Fix `assign_op_pattern` FP on unstable const trait (#14886)

Closes rust-lang/rust-clippy#14871

----

changelog: [`assign_op_pattern`]: fix false positive on unstable const
trait

2 files changed, 14 insertions, 2 deletions

diff --git a/clippy_lints/src/operators/assign_op_pattern.rs b/clippy_lints/src/operators/assign_op_pattern.rs
index 4be42267b14..9c6141d8222 100644
--- a/clippy_lints/src/operators/assign_op_pattern.rs
+++ b/clippy_lints/src/operators/assign_op_pattern.rs
@@ -1,8 +1,10 @@
 use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::msrvs::Msrv;
+use clippy_utils::qualify_min_const_fn::is_stable_const_fn;
 use clippy_utils::source::SpanRangeExt;
 use clippy_utils::ty::implements_trait;
 use clippy_utils::visitors::for_each_expr_without_closures;
-use clippy_utils::{binop_traits, eq_expr_value, trait_ref_of_method};
+use clippy_utils::{binop_traits, eq_expr_value, is_in_const_context, trait_ref_of_method};
 use core::ops::ControlFlow;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -19,6 +21,7 @@ pub(super) fn check<'tcx>(
     expr: &'tcx hir::Expr<'_>,
     assignee: &'tcx hir::Expr<'_>,
     e: &'tcx hir::Expr<'_>,
+    msrv: Msrv,
 ) {
     if let hir::ExprKind::Binary(op, l, r) = &e.kind {
         let lint = |assignee: &hir::Expr<'_>, rhs: &hir::Expr<'_>| {
@@ -40,6 +43,15 @@ pub(super) fn check<'tcx>(
                         return;
                     }
                 }
+
+                // Skip if the trait is not stable in const contexts
+                if is_in_const_context(cx)
+                    && let Some(binop_id) = cx.tcx.associated_item_def_ids(trait_id).first()
+                    && !is_stable_const_fn(cx, *binop_id, msrv)
+                {
+                    return;
+                }
+
                 span_lint_and_then(
                     cx,
                     ASSIGN_OP_PATTERN,
diff --git a/clippy_lints/src/operators/mod.rs b/clippy_lints/src/operators/mod.rs
index d32c062cf56..2f4e8e99588 100644
--- a/clippy_lints/src/operators/mod.rs
+++ b/clippy_lints/src/operators/mod.rs
@@ -919,7 +919,7 @@ impl<'tcx> LateLintPass<'tcx> for Operators {
                 modulo_arithmetic::check(cx, e, bin_op, lhs, rhs, false);
             },
             ExprKind::Assign(lhs, rhs, _) => {
-                assign_op_pattern::check(cx, e, lhs, rhs);
+                assign_op_pattern::check(cx, e, lhs, rhs, self.msrv);
                 self_assignment::check(cx, e, lhs, rhs);
             },
             ExprKind::Unary(op, arg) => {