fix missing parenthesis in pretty discriminant

Author: makai410

compiler/rustc_public/src/mir/pretty.rs

@@ -100,7 +100,7 @@ fn pretty_statement<W: Write>(writer: &mut W, statement: &StatementKind) -> io::
             writeln!(writer, "{INDENT}FakeRead({cause:?}, {place:?});")
         }
         StatementKind::SetDiscriminant { place, variant_index } => {
-            writeln!(writer, "{INDENT}discriminant({place:?} = {};", variant_index.to_index())
+            writeln!(writer, "{INDENT}discriminant({place:?}) = {};", variant_index.to_index())
         }
         StatementKind::Deinit(place) => writeln!(writer, "Deinit({place:?};"),
         StatementKind::StorageLive(local) => {

tests/ui/rustc_public-ir-print/async-closure.stdout

@@ -63,7 +63,7 @@ fn foo::{closure#0}::{closure#0}(_1: Pin<&mut {async closure body@$DIR/async-clo
         StorageDead(_3);
         _0 = std::task::Poll::Ready(move _5);
         _10 = CopyForDeref((_1.0: &mut {async closure body@$DIR/async-closure.rs:9:22: 11:6}));
-        discriminant((*_10) = 1;
+        discriminant((*_10)) = 1;
         return;
     }
     bb2: {
@@ -101,7 +101,7 @@ fn foo::{closure#0}::{synthetic#0}(_1: Pin<&mut {async closure body@$DIR/async-c
         StorageDead(_3);
         _0 = std::task::Poll::Ready(move _5);
         _10 = CopyForDeref((_1.0: &mut {async closure body@$DIR/async-closure.rs:9:22: 11:6}));
-        discriminant((*_10) = 1;
+        discriminant((*_10)) = 1;
         return;
     }
     bb2: {