Auto merge of #12442 - cookie-s:fix-mutmut-duplicate-diags, r=y21

[`mut_mut`]: Fix duplicate diags

Relates to #12379

The `mut_mut` lint produced two diagnostics for each `mut mut` pattern in `ty` inside  `block`s because `MutVisitor::visit_ty` was called from `MutMut::check_ty` and  `MutMut::check_block` independently. This PR fixes the issue.

---

changelog: [`mut_mut`]: Fix duplicate diagnostics

Author: bors

Diff for: clippy_lints/src/mut_mut.rs

@@ -35,9 +35,34 @@ impl<'tcx> LateLintPass<'tcx> for MutMut {
     }
 
     fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>) {
-        use rustc_hir::intravisit::Visitor;
+        if in_external_macro(cx.sess(), ty.span) {
+            return;
+        }
 
-        MutVisitor { cx }.visit_ty(ty);
+        if let hir::TyKind::Ref(
+            _,
+            hir::MutTy {
+                ty: pty,
+                mutbl: hir::Mutability::Mut,
+            },
+        ) = ty.kind
+        {
+            if let hir::TyKind::Ref(
+                _,
+                hir::MutTy {
+                    mutbl: hir::Mutability::Mut,
+                    ..
+                },
+            ) = pty.kind
+            {
+                span_lint(
+                    cx,
+                    MUT_MUT,
+                    ty.span,
+                    "generally you want to avoid `&mut &mut _` if possible",
+                );
+            }
+        }
     }
 }
 
@@ -80,37 +105,4 @@ impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
             }
         }
     }
-
-    fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
-        if in_external_macro(self.cx.sess(), ty.span) {
-            return;
-        }
-
-        if let hir::TyKind::Ref(
-            _,
-            hir::MutTy {
-                ty: pty,
-                mutbl: hir::Mutability::Mut,
-            },
-        ) = ty.kind
-        {
-            if let hir::TyKind::Ref(
-                _,
-                hir::MutTy {
-                    mutbl: hir::Mutability::Mut,
-                    ..
-                },
-            ) = pty.kind
-            {
-                span_lint(
-                    self.cx,
-                    MUT_MUT,
-                    ty.span,
-                    "generally you want to avoid `&mut &mut _` if possible",
-                );
-            }
-        }
-
-        intravisit::walk_ty(self, ty);
-    }
 }

Diff for: tests/ui/mut_mut.rs

@@ -1,5 +1,4 @@
 //@aux-build:proc_macros.rs
-//@compile-flags: -Zdeduplicate-diagnostics=yes
 
 #![warn(clippy::mut_mut)]
 #![allow(unused)]

Diff for: tests/ui/mut_mut.stderr

@@ -1,5 +1,5 @@
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:16:11
+  --> tests/ui/mut_mut.rs:15:11
    |
 LL | fn fun(x: &mut &mut u32) -> bool {
    |           ^^^^^^^^^^^^^
@@ -8,51 +8,51 @@ LL | fn fun(x: &mut &mut u32) -> bool {
    = help: to override `-D warnings` add `#[allow(clippy::mut_mut)]`
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:33:17
+  --> tests/ui/mut_mut.rs:32:17
    |
 LL |     let mut x = &mut &mut 1u32;
    |                 ^^^^^^^^^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:48:25
+  --> tests/ui/mut_mut.rs:47:25
    |
 LL |     let mut z = inline!(&mut $(&mut 3u32));
    |                         ^
    |
    = note: this error originates in the macro `__inline_mac_fn_main` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: this expression mutably borrows a mutable reference. Consider reborrowing
-  --> tests/ui/mut_mut.rs:35:21
+  --> tests/ui/mut_mut.rs:34:21
    |
 LL |         let mut y = &mut x;
    |                     ^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:39:32
+  --> tests/ui/mut_mut.rs:38:32
    |
 LL |         let y: &mut &mut u32 = &mut &mut 2;
    |                                ^^^^^^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:39:16
+  --> tests/ui/mut_mut.rs:38:16
    |
 LL |         let y: &mut &mut u32 = &mut &mut 2;
    |                ^^^^^^^^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:44:37
+  --> tests/ui/mut_mut.rs:43:37
    |
 LL |         let y: &mut &mut &mut u32 = &mut &mut &mut 2;
    |                                     ^^^^^^^^^^^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:44:16
+  --> tests/ui/mut_mut.rs:43:16
    |
 LL |         let y: &mut &mut &mut u32 = &mut &mut &mut 2;
    |                ^^^^^^^^^^^^^^^^^^
 
 error: generally you want to avoid `&mut &mut _` if possible
-  --> tests/ui/mut_mut.rs:44:21
+  --> tests/ui/mut_mut.rs:43:21
    |
 LL |         let y: &mut &mut &mut u32 = &mut &mut &mut 2;
    |                     ^^^^^^^^^^^^^