fix(should_implement_trait): only suggest traits that are in the prelude (#15776)

Fixes #6752

changelog: [should_implement_trait]: only suggest traits that are in the
prelude

Author: samueltardieu

clippy_lints/src/methods/lib.rs

@@ -0,0 +1,70 @@
+use clippy_utils::sym;
+use clippy_utils::ty::{implements_trait, is_copy};
+use rustc_hir::Mutability;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub(super) enum SelfKind {
+    Value,
+    Ref,
+    RefMut,
+    No, // When we want the first argument type to be different than `Self`
+}
+
+impl SelfKind {
+    pub(super) fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
+        fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
+            if ty == parent_ty {
+                true
+            } else if let Some(boxed_ty) = ty.boxed_ty() {
+                boxed_ty == parent_ty
+            } else if let ty::Adt(adt_def, args) = ty.kind()
+                && matches!(cx.tcx.get_diagnostic_name(adt_def.did()), Some(sym::Rc | sym::Arc))
+            {
+                args.types().next() == Some(parent_ty)
+            } else {
+                false
+            }
+        }
+
+        fn matches_ref<'a>(cx: &LateContext<'a>, mutability: Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
+            if let ty::Ref(_, t, m) = *ty.kind() {
+                return m == mutability && t == parent_ty;
+            }
+
+            let trait_sym = match mutability {
+                Mutability::Not => sym::AsRef,
+                Mutability::Mut => sym::AsMut,
+            };
+
+            let Some(trait_def_id) = cx.tcx.get_diagnostic_item(trait_sym) else {
+                return false;
+            };
+            implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
+        }
+
+        fn matches_none<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
+            !matches_value(cx, parent_ty, ty)
+                && !matches_ref(cx, Mutability::Not, parent_ty, ty)
+                && !matches_ref(cx, Mutability::Mut, parent_ty, ty)
+        }
+
+        match self {
+            Self::Value => matches_value(cx, parent_ty, ty),
+            Self::Ref => matches_ref(cx, Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
+            Self::RefMut => matches_ref(cx, Mutability::Mut, parent_ty, ty),
+            Self::No => matches_none(cx, parent_ty, ty),
+        }
+    }
+
+    #[must_use]
+    pub(super) fn description(self) -> &'static str {
+        match self {
+            Self::Value => "`self` by value",
+            Self::Ref => "`self` by reference",
+            Self::RefMut => "`self` by mutable reference",
+            Self::No => "no `self`",
+        }
+    }
+}