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/ast.rs

@@ -15,6 +15,17 @@ pub use self::UnsafeSource::*;
 pub use self::PathParameters::*;
 pub use symbol::{Ident, Symbol as Name};
 pub use util::ThinVec;
+pub use util::parser::{
+    AssocOp,
+    PREC_RESET,
+    PREC_CLOSURE,
+    PREC_JUMP,
+    PREC_RANGE,
+    PREC_PREFIX,
+    PREC_POSTFIX,
+    PREC_PAREN,
+    PREC_FORCE_PAREN,
+};
 
 use syntax_pos::{Span, DUMMY_SP};
 use codemap::{respan, Spanned};
@@ -28,6 +39,7 @@ use tokenstream::{ThinTokenStream, TokenStream};
 
 use serialize::{self, Encoder, Decoder};
 use std::collections::HashSet;
+use std::cmp::Ordering;
 use std::fmt;
 use std::rc::Rc;
 use std::u32;
@@ -730,6 +742,7 @@ impl BinOpKind {
             _ => false
         }
     }
+
     pub fn is_comparison(&self) -> bool {
         use self::BinOpKind::*;
         match *self {
@@ -740,6 +753,7 @@ impl BinOpKind {
             false,
         }
     }
+
     /// Returns `true` if the binary operator takes its arguments by value
     pub fn is_by_value(&self) -> bool {
         !self.is_comparison()
@@ -903,6 +917,129 @@ pub struct Expr {
     pub attrs: ThinVec<Attribute>
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ExprPrecedence {
+    Closure,
+    Break,
+    Continue,
+    Ret,
+    Yield,
+
+    Range,
+
+    Binary(BinOpKind),
+
+    InPlace,
+    Cast,
+    Type,
+
+    Assign,
+    AssignOp,
+
+    Box,
+    AddrOf,
+    Unary,
+
+    Call,
+    MethodCall,
+    Field,
+    TupField,
+    Index,
+    Try,
+    InlineAsm,
+    Mac,
+
+    Array,
+    Repeat,
+    Tup,
+    Lit,
+    Path,
+    Paren,
+    If,
+    IfLet,
+    While,
+    WhileLet,
+    ForLoop,
+    Loop,
+    Match,
+    Block,
+    Catch,
+    Struct,
+}
+
+impl PartialOrd for ExprPrecedence {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.order().cmp(&other.order()))
+    }
+}
+
+impl Ord for ExprPrecedence {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.order().cmp(&other.order())
+    }
+}
+
+impl ExprPrecedence {
+    pub fn order(self) -> i8 {
+        match self {
+            ExprPrecedence::Closure => PREC_CLOSURE,
+
+            ExprPrecedence::Break |
+            ExprPrecedence::Continue |
+            ExprPrecedence::Ret |
+            ExprPrecedence::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.
+            ExprPrecedence::Range => PREC_RANGE,
+
+            // Binop-like expr kinds, handled by `AssocOp`.
+            ExprPrecedence::Binary(op) => AssocOp::from_ast_binop(op).precedence() as i8,
+            ExprPrecedence::InPlace => AssocOp::Inplace.precedence() as i8,
+            ExprPrecedence::Cast => AssocOp::As.precedence() as i8,
+            ExprPrecedence::Type => AssocOp::Colon.precedence() as i8,
+
+            ExprPrecedence::Assign |
+            ExprPrecedence::AssignOp => AssocOp::Assign.precedence() as i8,
+
+            // Unary, prefix
+            ExprPrecedence::Box |
+            ExprPrecedence::AddrOf |
+            ExprPrecedence::Unary => PREC_PREFIX,
+
+            // Unary, postfix
+            ExprPrecedence::Call |
+            ExprPrecedence::MethodCall |
+            ExprPrecedence::Field |
+            ExprPrecedence::TupField |
+            ExprPrecedence::Index |
+            ExprPrecedence::Try |
+            ExprPrecedence::InlineAsm |
+            ExprPrecedence::Mac => PREC_POSTFIX,
+
+            // Never need parens
+            ExprPrecedence::Array |
+            ExprPrecedence::Repeat |
+            ExprPrecedence::Tup |
+            ExprPrecedence::Lit |
+            ExprPrecedence::Path |
+            ExprPrecedence::Paren |
+            ExprPrecedence::If |
+            ExprPrecedence::IfLet |
+            ExprPrecedence::While |
+            ExprPrecedence::WhileLet |
+            ExprPrecedence::ForLoop |
+            ExprPrecedence::Loop |
+            ExprPrecedence::Match |
+            ExprPrecedence::Block |
+            ExprPrecedence::Catch |
+            ExprPrecedence::Struct => PREC_PAREN,
+        }
+    }
+}
+
 impl Expr {
     /// Wether this expression would be valid somewhere that expects a value, for example, an `if`
     /// condition.
@@ -966,6 +1103,49 @@ impl Expr {
 
         Some(P(Ty { node, id: self.id, span: self.span }))
     }
+
+    pub fn precedence(&self) -> ExprPrecedence {
+        match self.node {
+            ExprKind::Box(_) => ExprPrecedence::Box,
+            ExprKind::InPlace(..) => ExprPrecedence::InPlace,
+            ExprKind::Array(_) => ExprPrecedence::Array,
+            ExprKind::Call(..) => ExprPrecedence::Call,
+            ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
+            ExprKind::Tup(_) => ExprPrecedence::Tup,
+            ExprKind::Binary(op, ..) => ExprPrecedence::Binary(op.node),
+            ExprKind::Unary(..) => ExprPrecedence::Unary,
+            ExprKind::Lit(_) => ExprPrecedence::Lit,
+            ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
+            ExprKind::If(..) => ExprPrecedence::If,
+            ExprKind::IfLet(..) => ExprPrecedence::IfLet,
+            ExprKind::While(..) => ExprPrecedence::While,
+            ExprKind::WhileLet(..) => ExprPrecedence::WhileLet,
+            ExprKind::ForLoop(..) => ExprPrecedence::ForLoop,
+            ExprKind::Loop(..) => ExprPrecedence::Loop,
+            ExprKind::Match(..) => ExprPrecedence::Match,
+            ExprKind::Closure(..) => ExprPrecedence::Closure,
+            ExprKind::Block(..) => ExprPrecedence::Block,
+            ExprKind::Catch(..) => ExprPrecedence::Catch,
+            ExprKind::Assign(..) => ExprPrecedence::Assign,
+            ExprKind::AssignOp(..) => ExprPrecedence::AssignOp,
+            ExprKind::Field(..) => ExprPrecedence::Field,
+            ExprKind::TupField(..) => ExprPrecedence::TupField,
+            ExprKind::Index(..) => ExprPrecedence::Index,
+            ExprKind::Range(..) => ExprPrecedence::Range,
+            ExprKind::Path(..) => ExprPrecedence::Path,
+            ExprKind::AddrOf(..) => ExprPrecedence::AddrOf,
+            ExprKind::Break(..) => ExprPrecedence::Break,
+            ExprKind::Continue(..) => ExprPrecedence::Continue,
+            ExprKind::Ret(..) => ExprPrecedence::Ret,
+            ExprKind::InlineAsm(..) => ExprPrecedence::InlineAsm,
+            ExprKind::Mac(..) => ExprPrecedence::Mac,
+            ExprKind::Struct(..) => ExprPrecedence::Struct,
+            ExprKind::Repeat(..) => ExprPrecedence::Repeat,
+            ExprKind::Paren(..) => ExprPrecedence::Paren,
+            ExprKind::Try(..) => ExprPrecedence::Try,
+            ExprKind::Yield(..) => ExprPrecedence::Yield,
+        }
+    }
 }
 
 impl fmt::Debug for Expr {