Change from correctness to style and MaybeIncorrect instead of MachineApplicable

clippy_lints/src/lib.rs

@@ -1621,6 +1621,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&misc_early::DUPLICATE_UNDERSCORE_ARGUMENT),
         LintId::of(&misc_early::MIXED_CASE_HEX_LITERALS),
         LintId::of(&misc_early::REDUNDANT_PATTERN),
+        LintId::of(&mut_mutex_lock::MUT_MUTEX_LOCK),
         LintId::of(&mut_reference::UNNECESSARY_MUT_PASSED),
         LintId::of(&neg_multiply::NEG_MULTIPLY),
         LintId::of(&new_without_default::NEW_WITHOUT_DEFAULT),
@@ -1784,7 +1785,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&misc::FLOAT_CMP),
         LintId::of(&misc::MODULO_ONE),
         LintId::of(&mut_key::MUTABLE_KEY_TYPE),
-        LintId::of(&mut_mutex_lock::MUT_MUTEX_LOCK),
         LintId::of(&open_options::NONSENSICAL_OPEN_OPTIONS),
         LintId::of(&option_env_unwrap::OPTION_ENV_UNWRAP),
         LintId::of(&ptr::MUT_FROM_REF),

clippy_lints/src/mut_mutex_lock.rs

@@ -38,7 +38,7 @@
     /// *value += 1;
     /// ```
     pub MUT_MUTEX_LOCK,
-    correctness,
+    style,
     "`&mut Mutex::lock` does unnecessary locking"
 }
 
@@ -60,7 +60,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, ex: &'tcx Expr<'tcx>) {
                     "calling `&mut Mutex::lock` unnecessarily locks an exclusive (mutable) reference",
                     "change this to",
                     "get_mut".to_owned(),
-                    Applicability::MachineApplicable,
+                    Applicability::MaybeIncorrect,
                 );
             }
         }

src/lintlist/mod.rs

@@ -1504,7 +1504,7 @@
     },
     Lint {
         name: "mut_mutex_lock",
-        group: "correctness",
+        group: "style",
         desc: "`&mut Mutex::lock` does unnecessary locking",
         deprecation: None,
         module: "mut_mutex_lock",