Lint explicit_auto_deref without a leading borrow

Author: Jarcho

clippy_lints/src/dereference.rs

@@ -246,6 +246,8 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing {
             (None, kind) => {
                 let expr_ty = typeck.expr_ty(expr);
                 let (position, parent_ctxt) = get_expr_position(cx, expr);
+                let (stability, adjustments) = walk_parents(cx, expr);
+
                 match kind {
                     RefOp::Deref => {
                         if let Position::FieldAccess(name) = position
@@ -255,6 +257,11 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing {
                                 State::ExplicitDerefField { name },
                                 StateData { span: expr.span, hir_id: expr.hir_id },
                             ));
+                        } else if stability.is_deref_stable() {
+                            self.state = Some((
+                                State::ExplicitDeref { deref_span: expr.span, deref_hir_id: expr.hir_id },
+                                StateData { span: expr.span, hir_id: expr.hir_id },
+                            ));
                         }
                     }
                     RefOp::Method(target_mut)
@@ -278,7 +285,6 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing {
                         ));
                     },
                     RefOp::AddrOf => {
-                        let (stability, adjustments) = walk_parents(cx, expr);
                         // Find the number of times the borrow is auto-derefed.
                         let mut iter = adjustments.iter();
                         let mut deref_count = 0usize;
@@ -632,6 +638,7 @@ impl AutoDerefStability {
 /// Walks up the parent expressions attempting to determine both how stable the auto-deref result
 /// is, and which adjustments will be applied to it. Note this will not consider auto-borrow
 /// locations as those follow different rules.
+#[allow(clippy::too_many_lines)]
 fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (AutoDerefStability, &'tcx [Adjustment<'tcx>]) {
     let mut adjustments = [].as_slice();
     let stability = walk_to_expr_usage(cx, e, &mut |node, child_id| {
@@ -643,16 +650,26 @@ fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (AutoDerefSt
             Node::Local(Local { ty: Some(ty), .. }) => Some(binding_ty_auto_deref_stability(ty)),
             Node::Item(&Item {
                 kind: ItemKind::Static(..) | ItemKind::Const(..),
+                def_id,
                 ..
             })
             | Node::TraitItem(&TraitItem {
                 kind: TraitItemKind::Const(..),
+                def_id,
                 ..
             })
             | Node::ImplItem(&ImplItem {
                 kind: ImplItemKind::Const(..),
+                def_id,
                 ..
-            }) => Some(AutoDerefStability::Deref),
+            }) => {
+                let ty = cx.tcx.type_of(def_id);
+                Some(if ty.is_ref() {
+                    AutoDerefStability::None
+                } else {
+                    AutoDerefStability::Deref
+                })
+            },
 
             Node::Item(&Item {
                 kind: ItemKind::Fn(..),
@@ -670,7 +687,9 @@ fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (AutoDerefSt
                 ..
             }) => {
                 let output = cx.tcx.fn_sig(def_id.to_def_id()).skip_binder().output();
-                Some(if output.has_placeholders() || output.has_opaque_types() {
+                Some(if !output.is_ref() {
+                    AutoDerefStability::None
+                } else if output.has_placeholders() || output.has_opaque_types() {
                     AutoDerefStability::Reborrow
                 } else {
                     AutoDerefStability::Deref
@@ -684,7 +703,9 @@ fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (AutoDerefSt
                         .fn_sig(cx.tcx.hir().body_owner_def_id(cx.enclosing_body.unwrap()))
                         .skip_binder()
                         .output();
-                    Some(if output.has_placeholders() || output.has_opaque_types() {
+                    Some(if !output.is_ref() {
+                        AutoDerefStability::None
+                    } else if output.has_placeholders() || output.has_opaque_types() {
                         AutoDerefStability::Reborrow
                     } else {
                         AutoDerefStability::Deref

tests/ui/explicit_auto_deref.fixed

@@ -6,6 +6,7 @@
     unused_braces,
     clippy::borrowed_box,
     clippy::needless_borrow,
+    clippy::needless_return,
     clippy::ptr_arg,
     clippy::redundant_field_names,
     clippy::too_many_arguments,
@@ -184,4 +185,17 @@ fn main() {
     }
     let s6 = S6 { foo: S5 { foo: 5 } };
     let _ = (*s6).foo; // Don't lint. `S6` also has a field named `foo`
+
+    let ref_str = &"foo";
+    let _ = f_str(ref_str);
+    let ref_ref_str = &ref_str;
+    let _ = f_str(ref_ref_str);
+
+    fn _f5(x: &u32) -> u32 {
+        if true {
+            *x
+        } else {
+            return *x;
+        }
+    }
 }

tests/ui/explicit_auto_deref.rs

@@ -6,6 +6,7 @@
     unused_braces,
     clippy::borrowed_box,
     clippy::needless_borrow,
+    clippy::needless_return,
     clippy::ptr_arg,
     clippy::redundant_field_names,
     clippy::too_many_arguments,
@@ -184,4 +185,17 @@ fn main() {
     }
     let s6 = S6 { foo: S5 { foo: 5 } };
     let _ = (*s6).foo; // Don't lint. `S6` also has a field named `foo`
+
+    let ref_str = &"foo";
+    let _ = f_str(*ref_str);
+    let ref_ref_str = &ref_str;
+    let _ = f_str(**ref_ref_str);
+
+    fn _f5(x: &u32) -> u32 {
+        if true {
+            *x
+        } else {
+            return *x;
+        }
+    }
 }

tests/ui/explicit_auto_deref.stderr

@@ -168,5 +168,17 @@ error: deref which would be done by auto-deref
 LL |     let _ = (**b).foo;
    |             ^^^^^ help: try this: `b`
 
-error: aborting due to 28 previous errors
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:189:19
+   |
+LL |     let _ = f_str(*ref_str);
+   |                   ^^^^^^^^ help: try this: `ref_str`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:191:19
+   |
+LL |     let _ = f_str(**ref_ref_str);
+   |                   ^^^^^^^^^^^^^ help: try this: `ref_ref_str`
+
+error: aborting due to 30 previous errors
 

tests/ui/needless_borrow_pat.rs

@@ -1,7 +1,7 @@
 // FIXME: run-rustfix waiting on multi-span suggestions
 
 #![warn(clippy::needless_borrow)]
-#![allow(clippy::needless_borrowed_reference)]
+#![allow(clippy::needless_borrowed_reference, clippy::explicit_auto_deref)]
 
 fn f1(_: &str) {}
 macro_rules! m1 {

tests/ui/ref_binding_to_reference.rs

@@ -2,7 +2,7 @@
 
 #![feature(lint_reasons)]
 #![warn(clippy::ref_binding_to_reference)]
-#![allow(clippy::needless_borrowed_reference)]
+#![allow(clippy::needless_borrowed_reference, clippy::explicit_auto_deref)]
 
 fn f1(_: &str) {}
 macro_rules! m2 {

tests/ui/search_is_some_fixable_none.fixed

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(dead_code)]
+#![allow(dead_code, clippy::explicit_auto_deref)]
 #![warn(clippy::search_is_some)]
 
 fn main() {

tests/ui/search_is_some_fixable_none.rs

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(dead_code)]
+#![allow(dead_code, clippy::explicit_auto_deref)]
 #![warn(clippy::search_is_some)]
 
 fn main() {

tests/ui/search_is_some_fixable_some.fixed

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(dead_code)]
+#![allow(dead_code, clippy::explicit_auto_deref)]
 #![warn(clippy::search_is_some)]
 
 fn main() {

tests/ui/search_is_some_fixable_some.rs

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(dead_code)]
+#![allow(dead_code, clippy::explicit_auto_deref)]
 #![warn(clippy::search_is_some)]
 
 fn main() {