Incorporated comments from @felixmulder

Author: Enno Runne

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -404,13 +404,13 @@ object Parsers {
 
     var opStack: List[OpInfo] = Nil
 
-    def checkAssoc(offset: Int, op: Name, leftAssoc: Boolean, op2: Name) =
-      if (isLeftAssoc(op) != leftAssoc)
-        syntaxError(MixedLeftAndRightAssociativeOps(op, op2, leftAssoc), offset)
+    def checkAssoc(offset: Token, op1: Name, op2: Name, op2LeftAssoc: Boolean): Unit =
+      if (isLeftAssoc(op1) != op2LeftAssoc)
+        syntaxError(MixedLeftAndRightAssociativeOps(op1, op2, op2LeftAssoc), offset)
 
     def reduceStack(base: List[OpInfo], top: Tree, prec: Int, leftAssoc: Boolean, op2: Name): Tree = {
       if (opStack != base && precedence(opStack.head.operator.name) == prec)
-        checkAssoc(opStack.head.offset, opStack.head.operator.name, leftAssoc, op2)
+        checkAssoc(opStack.head.offset, opStack.head.operator.name, op2, leftAssoc)
       def recur(top: Tree): Tree = {
         if (opStack == base) top
         else {

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1098,20 +1098,21 @@ object messages {
     val kind = "Syntax"
     val op1Asso = if (op2LeftAssoc) "which is right-associative" else "which is left-associative"
     val op2Asso = if (op2LeftAssoc) "which is left-associative" else "which is right-associative"
-    val msg = s"${hl"`${op1}`"} (${op1Asso}) and ${hl"`${op2}`"} ($op2Asso) have same precedence and may not be mixed"
+    val msg = s"`${op1}` (${op1Asso}) and `${op2}` ($op2Asso) have same precedence and may not be mixed"
     val explanation =
-      s"""|The operators ${hl"${op1}"} and ${hl"${op2}"} are used as infix operators in the same expression,
+      s"""|The operators ${op1} and ${op2} are used as infix operators in the same expression,
           |but they bind to different sides:
-          |${hl"${op1}"} is applied to the operand to its ${if (op2LeftAssoc) "right" else "left"}
-          |${hl"${op2}"} is applied to the operand to its ${if (op2LeftAssoc) "left" else "right"}
+          |${op1} is applied to the operand to its ${if (op2LeftAssoc) "right" else "left"}
+          |${op2} is applied to the operand to its ${if (op2LeftAssoc) "left" else "right"}
           |As both have the same precedence the compiler can't decide which to apply first.
           |
           |You may use parenthesis to make the application order explicit,
-          |or use method application syntax ${hl"`operand1.${op1}(operand2)`"}.
+          |or use method application syntax `operand1.${op1}(operand2)`.
           |
           |Operators ending in a colon `:` are right-associative. All other operators are left-associative.
           |
-          |Infix operator precedence is determined by the operator's first character:
+          |Infix operator precedence is determined by the operator's first character. Characters are listed
+          |below in increasing order of precedence, with characters on the same line having the same precedence.
           |  (all letters)
           |  |
           |  ^
@@ -1122,7 +1123,7 @@ object messages {
           |  + -
           |  * / %
           |  (all other special characters)
-          |Operators starting with a letter have lowest precedence, followed by operators starting with `|', etc.
+          |Operators starting with a letter have lowest precedence, followed by operators starting with `|`, etc.
           |""".stripMargin
   }