Don't emit needless_pass_by_ref_mut if the variable is used in an u…

…nsafe block or function

clippy_lints/src/needless_pass_by_ref_mut.rs

@@ -7,7 +7,8 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_qpath, FnKind, Visitor};
 use rustc_hir::{
-    Body, Closure, Expr, ExprKind, FnDecl, HirId, HirIdMap, HirIdSet, Impl, ItemKind, Mutability, Node, PatKind, QPath,
+    BlockCheckMode, Body, Closure, Expr, ExprKind, FnDecl, HirId, HirIdMap, HirIdSet, Impl, ItemKind, Mutability, Node,
+    PatKind, QPath,
 };
 use rustc_hir_typeck::expr_use_visitor as euv;
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
@@ -139,13 +140,23 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessPassByRefMut<'tcx> {
         let hir_id = cx.tcx.hir().local_def_id_to_hir_id(fn_def_id);
         let is_async = match kind {
             FnKind::ItemFn(.., header) => {
+                if header.is_unsafe() {
+                    // We don't check unsafe functions.
+                    return;
+                }
                 let attrs = cx.tcx.hir().attrs(hir_id);
                 if header.abi != Abi::Rust || requires_exact_signature(attrs) {
                     return;
                 }
                 header.is_async()
             },
-            FnKind::Method(.., sig) => sig.header.is_async(),
+            FnKind::Method(.., sig) => {
+                if sig.header.is_unsafe() {
+                    // We don't check unsafe functions.
+                    return;
+                }
+                sig.header.is_async()
+            },
             FnKind::Closure => return,
         };
 
@@ -304,6 +315,23 @@ impl<'tcx> MutablyUsedVariablesCtxt<'tcx> {
         }
         self.aliases.insert(alias, target);
     }
+
+    // The goal here is to find if the current scope is unsafe or not. It stops when it finds
+    // a function or an unsafe block.
+    fn is_in_unsafe_block(&self, mut item: HirId) -> bool {
+        let hir = self.tcx.hir();
+        while let Some(parent) = hir.get_enclosing_scope(item) {
+            if let Some(fn_sig) = hir.fn_sig_by_hir_id(parent) {
+                return fn_sig.header.is_unsafe();
+            } else if let Some(Node::Block(block)) = hir.find(parent) {
+                if matches!(block.rules, BlockCheckMode::UnsafeBlock(_)) {
+                    return true;
+                }
+            }
+            item = parent;
+        }
+        false
+    }
 }
 
 impl<'tcx> euv::Delegate<'tcx> for MutablyUsedVariablesCtxt<'tcx> {
@@ -327,6 +355,10 @@ impl<'tcx> euv::Delegate<'tcx> for MutablyUsedVariablesCtxt<'tcx> {
                 && matches!(base_ty.ref_mutability(), Some(Mutability::Mut))
             {
                 self.add_mutably_used_var(*vid);
+            } else if self.is_in_unsafe_block(*vid) {
+                // If we are in an unsafe block, any operation on this variable must not be warned
+                // upon!
+                self.add_mutably_used_var(*vid);
             }
             self.prev_bind = None;
             self.prev_move_to_closure.remove(vid);
@@ -355,6 +387,10 @@ impl<'tcx> euv::Delegate<'tcx> for MutablyUsedVariablesCtxt<'tcx> {
                 || (borrow == ty::BorrowKind::UniqueImmBorrow && base_ty.ref_mutability() == Some(Mutability::Mut))
             {
                 self.add_mutably_used_var(*vid);
+            } else if self.is_in_unsafe_block(*vid) {
+                // If we are in an unsafe block, any operation on this variable must not be warned
+                // upon!
+                self.add_mutably_used_var(*vid);
             }
         } else if borrow == ty::ImmBorrow {
             // If there is an `async block`, it'll contain a call to a closure which we need to