fix unnecessary_semicolon: don't lint on stmts with attrs (rust-lang#15466)

fixes rust-lang#15426

changelog: [`unnecessary_semicolon`]: don't lint on statements with
attributes

Author: dswij

clippy_lints/src/unnecessary_semicolon.rs

@@ -86,7 +86,9 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessarySemicolon {
                 expr.kind,
                 ExprKind::If(..) | ExprKind::Match(_, _, MatchSource::Normal | MatchSource::Postfix)
             )
-            && cx.typeck_results().expr_ty(expr) == cx.tcx.types.unit
+            && cx.typeck_results().expr_ty(expr).is_unit()
+            // if a stmt has attrs, then turning it into an expr will break the code, since attrs aren't allowed on exprs
+            && cx.tcx.hir_attrs(stmt.hir_id).is_empty()
         {
             if let Some(block_is_unit) = self.is_last_in_block(stmt) {
                 if cx.tcx.sess.edition() <= Edition2021 && leaks_droppable_temporary_with_limited_lifetime(cx, expr) {

tests/ui/unnecessary_semicolon.edition2021.fixed

@@ -63,3 +63,12 @@ fn issue14100() -> bool {
     // cast into the `bool` function return type.
     if return true {};
 }
+
+fn issue15426(x: u32) {
+    // removing the `;` would turn the stmt into an expr, but attrs aren't allowed on exprs
+    #[rustfmt::skip]
+    match x {
+        0b00 => {}  0b01 => {}
+        0b11 => {}  _    => {}
+    };
+}

tests/ui/unnecessary_semicolon.edition2024.fixed

@@ -63,3 +63,12 @@ fn issue14100() -> bool {
     // cast into the `bool` function return type.
     if return true {};
 }
+
+fn issue15426(x: u32) {
+    // removing the `;` would turn the stmt into an expr, but attrs aren't allowed on exprs
+    #[rustfmt::skip]
+    match x {
+        0b00 => {}  0b01 => {}
+        0b11 => {}  _    => {}
+    };
+}

tests/ui/unnecessary_semicolon.rs

@@ -63,3 +63,12 @@ fn issue14100() -> bool {
     // cast into the `bool` function return type.
     if return true {};
 }
+
+fn issue15426(x: u32) {
+    // removing the `;` would turn the stmt into an expr, but attrs aren't allowed on exprs
+    #[rustfmt::skip]
+    match x {
+        0b00 => {}  0b01 => {}
+        0b11 => {}  _    => {}
+    };
+}