Fix E0040 suggestion for explicit Drop::drop UFCS calls

`Drop::drop(&mut f)` now correctly suggests `drop(f)` instead of
the bare `drop` with no argument.

Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

Author: Unique-Usman

compiler/rustc_hir_typeck/src/callee.rs

@@ -42,7 +42,7 @@ pub(crate) fn check_legal_trait_for_method_call(
     if tcx.is_lang_item(trait_id, LangItem::Drop) {
         let sugg = if let Some(receiver) = receiver.filter(|s| !s.is_empty()) {
             errors::ExplicitDestructorCallSugg::Snippet {
-                lo: expr_span.shrink_to_lo(),
+                lo: expr_span.shrink_to_lo().to(receiver.shrink_to_lo()),
                 hi: receiver.shrink_to_hi().to(expr_span.shrink_to_hi()),
             }
         } else {

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1013,10 +1013,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 debug!(?def_id, ?container, ?container_id);
                 match container {
                     ty::AssocContainer::Trait => {
+                        let arg_span = if let hir::Node::Expr(call_expr) =
+                            self.tcx.parent_hir_node(hir_id)
+                            && let hir::ExprKind::Call(_, args) = call_expr.kind
+                            && let Some(first_arg) = args.first()
+                        {
+                            let mut arg = first_arg;
+                            while let hir::ExprKind::AddrOf(_, _, inner) = arg.kind {
+                                arg = inner;
+                            }
+                            Some(arg.span)
+                        } else {
+                            None
+                        };
+
                         if let Err(e) = callee::check_legal_trait_for_method_call(
                             tcx,
                             path_span,
-                            None,
+                            arg_span,
                             span,
                             container_id,
                             self.body_id.to_def_id(),

compiler/rustc_lint/src/lib.rs

@@ -88,6 +88,7 @@ use dangling::*;
 use default_could_be_derived::DefaultCouldBeDerived;
 use deref_into_dyn_supertrait::*;
 use disallowed_pass_by_ref::*;
+pub use drop_forget_useless::DROPPING_REFERENCES;
 use drop_forget_useless::*;
 use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
 use for_loops_over_fallibles::*;

tests/ui/drop/explicit-drop-call-error.fixed

@@ -11,5 +11,5 @@ impl Drop for Foo {
 }
 
 fn main() {
-    drop(&mut Foo) //~ ERROR explicit use of destructor method
+    drop(Foo) //~ ERROR explicit use of destructor method
 }

tests/ui/drop/explicit-drop-call-error.stderr

@@ -2,10 +2,13 @@ error[E0040]: explicit use of destructor method
   --> $DIR/explicit-drop-call-error.rs:14:5
    |
 LL |     Drop::drop(&mut Foo)
-   |     ^^^^^^^^^^
-   |     |
-   |     explicit destructor calls not allowed
-   |     help: consider using `drop` function: `drop`
+   |     ^^^^^^^^^^ explicit destructor calls not allowed
+   |
+help: consider using `drop` function
+   |
+LL -     Drop::drop(&mut Foo)
+LL +     drop(Foo)
+   |
 
 error: aborting due to 1 previous error
 

tests/ui/drop/explicit-drop-call-named-ref.fixed

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+struct Foo;
+
+impl Drop for Foo {
+    fn drop(&mut self) {}
+}
+
+fn foo(f: Foo) {
+    drop(f); //~ ERROR explicit use of destructor method
+    //~| HELP: consider using `drop` function
+}
+
+fn main() {
+    let f = Foo;
+    foo(f);
+}

tests/ui/drop/explicit-drop-call-named-ref.rs

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+struct Foo;
+
+impl Drop for Foo {
+    fn drop(&mut self) {}
+}
+
+fn foo(f: Foo) {
+    Drop::drop(&mut f); //~ ERROR explicit use of destructor method
+    //~| HELP: consider using `drop` function
+}
+
+fn main() {
+    let f = Foo;
+    foo(f);
+}

tests/ui/drop/explicit-drop-call-named-ref.stderr

@@ -0,0 +1,15 @@
+error[E0040]: explicit use of destructor method
+  --> $DIR/explicit-drop-call-named-ref.rs:10:5
+   |
+LL |     Drop::drop(&mut f);
+   |     ^^^^^^^^^^ explicit destructor calls not allowed
+   |
+help: consider using `drop` function
+   |
+LL -     Drop::drop(&mut f);
+LL +     drop(f);
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0040`.