Improve warning

Author: rylev

compiler/rustc_lint/src/noop_method_call.rs

@@ -70,11 +70,13 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
                             .iter()
                             .any(|s| cx.tcx.is_diagnostic_item(*s, i.def_id()))
                             {
-                                let span = expr.span;
+                                let expr_span = expr.span;
 
-                                cx.struct_span_lint(NOOP_METHOD_CALL, span, |lint| {
-                                    let message = "call to noop method";
-                                    lint.build(&message).emit()
+                                cx.struct_span_lint(NOOP_METHOD_CALL, expr_span, |lint| {
+                                    let message = "call to method that does nothing";
+                                    lint.build(&message)
+                                        .span_label(expr_span, "unnecessary method call")
+                                        .emit()
                                 });
                             }
                         }

src/test/ui/lint/noop-method-call.rs

@@ -21,25 +21,25 @@ impl<T> Deref for DerefExample<T> {
 
 fn main() {
     let foo = &Foo(1u32);
-    let foo_clone: &Foo<u32> = foo.clone(); //~ WARNING call to noop method
+    let foo_clone: &Foo<u32> = foo.clone(); //~ WARNING call to method that does nothing [noop_method_call]
 
     let bar = &Bar(1u32);
     let bar_clone: Bar<u32> = bar.clone();
 
     let deref = &&DerefExample(12u32);
-    let derefed: &DerefExample<u32> = deref.deref(); //~ WARNING call to noop method
+    let derefed: &DerefExample<u32> = deref.deref(); //~ WARNING call to method that does nothing [noop_method_call]
 
     let deref = &DerefExample(12u32);
     let derefed: &u32 = deref.deref();
 
     let a = &&Foo(1u32);
-    let borrowed: &Foo<u32> = a.borrow(); //~ WARNING call to noop method
+    let borrowed: &Foo<u32> = a.borrow(); //~ WARNING call to method that does nothing [noop_method_call]
 }
 
 fn generic<T>(foo: &Foo<T>) {
     foo.clone();
 }
 
 fn non_generic(foo: &Foo<u32>) {
-    foo.clone(); //~ WARNING call to noop method
+    foo.clone(); //~ WARNING call to method that does nothing [noop_method_call]
 }

src/test/ui/lint/noop-method-call.stderr

@@ -1,28 +1,28 @@
-warning: call to noop method
+warning: call to method that does nothing
   --> $DIR/noop-method-call.rs:24:32
    |
 LL |     let foo_clone: &Foo<u32> = foo.clone();
-   |                                ^^^^^^^^^^^
+   |                                ^^^^^^^^^^^ unnecessary method call
    |
    = note: `#[warn(noop_method_call)]` on by default
 
-warning: call to noop method
+warning: call to method that does nothing
   --> $DIR/noop-method-call.rs:30:39
    |
 LL |     let derefed: &DerefExample<u32> = deref.deref();
-   |                                       ^^^^^^^^^^^^^
+   |                                       ^^^^^^^^^^^^^ unnecessary method call
 
-warning: call to noop method
+warning: call to method that does nothing
   --> $DIR/noop-method-call.rs:36:31
    |
 LL |     let borrowed: &Foo<u32> = a.borrow();
-   |                               ^^^^^^^^^^
+   |                               ^^^^^^^^^^ unnecessary method call
 
-warning: call to noop method
+warning: call to method that does nothing
   --> $DIR/noop-method-call.rs:44:5
    |
 LL |     foo.clone();
-   |     ^^^^^^^^^^^
+   |     ^^^^^^^^^^^ unnecessary method call
 
 warning: 4 warnings emitted