Inline ExprPrecedence::order into Expr::precedence

compiler/rustc_hir/src/hir.rs

@@ -1,7 +1,7 @@
 use std::fmt;
 
 use rustc_abi::ExternAbi;
-use rustc_ast::util::parser::ExprPrecedence;
+use rustc_ast::util::parser::{AssocOp, PREC_CLOSURE, PREC_JUMP, PREC_PREFIX, PREC_UNAMBIGUOUS};
 use rustc_ast::{
     self as ast, Attribute, FloatTy, InlineAsmOptions, InlineAsmTemplatePiece, IntTy, Label,
     LitKind, TraitObjectSyntax, UintTy,
@@ -1719,41 +1719,54 @@ pub struct Expr<'hir> {
 }
 
 impl Expr<'_> {
-    pub fn precedence(&self) -> ExprPrecedence {
+    pub fn precedence(&self) -> i8 {
         match self.kind {
-            ExprKind::ConstBlock(_) => ExprPrecedence::ConstBlock,
-            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::Cast(..) => ExprPrecedence::Cast,
+            ExprKind::Closure { .. } => PREC_CLOSURE,
+
+            ExprKind::Break(..)
+            | ExprKind::Continue(..)
+            | ExprKind::Ret(..)
+            | ExprKind::Yield(..)
+            | ExprKind::Become(..) => PREC_JUMP,
+
+            // Binop-like expr kinds, handled by `AssocOp`.
+            ExprKind::Binary(op, ..) => AssocOp::from_ast_binop(op.node).precedence() as i8,
+            ExprKind::Cast(..) => AssocOp::As.precedence() as i8,
+
+            ExprKind::Assign(..) |
+            ExprKind::AssignOp(..) => AssocOp::Assign.precedence() as i8,
+
+            // Unary, prefix
+            ExprKind::AddrOf(..)
+            // Here `let pats = expr` has `let pats =` as a "unary" prefix of `expr`.
+            // However, this is not exactly right. When `let _ = a` is the LHS of a binop we
+            // need parens sometimes. E.g. we can print `(let _ = a) && b` as `let _ = a && b`
+            // but we need to print `(let _ = a) < b` as-is with parens.
+            | ExprKind::Let(..)
+            | ExprKind::Unary(..) => PREC_PREFIX,
+
+            // Never need parens
+            ExprKind::Array(_)
+            | ExprKind::Block(..)
+            | ExprKind::Call(..)
+            | ExprKind::ConstBlock(_)
+            | ExprKind::Field(..)
+            | ExprKind::If(..)
+            | ExprKind::Index(..)
+            | ExprKind::InlineAsm(..)
+            | ExprKind::Lit(_)
+            | ExprKind::Loop(..)
+            | ExprKind::Match(..)
+            | ExprKind::MethodCall(..)
+            | ExprKind::OffsetOf(..)
+            | ExprKind::Path(..)
+            | ExprKind::Repeat(..)
+            | ExprKind::Struct(..)
+            | ExprKind::Tup(_)
+            | ExprKind::Type(..)
+            | ExprKind::Err(_) => PREC_UNAMBIGUOUS,
+
             ExprKind::DropTemps(ref expr, ..) => expr.precedence(),
-            ExprKind::If(..) => ExprPrecedence::If,
-            ExprKind::Let(..) => ExprPrecedence::Let,
-            ExprKind::Loop(..) => ExprPrecedence::Loop,
-            ExprKind::Match(..) => ExprPrecedence::Match,
-            ExprKind::Closure { .. } => ExprPrecedence::Closure,
-            ExprKind::Block(..) => ExprPrecedence::Block,
-            ExprKind::Assign(..) => ExprPrecedence::Assign,
-            ExprKind::AssignOp(..) => ExprPrecedence::AssignOp,
-            ExprKind::Field(..) => ExprPrecedence::Field,
-            ExprKind::Index(..) => ExprPrecedence::Index,
-            ExprKind::Path(..) => ExprPrecedence::Path,
-            ExprKind::AddrOf(..) => ExprPrecedence::AddrOf,
-            ExprKind::Break(..) => ExprPrecedence::Break,
-            ExprKind::Continue(..) => ExprPrecedence::Continue,
-            ExprKind::Ret(..) => ExprPrecedence::Ret,
-            ExprKind::Become(..) => ExprPrecedence::Become,
-            ExprKind::Struct(..) => ExprPrecedence::Struct,
-            ExprKind::Repeat(..) => ExprPrecedence::Repeat,
-            ExprKind::Yield(..) => ExprPrecedence::Yield,
-            ExprKind::Type(..) | ExprKind::InlineAsm(..) | ExprKind::OffsetOf(..) => {
-                ExprPrecedence::Mac
-            }
-            ExprKind::Err(_) => ExprPrecedence::Err,
         }
     }