Allow Self::cmp(self, other) as a correct impl

Author: Centri3

clippy_lints/src/incorrect_impls.rs

@@ -1,8 +1,9 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
+use clippy_utils::paths::ORD_CMP;
 use clippy_utils::ty::implements_trait;
-use clippy_utils::{get_parent_node, is_res_lang_ctor, last_path_segment, path_res};
+use clippy_utils::{get_parent_node, is_res_lang_ctor, last_path_segment, match_def_path, path_res};
 use rustc_errors::Applicability;
-use rustc_hir::def::Res;
+use rustc_hir::def_id::LocalDefId;
 use rustc_hir::{Expr, ExprKind, ImplItem, ImplItemKind, ItemKind, LangItem, Node, UnOp};
 use rustc_hir_analysis::hir_ty_to_ty;
 use rustc_lint::{LateContext, LateLintPass};
@@ -19,6 +20,10 @@ declare_clippy_lint! {
     /// If both `Clone` and `Copy` are implemented, they must agree. This is done by dereferencing
     /// `self` in `Clone`'s implementation. Anything else is incorrect.
     ///
+    /// ### Known issues
+    /// Code like `self.cmp(other).into()` will be flagged as incorrect, despite `.into()` wrapping
+    /// it in `Some`.
+    ///
     /// ### Example
     /// ```rust,ignore
     /// #[derive(Eq, PartialEq)]
@@ -202,9 +207,8 @@ impl LateLintPass<'_> for IncorrectImpls {
                         [cmp_expr],
                     ) = expr.kind
                 && is_res_lang_ctor(cx, cx.qpath_res(some_path, *some_hir_id), LangItem::OptionSome)
-                && let ExprKind::MethodCall(cmp_path, _, [other_expr], ..) = cmp_expr.kind
-                && cmp_path.ident.name == sym::cmp
-                && let Res::Local(..) = path_res(cx, other_expr)
+                // Fix #11178, allow `Self::cmp(self, ..)` too
+                && self_cmp_call(cx, cmp_expr, impl_item.owner_id.def_id)
             {} else {
                 // If `Self` and `Rhs` are not the same type, bail. This makes creating a valid
                 // suggestion tons more complex.
@@ -242,3 +246,21 @@ impl LateLintPass<'_> for IncorrectImpls {
         }
     }
 }
+
+/// Returns whether this is `self.cmp(..)`, `Self::cmp(self, ..)` or `Ord::cmp(self, ..)`.
+fn self_cmp_call<'tcx>(cx: &LateContext<'tcx>, cmp_expr: &'tcx Expr<'tcx>, def_id: LocalDefId) -> bool {
+    match cmp_expr.kind {
+        ExprKind::Call(path, [_self, _other]) => path_res(cx, path)
+            .opt_def_id()
+            .is_some_and(|def_id| match_def_path(cx, def_id, &ORD_CMP)),
+        ExprKind::MethodCall(_, _, [_other], ..) => {
+            // It's a bit annoying but `typeck_results` only gives us the CURRENT body, which we have none, not
+            // of any `LocalDefId` we want, so we must call the query itself to avoid an immediate ICE
+            cx.tcx
+                .typeck(def_id)
+                .type_dependent_def_id(cmp_expr.hir_id)
+                .is_some_and(|def_id| match_def_path(cx, def_id, &ORD_CMP))
+        },
+        _ => false,
+    }
+}

clippy_utils/src/paths.rs

@@ -161,3 +161,4 @@ pub const OPTION_UNWRAP: [&str; 4] = ["core", "option", "Option", "unwrap"];
 pub const OPTION_EXPECT: [&str; 4] = ["core", "option", "Option", "expect"];
 pub const FORMATTER: [&str; 3] = ["core", "fmt", "Formatter"];
 pub const DEBUG_STRUCT: [&str; 4] = ["core", "fmt", "builders", "DebugStruct"];
+pub const ORD_CMP: [&str; 4] = ["core", "cmp", "Ord", "cmp"];

tests/ui/incorrect_partial_ord_impl_on_ord_type.fixed

@@ -112,3 +112,35 @@ impl PartialOrd<u32> for F {
         todo!();
     }
 }
+
+// #11178, do not lint
+
+#[derive(Eq, PartialEq)]
+struct G(u32);
+
+impl Ord for G {
+    fn cmp(&self, other: &Self) -> Ordering {
+        todo!();
+    }
+}
+
+impl PartialOrd for G {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(Self::cmp(self, other))
+    }
+}
+
+#[derive(Eq, PartialEq)]
+struct H(u32);
+
+impl Ord for H {
+    fn cmp(&self, other: &Self) -> Ordering {
+        todo!();
+    }
+}
+
+impl PartialOrd for H {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(Ord::cmp(self, other))
+    }
+}

tests/ui/incorrect_partial_ord_impl_on_ord_type.rs

@@ -116,3 +116,35 @@ impl PartialOrd<u32> for F {
         todo!();
     }
 }
+
+// #11178, do not lint
+
+#[derive(Eq, PartialEq)]
+struct G(u32);
+
+impl Ord for G {
+    fn cmp(&self, other: &Self) -> Ordering {
+        todo!();
+    }
+}
+
+impl PartialOrd for G {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(Self::cmp(self, other))
+    }
+}
+
+#[derive(Eq, PartialEq)]
+struct H(u32);
+
+impl Ord for H {
+    fn cmp(&self, other: &Self) -> Ordering {
+        todo!();
+    }
+}
+
+impl PartialOrd for H {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(Ord::cmp(self, other))
+    }
+}