Use same priority for type operators, as mandated by the spec

Author: Blaisorblade

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

@@ -9,6 +9,9 @@ package object parsing {
 
   def precedence(operator: Name, isType: Boolean = false): Int =
     if (operator eq nme.ERROR) -1
+    /* SLS 3.2.10 (https://www.scala-lang.org/files/archive/spec/2.13/03-types.html#infix-types):
+     * all infix types have the same precedence */
+    else if (isType) minInfixPrec
     else {
       val firstCh = operator.firstPart.head
       if (isScalaLetter(firstCh)) 1

compiler/test-resources/type-printer/infix

@@ -32,11 +32,11 @@ scala> import scala.annotation.showAsInfix
 scala> @scala.annotation.showAsInfix class Mappy[T,U]
 // defined class Mappy
 scala> def foo: (Int Mappy Boolean) && String = ???
-def foo: (Int Mappy Boolean) && String
+def foo: Int Mappy Boolean && String
 scala> def foo: Int Mappy Boolean && String = ???
 def foo: Int Mappy Boolean && String
 scala> def foo: Int Mappy (Boolean && String) = ???
-def foo: Int Mappy Boolean && String
+def foo: Int Mappy (Boolean && String)
 scala> @scala.annotation.showAsInfix(false) class ||[T,U]
 // defined class ||
 scala> def foo: Int || Boolean = ???