Pretty-print let-else with added parenthesization when needed

Author: dtolnay

Diff for: compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1238,7 +1238,11 @@ impl<'a> State<'a> {
                 if let Some((init, els)) = loc.kind.init_else_opt() {
                     self.nbsp();
                     self.word_space("=");
-                    self.print_expr(init, FixupContext::default());
+                    self.print_expr_cond_paren(
+                        init,
+                        els.is_some() && classify::expr_trailing_brace(init).is_some(),
+                        FixupContext::default(),
+                    );
                     if let Some(els) = els {
                         self.cbox(INDENT_UNIT);
                         self.ibox(INDENT_UNIT);

Diff for: tests/ui/unpretty/let-else.stdout

@@ -11,5 +11,5 @@ macro_rules! expr { ($e:expr) => { $e }; }
 
 fn main() {
     let _ = 1 + 1 else { return; };
-    let _ = loop {} else { return; };
+    let _ = (loop {}) else { return; };
 }