Don't escape format anchors with no interpolations

Author: jcracknell

src/main/scala/com/typesafe/scalalogging/LoggerMacro.scala

@@ -239,8 +239,13 @@ private object LoggerMacro {
 
     message.tree match {
       case q"scala.StringContext.apply(..$parts).s(..$args)" =>
-        // Emulate standard interpolator escaping and escape literal slf4j format anchors
-        val messageFormat = parts.map({ case Literal(Constant(s: String)) => StringContext.treatEscapes(s).replace("{}", "\\{}") }).mkString("{}")
+        val messageFormat = parts.iterator.map({ case Literal(Constant(str: String)) => str })
+          // Emulate standard interpolator escaping
+          .map(StringContext.treatEscapes)
+          // Escape literal slf4j format anchors if the resulting call will require a format string
+          .map(str => if (args.nonEmpty) str.replace("{}", "\\{}") else str)
+          .mkString("{}")
+
         (c.Expr(q"$messageFormat"), args map { arg =>
           // Box interpolated AnyVals by explicitly getting the string representation
           c.Expr[Any](if (arg.tpe <:< weakTypeOf[AnyVal]) q"$arg.toString" else arg)

src/test/scala/com/typesafe/scalalogging/LoggerSpec.scala

@@ -68,13 +68,18 @@ class LoggerSpec extends WordSpec with Matchers with MockitoSugar {
       verify(underlying).error("msg {}", 1.toString)
     }
 
-    "call the underlying logger's error method preserving literal format anchors when the message is interpolated" in {
+    "call the underlying logger's error method escaping literal format anchors" in {
       val f = fixture(_.isErrorEnabled, true)
       import f._
       logger.error(s"foo {} bar $arg1")
       verify(underlying).error("foo \\{} bar {}", arg1)
     }
-
+    "call the underlying logger's error method without escaping format anchors when the message has no interpolations" in {
+      val f = fixture(_.isErrorEnabled, true)
+      import f._
+      logger.error(s"foo {} bar")
+      verify(underlying).error("foo {} bar")
+    }
     "call the underlying logger's error method when the interpolated string contains escape sequences" in {
       val f = fixture(_.isErrorEnabled, true)
       import f._