,7 +3,7 @@ use clippy_utils::is_from_proc_macro;
 use clippy_utils::ty::needs_ordered_drop;
 use rustc_ast::Mutability;
 use rustc_hir::def::Res;
-use rustc_hir::{BindingAnnotation, ByRef, Expr, ExprKind, HirId, Local, Node, Pat, PatKind, QPath};
+use rustc_hir::{BindingAnnotation, ByRef, ExprKind, HirId, Local, Node, Pat, PatKind, QPath};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -66,7 +66,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantLocals {
             // the local does not change the effect of assignments to the binding. see #11290
             if !affects_assignments(cx, mutability, binding_id, local.hir_id);
             // the local does not affect the code's drop behavior
-            if !affects_drop_behavior(cx, binding_id, local.hir_id, expr);
+            if !needs_ordered_drop(cx, cx.typeck_results().expr_ty(expr));
             // the local is user-controlled
             if !in_external_macro(cx.sess(), local.span);
             if !is_from_proc_macro(cx, expr);
@@ -104,13 +104,3 @@ fn affects_assignments(cx: &LateContext<'_>, mutability: Mutability, bind: HirId
     // the binding is mutable and the rebinding is in a different scope than the original binding
     mutability == Mutability::Mut && hir.get_enclosing_scope(bind) != hir.get_enclosing_scope(rebind)
 }
-
-/// Check if a rebinding of a local affects the code's drop behavior.
-fn affects_drop_behavior<'tcx>(cx: &LateContext<'tcx>, bind: HirId, rebind: HirId, rebind_expr: &Expr<'tcx>) -> bool {
-    let hir = cx.tcx.hir();
-
-    // the rebinding is in a different scope than the original binding
-    // and the type of the binding cares about drop order
-    hir.get_enclosing_scope(bind) != hir.get_enclosing_scope(rebind)
-        && needs_ordered_drop(cx, cx.typeck_results().expr_ty(rebind_expr))
-}

tests/ui/redundant_locals.rs

@@ -118,3 +118,40 @@ fn macros() {
         let x = x;
     }
 }
+
+struct WithDrop(usize);
+impl Drop for WithDrop {
+    fn drop(&mut self) {}
+}
+
+struct InnerDrop(WithDrop);
+
+struct ComposeDrop {
+    d: WithDrop,
+}
+
+struct WithoutDrop(usize);
+
+fn drop_trait() {
+    let a = WithDrop(1);
+    let b = WithDrop(2);
+    let a = a;
+}
+
+fn without_drop() {
+    let a = WithoutDrop(1);
+    let b = WithoutDrop(2);
+    let a = a;
+}
+
+fn drop_inner() {
+    let a = InnerDrop(WithDrop(1));
+    let b = InnerDrop(WithDrop(2));
+    let a = a;
+}
+
+fn drop_compose() {
+    let a = ComposeDrop { d: WithDrop(1) };
+    let b = ComposeDrop { d: WithDrop(1) };
+    let a = a;
+}

tests/ui/redundant_locals.stderr

@@ -133,5 +133,16 @@ LL |         let x = x;
    |
    = help: remove the redefinition of `x`
 
-error: aborting due to 13 previous errors
+error: redundant redefinition of a binding
+  --> $DIR/redundant_locals.rs:142:9
+   |
+LL |     let a = WithoutDrop(1);
+   |         ^
+LL |     let b = WithoutDrop(2);
+LL |     let a = a;
+   |     ^^^^^^^^^^
+   |
+   = help: remove the redefinition of `a`
+
+error: aborting due to 14 previous errors