Parse unary operators as regular identifiers when followed by square brackets

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

@@ -2217,6 +2217,7 @@ object Parsers {
     val prefixExpr: Location => Tree = location =>
       if isIdent && nme.raw.isUnary(in.name)
          && in.canStartExprTokens.contains(in.lookahead.token)
+          && in.lookahead.token != LBRACKET
       then
         val start = in.offset
         val op = termIdent()

tests/pos/unary-with-type-params.scala

@@ -0,0 +1,5 @@
+object Test {
+  def +[T](x: T): String = "x"
+  +[Int](6): String // Parser can treat + as identifier in non-unary context
+  +(6): Int // Parser prioritizes + as unary when possible
+}