Address review comments

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1710,10 +1710,12 @@ impl<'a> State<'a> {
                 }
             }
             PatKind::Guard(subpat, condition) => {
+                self.popen();
                 self.print_pat(subpat);
                 self.space();
                 self.word_space("if");
                 self.print_expr(condition, FixupContext::default());
+                self.pclose();
             }
             PatKind::Slice(elts) => {
                 self.word("[");

tests/ui/pattern/rfc-3637-guard-patterns/macro-rules.rs

@@ -0,0 +1,20 @@
+//@ run-pass
+//! Tests that the addition of guard patterns does not change the behavior of the `pat` macro
+//! fragment.
+#![feature(guard_patterns)]
+#![allow(incomplete_features)]
+
+macro_rules! has_guard {
+    ($p:pat) => {
+        false
+    };
+    ($p:pat if $e:expr) => {
+        true
+    };
+}
+
+fn main() {
+    assert_eq!(has_guard!(Some(_)), false);
+    assert_eq!(has_guard!(Some(_) if true), true);
+    assert_eq!(has_guard!((Some(_) if true)), false);
+}