Do not trigger if_let_mutex starting from Edition 2024 (#13695)

Close #13679

changelog: [`if_let_mutex`]: disable lint from Edition 2024 since
[stabilized if_let_rescope
](https://github.com/rust-lang/rust/issues/131154)

clippy_lints/src/if_let_mutex.rs

@@ -7,6 +7,7 @@ use rustc_errors::Diag;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
+use rustc_span::edition::Edition::Edition2024;
 use rustc_span::sym;
 
 declare_clippy_lint! {
@@ -14,6 +15,12 @@ declare_clippy_lint! {
     /// Checks for `Mutex::lock` calls in `if let` expression
     /// with lock calls in any of the else blocks.
     ///
+    /// ### Disabled starting in Edition 2024
+    /// This lint is effectively disabled starting in
+    /// Edition 2024 as `if let ... else` scoping was reworked
+    /// such that this is no longer an issue. See
+    /// [Proposal: stabilize if_let_rescope for Edition 2024](https://github.com/rust-lang/rust/issues/131154)
+    ///
     /// ### Why is this bad?
     /// The Mutex lock remains held for the whole
     /// `if let ... else` block and deadlocks.
@@ -45,6 +52,10 @@ declare_lint_pass!(IfLetMutex => [IF_LET_MUTEX]);
 
 impl<'tcx> LateLintPass<'tcx> for IfLetMutex {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if cx.tcx.sess.edition() >= Edition2024 {
+            return;
+        }
+
         if let Some(higher::IfLet {
             let_expr,
             if_then,

tests/ui/if_let_mutex.edition2021.stderr

@@ -1,5 +1,5 @@
 error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock
-  --> tests/ui/if_let_mutex.rs:11:5
+  --> tests/ui/if_let_mutex.rs:16:5
    |
 LL |       if let Err(locked) = m.lock() {
    |       ^                    - this Mutex will remain locked for the entire `if let`-block...
@@ -19,7 +19,7 @@ LL | |     };
    = help: to override `-D warnings` add `#[allow(clippy::if_let_mutex)]`
 
 error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock
-  --> tests/ui/if_let_mutex.rs:24:5
+  --> tests/ui/if_let_mutex.rs:29:5
    |
 LL |       if let Some(locked) = m.lock().unwrap().deref() {
    |       ^                     - this Mutex will remain locked for the entire `if let`-block...
@@ -37,7 +37,7 @@ LL | |     };
    = help: move the lock call outside of the `if let ...` expression
 
 error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock
-  --> tests/ui/if_let_mutex.rs:46:5
+  --> tests/ui/if_let_mutex.rs:51:5
    |
 LL |       if let Ok(i) = mutex.lock() {
    |       ^              ----- this Mutex will remain locked for the entire `if let`-block...
@@ -54,7 +54,7 @@ LL | |     };
    = help: move the lock call outside of the `if let ...` expression
 
 error: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock
-  --> tests/ui/if_let_mutex.rs:55:5
+  --> tests/ui/if_let_mutex.rs:60:5
    |
 LL |       if let Ok(_) = m1.lock() {
    |       ^              -- this Mutex will remain locked for the entire `if let`-block...

tests/ui/if_let_mutex.rs

@@ -1,3 +1,8 @@
+//@ compile-flags: -Zunstable-options
+
+//@revisions: edition2021 edition2024
+//@[edition2021] edition:2021
+//@[edition2024] edition:2024
 #![warn(clippy::if_let_mutex)]
 #![allow(clippy::redundant_pattern_matching)]
 
@@ -9,7 +14,7 @@ fn do_stuff<T>(_: T) {}
 fn if_let() {
     let m = Mutex::new(1_u8);
     if let Err(locked) = m.lock() {
-        //~^ ERROR: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a d
+        //~[edition2021]^ if_let_mutex
         do_stuff(locked);
     } else {
         let lock = m.lock().unwrap();
@@ -22,7 +27,7 @@ fn if_let() {
 fn if_let_option() {
     let m = Mutex::new(Some(0_u8));
     if let Some(locked) = m.lock().unwrap().deref() {
-        //~^ ERROR: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a d
+        //~[edition2021]^ if_let_mutex
         do_stuff(locked);
     } else {
         let lock = m.lock().unwrap();
@@ -44,7 +49,7 @@ fn if_let_different_mutex() {
 
 fn mutex_ref(mutex: &Mutex<i32>) {
     if let Ok(i) = mutex.lock() {
-        //~^ ERROR: calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a d
+        //~[edition2021]^ if_let_mutex
         do_stuff(i);
     } else {
         let _x = mutex.lock();