From c67a34b9e509b76ff145526f28a20f9495c2ab61 Mon Sep 17 00:00:00 2001
From: Garming Sam <garming_sam@outlook.com>
Date: Thu, 6 Aug 2015 18:43:02 +1200
Subject: [PATCH 1/4] Binary ops should add parenthesis to each side

Otherwise, we get (1 + 2) * 3 looking like 1 + 2 * 3
---
 src/libsyntax/print/pprust.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 3b8ee91374c..147314739f8 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1670,10 +1670,10 @@ impl<'a> State<'a> {
                          op: ast::BinOp,
                          lhs: &ast::Expr,
                          rhs: &ast::Expr) -> io::Result<()> {
-        try!(self.print_expr(lhs));
+        try!(self.print_expr_maybe_paren(lhs));
         try!(space(&mut self.s));
         try!(self.word_space(ast_util::binop_to_string(op.node)));
-        self.print_expr(rhs)
+        self.print_expr_maybe_paren(rhs)
     }
 
     fn print_expr_unary(&mut self,

From c0c6af7f073620aacfb103c070e997a8d50b7201 Mon Sep 17 00:00:00 2001
From: Garming Sam <garming_sam@outlook.com>
Date: Thu, 6 Aug 2015 19:55:27 +1200
Subject: [PATCH 2/4] Add operator precedence for pretty printer

Previously it just added parentheses in excess.
e.g. ((1 + 2) + 3) + 4
---
 src/libsyntax/print/pprust.rs | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 147314739f8..b3fd05325b1 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1555,6 +1555,21 @@ impl<'a> State<'a> {
         self.pclose()
     }
 
+    pub fn check_expr_bin_needs_paren(&mut self, sub_expr: &ast::Expr,
+                                      binop: ast::BinOp) -> bool {
+        match sub_expr.node {
+            ast::ExprBinary(ref sub_op, _, _) => {
+                if ast_util::operator_prec(sub_op.node) <
+                    ast_util::operator_prec(binop.node) {
+                    true
+                } else {
+                    false
+                }
+            }
+            _ => true
+        }
+    }
+
     pub fn print_expr_maybe_paren(&mut self, expr: &ast::Expr) -> io::Result<()> {
         let needs_par = needs_parentheses(expr);
         if needs_par {
@@ -1670,10 +1685,18 @@ impl<'a> State<'a> {
                          op: ast::BinOp,
                          lhs: &ast::Expr,
                          rhs: &ast::Expr) -> io::Result<()> {
-        try!(self.print_expr_maybe_paren(lhs));
+        if self.check_expr_bin_needs_paren(lhs, op) {
+            try!(self.print_expr_maybe_paren(lhs));
+        } else {
+            try!(self.print_expr(lhs));
+        }
         try!(space(&mut self.s));
         try!(self.word_space(ast_util::binop_to_string(op.node)));
-        self.print_expr_maybe_paren(rhs)
+        if self.check_expr_bin_needs_paren(rhs, op) {
+            self.print_expr_maybe_paren(rhs)
+        } else {
+            self.print_expr(rhs)
+        }
     }
 
     fn print_expr_unary(&mut self,

From 6a51de0a0a846524dc76b027f52f0afec1597383 Mon Sep 17 00:00:00 2001
From: Garming Sam <garming_sam@outlook.com>
Date: Thu, 6 Aug 2015 19:57:41 +1200
Subject: [PATCH 3/4] Casts are a type of binop

This just adds paren following the same cases as before
---
 src/libsyntax/print/pprust.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index b3fd05325b1..d59ab2ba565 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1753,7 +1753,7 @@ impl<'a> State<'a> {
                 try!(self.print_literal(&**lit));
             }
             ast::ExprCast(ref expr, ref ty) => {
-                try!(self.print_expr(&**expr));
+                try!(self.print_expr_maybe_paren(&**expr));
                 try!(space(&mut self.s));
                 try!(self.word_space("as"));
                 try!(self.print_type(&**ty));

From 22baa46f784856b6d6bb4374bcc3fb4b66bb8097 Mon Sep 17 00:00:00 2001
From: Garming Sam <garming_sam@outlook.com>
Date: Mon, 10 Aug 2015 04:45:57 +1200
Subject: [PATCH 4/4] Avoid adding extra paren with two casts

---
 src/libsyntax/print/pprust.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index d59ab2ba565..7919bd45ced 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1753,7 +1753,11 @@ impl<'a> State<'a> {
                 try!(self.print_literal(&**lit));
             }
             ast::ExprCast(ref expr, ref ty) => {
-                try!(self.print_expr_maybe_paren(&**expr));
+                if let ast::ExprCast(..) = expr.node {
+                    try!(self.print_expr(&**expr));
+                } else {
+                    try!(self.print_expr_maybe_paren(&**expr));
+                }
                 try!(space(&mut self.s));
                 try!(self.word_space("as"));
                 try!(self.print_type(&**ty));