Fix missing terminator for slice pattern

crates/hir-ty/src/mir/lower/pattern_matching.rs

@@ -206,6 +206,8 @@ impl MirLowerCtx<'_> {
                 (current, current_else)
             }
             Pat::Slice { prefix, slice, suffix } => {
+                if mode == MatchingMode::Check {
+                    // emit runtime length check for slice
                     if let TyKind::Slice(_) = self.infer[pattern].kind(Interner) {
                         let pattern_len = prefix.len() + suffix.len();
                         let place_len: Place =
@@ -216,7 +218,8 @@ impl MirLowerCtx<'_> {
                             Rvalue::Len((&mut cond_place).clone()),
                             pattern.into(),
                         );
-                    let else_target = *current_else.get_or_insert_with(|| self.new_basic_block());
+                        let else_target =
+                            *current_else.get_or_insert_with(|| self.new_basic_block());
                         let next = self.new_basic_block();
                         if slice.is_none() {
                             self.set_terminator(
@@ -257,6 +260,7 @@ impl MirLowerCtx<'_> {
                         }
                         current = next;
                     }
+                }
                 for (i, &pat) in prefix.iter().enumerate() {
                     let next_place = (&mut cond_place).project(ProjectionElem::ConstantIndex {
                         offset: i as u64,

crates/ide-diagnostics/src/handlers/mutability_errors.rs

@@ -993,6 +993,27 @@ fn f() {
         );
     }
 
+    #[test]
+    fn slice_pattern() {
+        check_diagnostics(
+            r#"
+//- minicore: coerce_unsized, deref_mut, slice, copy
+fn x(t: &[u8]) {
+    match t {
+        &[a, mut b] | &[a, _, mut b] => {
+           //^^^^^ 💡 weak: variable does not need to be mutable
+
+            a = 2;
+          //^^^^^ 💡 error: cannot mutate immutable variable `a`
+
+        }
+        _ => {}
+    }
+}
+            "#,
+        );
+    }
+
     #[test]
     fn boxes() {
         check_diagnostics(