Fix assign_op_pattern FP on unstable const trait

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,

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) => {

clippy_utils/src/qualify_min_const_fn.rs

@@ -393,7 +393,8 @@ fn check_terminator<'tcx>(
     }
 }
 
-fn is_stable_const_fn(cx: &LateContext<'_>, def_id: DefId, msrv: Msrv) -> bool {
+/// Checks if the given `def_id` is a stable const fn, in respect to the given MSRV.
+pub fn is_stable_const_fn(cx: &LateContext<'_>, def_id: DefId, msrv: Msrv) -> bool {
     cx.tcx.is_const_fn(def_id)
         && cx
             .tcx

tests/ui/assign_ops.fixed

@@ -1,5 +1,6 @@
 #![allow(clippy::useless_vec)]
 #![warn(clippy::assign_op_pattern)]
+#![feature(const_trait_impl, const_ops)]
 
 use core::num::Wrapping;
 use std::ops::{Mul, MulAssign};
@@ -73,3 +74,33 @@ impl MulAssign<i64> for Wrap {
         *self = *self * rhs
     }
 }
+
+mod issue14871 {
+
+    use std::ops::{Add, AddAssign};
+
+    pub trait Number: Copy + Add<Self, Output = Self> + AddAssign {
+        const ZERO: Self;
+        const ONE: Self;
+    }
+
+    #[const_trait]
+    pub trait NumberConstants {
+        fn constant(value: usize) -> Self;
+    }
+
+    impl<T> const NumberConstants for T
+    where
+        T: Number + ~const core::ops::Add,
+    {
+        fn constant(value: usize) -> Self {
+            let mut res = Self::ZERO;
+            let mut count = 0;
+            while count < value {
+                res = res + Self::ONE;
+                count += 1;
+            }
+            res
+        }
+    }
+}

tests/ui/assign_ops.rs

@@ -1,5 +1,6 @@
 #![allow(clippy::useless_vec)]
 #![warn(clippy::assign_op_pattern)]
+#![feature(const_trait_impl, const_ops)]
 
 use core::num::Wrapping;
 use std::ops::{Mul, MulAssign};
@@ -73,3 +74,33 @@ impl MulAssign<i64> for Wrap {
         *self = *self * rhs
     }
 }
+
+mod issue14871 {
+
+    use std::ops::{Add, AddAssign};
+
+    pub trait Number: Copy + Add<Self, Output = Self> + AddAssign {
+        const ZERO: Self;
+        const ONE: Self;
+    }
+
+    #[const_trait]
+    pub trait NumberConstants {
+        fn constant(value: usize) -> Self;
+    }
+
+    impl<T> const NumberConstants for T
+    where
+        T: Number + ~const core::ops::Add,
+    {
+        fn constant(value: usize) -> Self {
+            let mut res = Self::ZERO;
+            let mut count = 0;
+            while count < value {
+                res = res + Self::ONE;
+                count += 1;
+            }
+            res
+        }
+    }
+}

tests/ui/assign_ops.stderr

@@ -1,5 +1,5 @@
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:9:5
+  --> tests/ui/assign_ops.rs:10:5
    |
 LL |     a = a + 1;
    |     ^^^^^^^^^ help: replace it with: `a += 1`
@@ -8,67 +8,67 @@ LL |     a = a + 1;
    = help: to override `-D warnings` add `#[allow(clippy::assign_op_pattern)]`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:11:5
+  --> tests/ui/assign_ops.rs:12:5
    |
 LL |     a = 1 + a;
    |     ^^^^^^^^^ help: replace it with: `a += 1`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:13:5
+  --> tests/ui/assign_ops.rs:14:5
    |
 LL |     a = a - 1;
    |     ^^^^^^^^^ help: replace it with: `a -= 1`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:15:5
+  --> tests/ui/assign_ops.rs:16:5
    |
 LL |     a = a * 99;
    |     ^^^^^^^^^^ help: replace it with: `a *= 99`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:17:5
+  --> tests/ui/assign_ops.rs:18:5
    |
 LL |     a = 42 * a;
    |     ^^^^^^^^^^ help: replace it with: `a *= 42`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:19:5
+  --> tests/ui/assign_ops.rs:20:5
    |
 LL |     a = a / 2;
    |     ^^^^^^^^^ help: replace it with: `a /= 2`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:21:5
+  --> tests/ui/assign_ops.rs:22:5
    |
 LL |     a = a % 5;
    |     ^^^^^^^^^ help: replace it with: `a %= 5`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:23:5
+  --> tests/ui/assign_ops.rs:24:5
    |
 LL |     a = a & 1;
    |     ^^^^^^^^^ help: replace it with: `a &= 1`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:30:5
+  --> tests/ui/assign_ops.rs:31:5
    |
 LL |     s = s + "bla";
    |     ^^^^^^^^^^^^^ help: replace it with: `s += "bla"`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:35:5
+  --> tests/ui/assign_ops.rs:36:5
    |
 LL |     a = a + Wrapping(1u32);
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `a += Wrapping(1u32)`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:38:5
+  --> tests/ui/assign_ops.rs:39:5
    |
 LL |     v[0] = v[0] + v[1];
    |     ^^^^^^^^^^^^^^^^^^ help: replace it with: `v[0] += v[1]`
 
 error: manual implementation of an assign operation
-  --> tests/ui/assign_ops.rs:51:5
+  --> tests/ui/assign_ops.rs:52:5
    |
 LL |     buf = buf + cows.clone();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `buf += cows.clone()`