Pretty-print parenthesis around binary in postfix match

Signed-off-by: Sasha Pourcelot <sasha.pourcelot@protonmail.com>

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -488,7 +488,7 @@ impl<'a> State<'a> {
                         self.space();
                     }
                     MatchKind::Postfix => {
-                        self.print_expr_as_cond(expr);
+                        self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX, fixup);
                         self.word_nbsp(".match");
                     }
                 }

tests/pretty/postfix-match/precedence.pp

@@ -0,0 +1,34 @@
+#![feature(prelude_import)]
+#![no_std]
+#![feature(postfix_match)]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+
+use std::ops::Add;
+
+//@ pretty-mode:expanded
+//@ pp-exact:precedence.pp
+
+macro_rules! repro { ($e:expr) => { $e.match { _ => {} } }; }
+
+struct Struct {}
+
+impl Add<Struct> for usize {
+    type Output = ();
+    fn add(self, _: Struct) -> () { () }
+}
+pub fn main() {
+    let a;
+    (
+        { 1 } + 1).match {
+        _ => {}
+    };
+    (4 as usize).match { _ => {} };
+    (return).match { _ => {} };
+    (a = 42).match { _ => {} };
+    (|| {}).match { _ => {} };
+    (42..101).match { _ => {} };
+    (1 + Struct {}).match { _ => {} };
+}

tests/pretty/postfix-match/precedence.rs

@@ -0,0 +1,34 @@
+#![feature(postfix_match)]
+
+use std::ops::Add;
+
+//@ pretty-mode:expanded
+//@ pp-exact:precedence.pp
+
+macro_rules! repro {
+    ($e:expr) => {
+        $e.match {
+            _ => {}
+        }
+    };
+}
+
+struct Struct {}
+
+impl Add<Struct> for usize {
+    type Output = ();
+    fn add(self, _: Struct) -> () {
+        ()
+    }
+}
+pub fn main() {
+    let a;
+
+    repro!({ 1 } + 1);
+    repro!(4 as usize);
+    repro!(return);
+    repro!(a = 42);
+    repro!(|| {});
+    repro!(42..101);
+    repro!(1 + Struct {});
+}