cmp_owned: reverse operands if necessary

clippy_lints/src/misc.rs

@@ -371,8 +371,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MiscLints {
                 if op.is_comparison() {
                     check_nan(cx, left, expr);
                     check_nan(cx, right, expr);
-                    check_to_owned(cx, left, right);
-                    check_to_owned(cx, right, left);
+                    check_to_owned(cx, left, right, true);
+                    check_to_owned(cx, right, left, false);
                 }
                 if (op == BinOpKind::Eq || op == BinOpKind::Ne) && (is_float(cx, left) || is_float(cx, right)) {
                     if is_allowed(cx, left) || is_allowed(cx, right) {
@@ -570,20 +570,30 @@ fn is_array(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
     matches!(&walk_ptrs_ty(cx.tables.expr_ty(expr)).kind, ty::Array(_, _))
 }
 
-fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>) {
-    fn symmetric_partial_eq<'tcx>(cx: &LateContext<'_, 'tcx>, lhs: Ty<'tcx>, rhs: Ty<'tcx>) -> bool {
-        if let Some(trait_def_id) = cx.tcx.lang_items().eq_trait() {
-            return implements_trait(cx, lhs, trait_def_id, &[rhs.into()])
-                && implements_trait(cx, rhs, trait_def_id, &[lhs.into()]);
-        }
+fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool) {
+    #[derive(Default)]
+    struct EqImpl {
+        ty_eq_other: bool,
+        other_eq_ty: bool,
+    }
 
-        false
+    impl EqImpl {
+        fn is_implemented(&self) -> bool {
+            self.ty_eq_other || self.other_eq_ty
+        }
+    }
+
+    fn symmetric_partial_eq<'tcx>(cx: &LateContext<'_, 'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> Option<EqImpl> {
+        cx.tcx.lang_items().eq_trait().map(|def_id| EqImpl {
+            ty_eq_other: implements_trait(cx, ty, def_id, &[other.into()]),
+            other_eq_ty: implements_trait(cx, other, def_id, &[ty.into()]),
+        })
     }
 
     let (arg_ty, snip) = match expr.kind {
         ExprKind::MethodCall(.., ref args, _) if args.len() == 1 => {
             if match_trait_method(cx, expr, &paths::TO_STRING) || match_trait_method(cx, expr, &paths::TO_OWNED) {
-                (cx.tables.expr_ty_adjusted(&args[0]), snippet(cx, args[0].span, ".."))
+                (cx.tables.expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
             } else {
                 return;
             }
@@ -591,7 +601,7 @@ fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>) {
         ExprKind::Call(ref path, ref v) if v.len() == 1 => {
             if let ExprKind::Path(ref path) = path.kind {
                 if match_qpath(path, &["String", "from_str"]) || match_qpath(path, &["String", "from"]) {
-                    (cx.tables.expr_ty_adjusted(&v[0]), snippet(cx, v[0].span, ".."))
+                    (cx.tables.expr_ty(&v[0]), snippet(cx, v[0].span, ".."))
                 } else {
                     return;
                 }
@@ -602,24 +612,19 @@ fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>) {
         _ => return,
     };
 
-    let other_ty = cx.tables.expr_ty_adjusted(other);
+    let other_ty = cx.tables.expr_ty(other);
 
-    let deref_arg_impl_partial_eq_other = arg_ty
+    let without_deref = symmetric_partial_eq(cx, arg_ty, other_ty).unwrap_or_default();
+    let with_deref = arg_ty
         .builtin_deref(true)
-        .map_or(false, |tam| symmetric_partial_eq(cx, tam.ty, other_ty));
-    let arg_impl_partial_eq_deref_other = other_ty
-        .builtin_deref(true)
-        .map_or(false, |tam| symmetric_partial_eq(cx, arg_ty, tam.ty));
-    let arg_impl_partial_eq_other = symmetric_partial_eq(cx, arg_ty, other_ty);
+        .and_then(|tam| symmetric_partial_eq(cx, tam.ty, other_ty))
+        .unwrap_or_default();
 
-    if !deref_arg_impl_partial_eq_other && !arg_impl_partial_eq_deref_other && !arg_impl_partial_eq_other {
+    if !with_deref.is_implemented() && !without_deref.is_implemented() {
         return;
     }
 
-    let other_gets_derefed = match other.kind {
-        ExprKind::Unary(UnOp::UnDeref, _) => true,
-        _ => false,
-    };
+    let other_gets_derefed = matches!(other.kind, ExprKind::Unary(UnOp::UnDeref, _));
 
     let lint_span = if other_gets_derefed {
         expr.span.to(other.span)
@@ -639,18 +644,34 @@ fn check_to_owned(cx: &LateContext<'_, '_>, expr: &Expr<'_>, other: &Expr<'_>) {
                 return;
             }
 
-            let try_hint = if deref_arg_impl_partial_eq_other {
-                // suggest deref on the left
-                format!("*{}", snip)
+            let expr_snip;
+            let eq_impl;
+            if with_deref.is_implemented() {
+                expr_snip = format!("*{}", snip);
+                eq_impl = with_deref;
             } else {
-                // suggest dropping the to_owned on the left
-                snip.to_string()
+                expr_snip = snip.to_string();
+                eq_impl = without_deref;
             };
 
+            let span;
+            let hint;
+            if (eq_impl.ty_eq_other && left) || (eq_impl.other_eq_ty && !left) {
+                span = expr.span;
+                hint = expr_snip;
+            } else {
+                span = expr.span.to(other.span);
+                if eq_impl.ty_eq_other {
+                    hint = format!("{} == {}", expr_snip, snippet(cx, other.span, ".."));
+                } else {
+                    hint = format!("{} == {}", snippet(cx, other.span, ".."), expr_snip);
+                }
+            }
+
             diag.span_suggestion(
-                lint_span,
+                span,
                 "try",
-                try_hint,
+                hint,
                 Applicability::MachineApplicable, // snippet
             );
         },

tests/ui/cmp_owned/asymmetric_partial_eq.fixed

@@ -0,0 +1,93 @@
+// run-rustfix
+#![allow(unused, clippy::redundant_clone)] // See #5700
+
+// Define the types in each module to avoid trait impls leaking between modules.
+macro_rules! impl_types {
+    () => {
+        #[derive(PartialEq)]
+        pub struct Owned;
+
+        pub struct Borrowed;
+
+        impl ToOwned for Borrowed {
+            type Owned = Owned;
+            fn to_owned(&self) -> Owned {
+                Owned {}
+            }
+        }
+
+        impl std::borrow::Borrow<Borrowed> for Owned {
+            fn borrow(&self) -> &Borrowed {
+                static VALUE: Borrowed = Borrowed {};
+                &VALUE
+            }
+        }
+    };
+}
+
+// Only Borrowed == Owned is implemented
+mod borrowed_eq_owned {
+    impl_types!();
+
+    impl PartialEq<Owned> for Borrowed {
+        fn eq(&self, _: &Owned) -> bool {
+            true
+        }
+    }
+
+    pub fn compare() {
+        let owned = Owned {};
+        let borrowed = Borrowed {};
+
+        if borrowed == owned {}
+        if borrowed == owned {}
+    }
+}
+
+// Only Owned == Borrowed is implemented
+mod owned_eq_borrowed {
+    impl_types!();
+
+    impl PartialEq<Borrowed> for Owned {
+        fn eq(&self, _: &Borrowed) -> bool {
+            true
+        }
+    }
+
+    fn compare() {
+        let owned = Owned {};
+        let borrowed = Borrowed {};
+
+        if owned == borrowed {}
+        if owned == borrowed {}
+    }
+}
+
+mod issue_4874 {
+    impl_types!();
+
+    // NOTE: PartialEq<Borrowed> for T can't be implemented due to the orphan rules
+    impl<T> PartialEq<T> for Borrowed
+    where
+        T: AsRef<str> + ?Sized,
+    {
+        fn eq(&self, _: &T) -> bool {
+            true
+        }
+    }
+
+    impl std::fmt::Display for Borrowed {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            write!(f, "borrowed")
+        }
+    }
+
+    fn compare() {
+        let borrowed = Borrowed {};
+
+        if borrowed == "Hi" {}
+        if borrowed == "Hi" {}
+    }
+}
+
+fn main() {}

tests/ui/cmp_owned/asymmetric_partial_eq.rs

@@ -0,0 +1,93 @@
+// run-rustfix
+#![allow(unused, clippy::redundant_clone)] // See #5700
+
+// Define the types in each module to avoid trait impls leaking between modules.
+macro_rules! impl_types {
+    () => {
+        #[derive(PartialEq)]
+        pub struct Owned;
+
+        pub struct Borrowed;
+
+        impl ToOwned for Borrowed {
+            type Owned = Owned;
+            fn to_owned(&self) -> Owned {
+                Owned {}
+            }
+        }
+
+        impl std::borrow::Borrow<Borrowed> for Owned {
+            fn borrow(&self) -> &Borrowed {
+                static VALUE: Borrowed = Borrowed {};
+                &VALUE
+            }
+        }
+    };
+}
+
+// Only Borrowed == Owned is implemented
+mod borrowed_eq_owned {
+    impl_types!();
+
+    impl PartialEq<Owned> for Borrowed {
+        fn eq(&self, _: &Owned) -> bool {
+            true
+        }
+    }
+
+    pub fn compare() {
+        let owned = Owned {};
+        let borrowed = Borrowed {};
+
+        if borrowed.to_owned() == owned {}
+        if owned == borrowed.to_owned() {}
+    }
+}
+
+// Only Owned == Borrowed is implemented
+mod owned_eq_borrowed {
+    impl_types!();
+
+    impl PartialEq<Borrowed> for Owned {
+        fn eq(&self, _: &Borrowed) -> bool {
+            true
+        }
+    }
+
+    fn compare() {
+        let owned = Owned {};
+        let borrowed = Borrowed {};
+
+        if owned == borrowed.to_owned() {}
+        if borrowed.to_owned() == owned {}
+    }
+}
+
+mod issue_4874 {
+    impl_types!();
+
+    // NOTE: PartialEq<Borrowed> for T can't be implemented due to the orphan rules
+    impl<T> PartialEq<T> for Borrowed
+    where
+        T: AsRef<str> + ?Sized,
+    {
+        fn eq(&self, _: &T) -> bool {
+            true
+        }
+    }
+
+    impl std::fmt::Display for Borrowed {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            write!(f, "borrowed")
+        }
+    }
+
+    fn compare() {
+        let borrowed = Borrowed {};
+
+        if "Hi" == borrowed.to_string() {}
+        if borrowed.to_string() == "Hi" {}
+    }
+}
+
+fn main() {}

tests/ui/cmp_owned/asymmetric_partial_eq.stderr

@@ -0,0 +1,46 @@
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:42:12
+   |
+LL |         if borrowed.to_owned() == owned {}
+   |            ^^^^^^^^^^^^^^^^^^^ help: try: `borrowed`
+   |
+   = note: `-D clippy::cmp-owned` implied by `-D warnings`
+
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:43:21
+   |
+LL |         if owned == borrowed.to_owned() {}
+   |            ---------^^^^^^^^^^^^^^^^^^^
+   |            |
+   |            help: try: `borrowed == owned`
+
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:61:21
+   |
+LL |         if owned == borrowed.to_owned() {}
+   |                     ^^^^^^^^^^^^^^^^^^^ help: try: `borrowed`
+
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:62:12
+   |
+LL |         if borrowed.to_owned() == owned {}
+   |            ^^^^^^^^^^^^^^^^^^^---------
+   |            |
+   |            help: try: `owned == borrowed`
+
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:88:20
+   |
+LL |         if "Hi" == borrowed.to_string() {}
+   |            --------^^^^^^^^^^^^^^^^^^^^
+   |            |
+   |            help: try: `borrowed == "Hi"`
+
+error: this creates an owned instance just for comparison
+  --> $DIR/asymmetric_partial_eq.rs:89:12
+   |
+LL |         if borrowed.to_string() == "Hi" {}
+   |            ^^^^^^^^^^^^^^^^^^^^ help: try: `borrowed`
+
+error: aborting due to 6 previous errors
+

tests/ui/cmp_owned/issue_4874.rs

@@ -1,51 +0,0 @@
-#![allow(clippy::redundant_clone)] // See #5700
-
-#[derive(PartialEq)]
-struct Foo;
-
-struct Bar;
-
-impl std::fmt::Display for Bar {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "bar")
-    }
-}
-
-// NOTE: PartialEq<Bar> for T can't be implemented due to the orphan rules
-impl<T> PartialEq<T> for Bar
-where
-    T: AsRef<str> + ?Sized,
-{
-    fn eq(&self, _: &T) -> bool {
-        true
-    }
-}
-
-// NOTE: PartialEq<Bar> for Foo is not implemented
-impl PartialEq<Foo> for Bar {
-    fn eq(&self, _: &Foo) -> bool {
-        true
-    }
-}
-
-impl ToOwned for Bar {
-    type Owned = Foo;
-    fn to_owned(&self) -> Foo {
-        Foo
-    }
-}
-
-impl std::borrow::Borrow<Bar> for Foo {
-    fn borrow(&self) -> &Bar {
-        static BAR: Bar = Bar;
-        &BAR
-    }
-}
-
-fn main() {
-    let b = Bar {};
-    if "Hi" == b.to_string() {}
-
-    let f = Foo {};
-    if f == b.to_owned() {}
-}