Use single source of truth for expr precedence

Introduce a new unified type that holds the expression precedence for
both AST and HIR nodes.

src/libsyntax/util/parser.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 use parse::token::{Token, BinOpToken};
 use symbol::keywords;
-use ast::{self, BinOpKind, ExprKind};
+use ast::{self, BinOpKind};
 
 /// Associative operator with precedence.
 ///
@@ -228,66 +228,6 @@ pub const PREC_POSTFIX: i8 = 60;
 pub const PREC_PAREN: i8 = 99;
 pub const PREC_FORCE_PAREN: i8 = 100;
 
-pub fn expr_precedence(expr: &ast::Expr) -> i8 {
-    match expr.node {
-        ExprKind::Closure(..) => PREC_CLOSURE,
-
-        ExprKind::Break(..) |
-        ExprKind::Continue(..) |
-        ExprKind::Ret(..) |
-        ExprKind::Yield(..) => PREC_JUMP,
-
-        // `Range` claims to have higher precedence than `Assign`, but `x .. x = x` fails to parse,
-        // instead of parsing as `(x .. x) = x`.  Giving `Range` a lower precedence ensures that
-        // `pprust` will add parentheses in the right places to get the desired parse.
-        ExprKind::Range(..) => PREC_RANGE,
-
-        // Binop-like expr kinds, handled by `AssocOp`.
-        ExprKind::Binary(op, _, _) =>
-            AssocOp::from_ast_binop(op.node).precedence() as i8,
-
-        ExprKind::InPlace(..) => AssocOp::Inplace.precedence() as i8,
-        ExprKind::Cast(..) => AssocOp::As.precedence() as i8,
-        ExprKind::Type(..) => AssocOp::Colon.precedence() as i8,
-
-        ExprKind::Assign(..) |
-        ExprKind::AssignOp(..) => AssocOp::Assign.precedence() as i8,
-
-        // Unary, prefix
-        ExprKind::Box(..) |
-        ExprKind::AddrOf(..) |
-        ExprKind::Unary(..) => PREC_PREFIX,
-
-        // Unary, postfix
-        ExprKind::Call(..) |
-        ExprKind::MethodCall(..) |
-        ExprKind::Field(..) |
-        ExprKind::TupField(..) |
-        ExprKind::Index(..) |
-        ExprKind::Try(..) |
-        ExprKind::InlineAsm(..) |
-        ExprKind::Mac(..) => PREC_POSTFIX,
-
-        // Never need parens
-        ExprKind::Array(..) |
-        ExprKind::Repeat(..) |
-        ExprKind::Tup(..) |
-        ExprKind::Lit(..) |
-        ExprKind::Path(..) |
-        ExprKind::Paren(..) |
-        ExprKind::If(..) |
-        ExprKind::IfLet(..) |
-        ExprKind::While(..) |
-        ExprKind::WhileLet(..) |
-        ExprKind::ForLoop(..) |
-        ExprKind::Loop(..) |
-        ExprKind::Match(..) |
-        ExprKind::Block(..) |
-        ExprKind::Catch(..) |
-        ExprKind::Struct(..) => PREC_PAREN,
-    }
-}
-
 /// Expressions that syntactically contain an "exterior" struct literal i.e. not surrounded by any
 /// parens or other delimiters, e.g. `X { y: 1 }`, `X { y: 1 }.method()`, `foo == X { y: 1 }` and
 /// `X { y: 1 } == foo` all do, but `(X { y: 1 }) == foo` does not.