Don't lint cmp_owned when From::from results in a copy type.

Author: Jarcho

clippy_lints/src/misc.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then, span_lint_hir_and_then};
 use clippy_utils::source::{snippet, snippet_opt};
-use clippy_utils::ty::implements_trait;
+use clippy_utils::ty::{implements_trait, is_copy};
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
@@ -584,7 +584,11 @@ fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left:
         ExprKind::Call(path, [arg])
             if path_def_id(cx, path)
                 .and_then(|id| match_any_def_paths(cx, id, &[&paths::FROM_STR_METHOD, &paths::FROM_FROM]))
-                .is_some() =>
+                .map_or(false, |idx| match idx {
+                    0 => true,
+                    1 => !is_copy(cx, typeck.expr_ty(expr)),
+                    _ => false,
+                }) =>
         {
             (arg, arg.span)
         },

tests/ui/cmp_owned/without_suggestion.rs

@@ -9,6 +9,10 @@ fn main() {
     let x = &&Baz;
     let y = &Baz;
     y.to_owned() == **x;
+
+    let x = 0u32;
+    let y = U32Wrapper(x);
+    let _ = U32Wrapper::from(x) == y;
 }
 
 struct Foo;
@@ -51,3 +55,21 @@ impl std::borrow::Borrow<Foo> for Bar {
         &FOO
     }
 }
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+struct U32Wrapper(u32);
+impl From<u32> for U32Wrapper {
+    fn from(x: u32) -> Self {
+        Self(x)
+    }
+}
+impl PartialEq<u32> for U32Wrapper {
+    fn eq(&self, other: &u32) -> bool {
+        self.0 == *other
+    }
+}
+impl PartialEq<U32Wrapper> for u32 {
+    fn eq(&self, other: &U32Wrapper) -> bool {
+        *self == other.0
+    }
+}

tests/ui/cmp_owned/without_suggestion.stderr

@@ -13,7 +13,7 @@ LL |     y.to_owned() == **x;
    |     ^^^^^^^^^^^^^^^^^^^ try implementing the comparison without allocating
 
 error: this creates an owned instance just for comparison
-  --> $DIR/without_suggestion.rs:18:9
+  --> $DIR/without_suggestion.rs:22:9
    |
 LL |         self.to_owned() == *other
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^ try implementing the comparison without allocating