only run flop lints on inherent method calls

clippy_lints/src/floating_point_arithmetic.rs

@@ -2,7 +2,8 @@
 use clippy_utils::consts::{constant, constant_simple, Constant};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::{
-    eq_expr_value, get_parent_expr, higher, in_constant, is_no_std_crate, numeric_literal, peel_blocks, sugg,
+    eq_expr_value, get_parent_expr, higher, in_constant, is_inherent_method_call, is_no_std_crate, numeric_literal,
+    peel_blocks, sugg,
 };
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
@@ -759,7 +760,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::MethodCall(path, receiver, args, _) = &expr.kind {
             let recv_ty = cx.typeck_results().expr_ty(receiver);
 
-            if recv_ty.is_floating_point() && !is_no_std_crate(cx) {
+            if recv_ty.is_floating_point() && !is_no_std_crate(cx) && is_inherent_method_call(cx, expr) {
                 match path.ident.name.as_str() {
                     "ln" => check_ln1p(cx, expr, receiver),
                     "log" => check_log_base(cx, expr, receiver, args),

clippy_utils/src/lib.rs

@@ -321,6 +321,15 @@ pub fn match_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, path: &[&str])
         .map_or(false, |trt_id| match_def_path(cx, trt_id, path))
 }
 
+/// Checks if the given method call expression calls an inherent method.
+pub fn is_inherent_method_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
+        cx.tcx.trait_of_item(method_id).is_none()
+    } else {
+        false
+    }
+}
+
 /// Checks if a method is defined in an impl of a diagnostic item
 pub fn is_diag_item_method(cx: &LateContext<'_>, def_id: DefId, diag_item: Symbol) -> bool {
     if let Some(impl_did) = cx.tcx.impl_of_method(def_id) {

tests/ui/floating_point_log.fixed

@@ -55,4 +55,19 @@ fn check_ln1p() {
     let _ = (1.0 + x - 2.0).ln();
 }
 
+fn issue12881() {
+    pub trait MyLog {
+        fn log(&self) -> Self;
+    }
+
+    impl MyLog for f32 {
+        fn log(&self) -> Self {
+            4.
+        }
+    }
+
+    let x = 2.0;
+    x.log();
+}
+
 fn main() {}

tests/ui/floating_point_log.rs

@@ -55,4 +55,19 @@ fn check_ln1p() {
     let _ = (1.0 + x - 2.0).ln();
 }
 
+fn issue12881() {
+    pub trait MyLog {
+        fn log(&self) -> Self;
+    }
+
+    impl MyLog for f32 {
+        fn log(&self) -> Self {
+            4.
+        }
+    }
+
+    let x = 2.0;
+    x.log();
+}
+
 fn main() {}