Change comparison operators to have Fixity::None

Author: dtolnay

compiler/rustc_ast/src/util/parser.rs

@@ -153,9 +153,10 @@ impl AssocOp {
         match *self {
             Assign | AssignOp(_) => Fixity::Right,
             As | Multiply | Divide | Modulus | Add | Subtract | ShiftLeft | ShiftRight | BitAnd
-            | BitXor | BitOr | Less | Greater | LessEqual | GreaterEqual | Equal | NotEqual
-            | LAnd | LOr => Fixity::Left,
-            DotDot | DotDotEq => Fixity::None,
+            | BitXor | BitOr | LAnd | LOr => Fixity::Left,
+            Less | Greater | LessEqual | GreaterEqual | Equal | NotEqual | DotDot | DotDotEq => {
+                Fixity::None
+            }
         }
     }
 

compiler/rustc_parse/src/parser/expr.rs

@@ -279,13 +279,9 @@ impl<'a> Parser<'a> {
                 break;
             }
 
-            let fixity = op.fixity();
-            let min_prec = match fixity {
+            let min_prec = match op.fixity() {
                 Fixity::Right => Bound::Included(prec),
-                Fixity::Left => Bound::Excluded(prec),
-                // We currently have no non-associative operators that are not handled above by
-                // the special cases. The code is here only for future convenience.
-                Fixity::None => Bound::Excluded(prec),
+                Fixity::Left | Fixity::None => Bound::Excluded(prec),
             };
             let (rhs, _) = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
                 let attrs = this.parse_outer_attributes()?;
@@ -337,10 +333,6 @@ impl<'a> Parser<'a> {
                     self.dcx().span_bug(span, "AssocOp should have been handled by special case")
                 }
             };
-
-            if let Fixity::None = fixity {
-                break;
-            }
         }
 
         Ok((lhs, parsed_something))

tests/ui-fulldeps/pprust-parenthesis-insertion.rs

@@ -97,6 +97,8 @@ static EXPRS: &[&str] = &[
     "2..(2..2)",
     "(2..2)..",
     "..(2..2)",
+    // Grammar restriction: comparison operators cannot be chained (1 < 2 == false).
+    "((1 < 2) == false) as usize",
     // Grammar restriction: the value in let-else is not allowed to end in a
     // curly brace.
     "{ let _ = 1 + 1 else {}; }",
@@ -121,10 +123,6 @@ static EXPRS: &[&str] = &[
     "if let _ = () && (Struct {}).x {}",
     */
     /*
-    // FIXME: pretty-printer produces invalid syntax. `(1 < 2 == false) as usize`
-    "((1 < 2) == false) as usize",
-    */
-    /*
     // FIXME: pretty-printer produces invalid syntax. `for _ in 1..{ 2 } {}`
     "for _ in (1..{ 2 }) {}",
     */