Add should_call_clone_as_function() utility function

Author: samueltardieu

clippy_lints/src/methods/map_clone.rs

@@ -1,7 +1,7 @@
 use clippy_config::msrvs::{self, Msrv};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
-use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
+use clippy_utils::ty::{is_copy, is_type_diagnostic_item, should_call_clone_as_function};
 use clippy_utils::{is_diag_trait_item, match_def_path, paths, peel_blocks};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -124,11 +124,7 @@ fn handle_path(
             && let ty::Ref(_, ty, Mutability::Not) = ty.kind()
             && let ty::FnDef(_, lst) = cx.typeck_results().expr_ty(arg).kind()
             && lst.iter().all(|l| l.as_type() == Some(*ty))
-            && !matches!(
-                ty.ty_adt_def()
-                    .and_then(|adt_def| cx.tcx.get_diagnostic_name(adt_def.did())),
-                Some(sym::Arc | sym::ArcWeak | sym::Rc | sym::RcWeak)
-            )
+            && !should_call_clone_as_function(cx, *ty)
         {
             lint_path(cx, e.span, recv.span, is_copy(cx, ty.peel_refs()));
         }

clippy_utils/src/ty.rs

@@ -159,6 +159,16 @@ pub fn get_type_diagnostic_name(cx: &LateContext<'_>, ty: Ty<'_>) -> Option<Symb
     }
 }
 
+/// Returns true if `ty` is a type on which calling `Clone` through a function instead of
+/// as a method, such as `Arc::clone()` is considered idiomatic. Lints should avoid suggesting to
+/// replace instances of `ty::Clone()` by `.clone()` for objects of those types.
+pub fn should_call_clone_as_function(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
+    matches!(
+        get_type_diagnostic_name(cx, ty),
+        Some(sym::Arc | sym::ArcWeak | sym::Rc | sym::RcWeak)
+    )
+}
+
 /// Returns true if ty has `iter` or `iter_mut` methods
 pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
     // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`