Reduce unnecessary work in cmp_owned

Author: Jarcho

clippy_lints/src/misc.rs

@@ -20,8 +20,8 @@ use rustc_span::symbol::sym;
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
-    get_item_name, get_parent_expr, in_constant, is_diag_trait_item, is_integer_const, iter_input_pats,
-    last_path_segment, match_any_def_paths, path_def_id, paths, unsext, SpanlessEq,
+    get_item_name, get_parent_expr, in_constant, is_integer_const, iter_input_pats, last_path_segment,
+    match_any_def_paths, path_def_id, paths, unsext, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -569,33 +569,30 @@ fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left:
         })
     }
 
-    let (arg_ty, snip) = match expr.kind {
-        ExprKind::MethodCall(.., args, _) if args.len() == 1 => {
-            if_chain!(
-                if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
-                if is_diag_trait_item(cx, expr_def_id, sym::ToString)
-                    || is_diag_trait_item(cx, expr_def_id, sym::ToOwned);
-                then {
-                    (cx.typeck_results().expr_ty(&args[0]), snippet(cx, args[0].span, ".."))
-                } else {
-                    return;
-                }
-            )
+    let typeck = cx.typeck_results();
+    let (arg, arg_span) = match expr.kind {
+        ExprKind::MethodCall(.., [arg], _)
+            if typeck
+                .type_dependent_def_id(expr.hir_id)
+                .and_then(|id| cx.tcx.trait_of_item(id))
+                .map_or(false, |id| {
+                    matches!(cx.tcx.get_diagnostic_name(id), Some(sym::ToString | sym::ToOwned))
+                }) =>
+        {
+            (arg, arg.span)
         },
-        ExprKind::Call(path, [arg]) => {
+        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()
-            {
-                (cx.typeck_results().expr_ty(arg), snippet(cx, arg.span, ".."))
-            } else {
-                return;
-            }
+                .is_some() =>
+        {
+            (arg, arg.span)
         },
         _ => return,
     };
 
-    let other_ty = cx.typeck_results().expr_ty(other);
+    let arg_ty = typeck.expr_ty(arg);
+    let other_ty = typeck.expr_ty(other);
 
     let without_deref = symmetric_partial_eq(cx, arg_ty, other_ty).unwrap_or_default();
     let with_deref = arg_ty
@@ -627,13 +624,14 @@ fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left:
                 return;
             }
 
+            let arg_snip = snippet(cx, arg_span, "..");
             let expr_snip;
             let eq_impl;
             if with_deref.is_implemented() {
-                expr_snip = format!("*{}", snip);
+                expr_snip = format!("*{}", arg_snip);
                 eq_impl = with_deref;
             } else {
-                expr_snip = snip.to_string();
+                expr_snip = arg_snip.to_string();
                 eq_impl = without_deref;
             };