From 10649002de3789f93a4cb1647d9adf446f02ccab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matthias=20Kr=C3=BCger?= <matthias.krueger@famsik.de>
Date: Tue, 11 Aug 2020 12:35:55 +0200
Subject: [PATCH] unnecessary-mut-passed: make lint message say if fn is a
 function or a method.

---
 clippy_lints/src/mut_reference.rs | 15 ++++++++++++---
 tests/ui/mut_reference.stderr     |  6 +++---
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/clippy_lints/src/mut_reference.rs b/clippy_lints/src/mut_reference.rs
index b8dc50816329..c3ad7258158a 100644
--- a/clippy_lints/src/mut_reference.rs
+++ b/clippy_lints/src/mut_reference.rs
@@ -39,6 +39,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryMutPassed {
                         arguments,
                         cx.typeck_results().expr_ty(fn_expr),
                         &rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_qpath(path, false)),
+                        false,
                     );
                 }
             },
@@ -46,14 +47,22 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryMutPassed {
                 let def_id = cx.typeck_results().type_dependent_def_id(e.hir_id).unwrap();
                 let substs = cx.typeck_results().node_substs(e.hir_id);
                 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
-                check_arguments(cx, arguments, method_type, &path.ident.as_str())
+                check_arguments(cx, arguments, method_type, &path.ident.as_str(), true)
             },
             _ => (),
         }
     }
 }
 
-fn check_arguments<'tcx>(cx: &LateContext<'tcx>, arguments: &[Expr<'_>], type_definition: Ty<'tcx>, name: &str) {
+fn check_arguments<'tcx>(
+    cx: &LateContext<'tcx>,
+    arguments: &[Expr<'_>],
+    type_definition: Ty<'tcx>,
+    name: &str,
+    method_call: bool,
+) {
+    let fn_kind: &str = if method_call { "method" } else { "function" };
+
     match type_definition.kind {
         ty::FnDef(..) | ty::FnPtr(_) => {
             let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
@@ -68,7 +77,7 @@ fn check_arguments<'tcx>(cx: &LateContext<'tcx>, arguments: &[Expr<'_>], type_de
                                 cx,
                                 UNNECESSARY_MUT_PASSED,
                                 argument.span,
-                                &format!("The function/method `{}` doesn't need a mutable reference", name),
+                                &format!("the {} `{}` doesn't need a mutable reference", fn_kind, name),
                             );
                         }
                     },
diff --git a/tests/ui/mut_reference.stderr b/tests/ui/mut_reference.stderr
index fa8c82ae0f34..062d30b262c1 100644
--- a/tests/ui/mut_reference.stderr
+++ b/tests/ui/mut_reference.stderr
@@ -1,4 +1,4 @@
-error: The function/method `takes_an_immutable_reference` doesn't need a mutable reference
+error: the function `takes_an_immutable_reference` doesn't need a mutable reference
   --> $DIR/mut_reference.rs:17:34
    |
 LL |     takes_an_immutable_reference(&mut 42);
@@ -6,13 +6,13 @@ LL |     takes_an_immutable_reference(&mut 42);
    |
    = note: `-D clippy::unnecessary-mut-passed` implied by `-D warnings`
 
-error: The function/method `as_ptr` doesn't need a mutable reference
+error: the function `as_ptr` doesn't need a mutable reference
   --> $DIR/mut_reference.rs:19:12
    |
 LL |     as_ptr(&mut 42);
    |            ^^^^^^^
 
-error: The function/method `takes_an_immutable_reference` doesn't need a mutable reference
+error: the method `takes_an_immutable_reference` doesn't need a mutable reference
   --> $DIR/mut_reference.rs:23:44
    |
 LL |     my_struct.takes_an_immutable_reference(&mut 42);