Implement the Any2StringAdd rewrite

input/src/main/scala/fix/scala213/Any2StringAdd.scala

@@ -0,0 +1,54 @@
+/*
+rule = fix.scala213.Any2StringAdd
+*/
+package fix.scala213
+
+abstract class Any2StringAdd {
+  // Strings: leave as-is, both literal strings and non-literal
+  def s = "bob"
+  def str1 = s + s
+  def str2 = s + "bob"
+  def str3 = "bob" + s
+  def str4 = "bob" + "fred"
+
+  // Non-strings: add toString
+  def nil = Nil + s
+
+  // Non-string, generic type: add toString
+  type A
+  def x: A
+  def generic = x + "bob"
+
+  // Primitives: add toString
+  def unit = ()
+  def bool = true
+  def byte = 1.toByte
+  def short = 1.toShort
+  def char = 'a'
+  def int = 1
+  def long = 1L
+  def float = 1.0F
+  def double = 1.0
+  //
+  def unit1 = unit + s
+  def bool1 = bool + s
+  def byte1 = byte + s
+  def byte2 = byte + byte
+  def short1 = short + s
+  def short2 = short + short
+  def char1 = char + s
+  def char2 = char + char
+  def int1 = int + s
+  def int2 = int + int
+  def long1 = long + s
+  def long2 = long + long
+  def float1 = float + s
+  def float2 = float + float
+  def double1 = double + s
+  def double2 = double + double
+
+  // With infix operators, make sure to use parens
+  def parens1 = Nil ++ Nil + s
+  def parens2 = int + int + s
+  def parens3 = {Nil ++ Nil} + s
+}

output/src/main/scala/fix/scala213/Any2StringAdd.scala

@@ -0,0 +1,51 @@
+package fix.scala213
+
+abstract class Any2StringAdd {
+  // Strings: leave as-is, both literal strings and non-literal
+  def s = "bob"
+  def str1 = s + s
+  def str2 = s + "bob"
+  def str3 = "bob" + s
+  def str4 = "bob" + "fred"
+
+  // Non-strings: add toString
+  def nil = Nil.toString + s
+
+  // Non-string, generic type: add toString
+  type A
+  def x: A
+  def generic = x.toString + "bob"
+
+  // Primitives: add toString
+  def unit = ()
+  def bool = true
+  def byte = 1.toByte
+  def short = 1.toShort
+  def char = 'a'
+  def int = 1
+  def long = 1L
+  def float = 1.0F
+  def double = 1.0
+  //
+  def unit1 = unit.toString + s
+  def bool1 = bool.toString + s
+  def byte1 = "" + byte + s
+  def byte2 = byte + byte
+  def short1 = "" + short + s
+  def short2 = short + short
+  def char1 = "" + char + s
+  def char2 = char + char
+  def int1 = "" + int + s
+  def int2 = int + int
+  def long1 = "" + long + s
+  def long2 = long + long
+  def float1 = "" + float + s
+  def float2 = float + float
+  def double1 = "" + double + s
+  def double2 = double + double
+
+  // With infix operators, make sure to use parens
+  def parens1 = (Nil ++ Nil).toString + s
+  def parens2 = "" + (int + int) + s
+  def parens3 = {Nil ++ Nil}.toString + s
+}

rewrites/src/main/resources/META-INF/services/scalafix.v1.Rule

@@ -1,3 +1,4 @@
+fix.scala213.Any2StringAdd
 fix.scala213.Core
 fix.scala213.ScalaSeq
 fix.scala213.Varargs

rewrites/src/main/scala/fix/scala213/Any2StringAdd.scala

@@ -0,0 +1,39 @@
+package fix.scala213
+
+import scalafix.v1._
+
+import scala.meta._
+
+object Any2StringAdd {
+  val any2stringaddPlusString = SymbolMatcher.exact("scala/Predef.any2stringadd#`+`().")
+  val primitivePlusString = SymbolMatcher.exact(
+    "scala/Byte#`+`().",
+    "scala/Short#`+`().",
+    "scala/Char#`+`().",
+    "scala/Int#`+`().",
+    "scala/Long#`+`().",
+    "scala/Float#`+`().",
+    "scala/Double#`+`().",
+  )
+}
+
+final class Any2StringAdd extends SemanticRule("fix.scala213.Any2StringAdd") {
+  import Any2StringAdd._
+
+  override def fix(implicit doc: SemanticDocument): Patch = {
+    doc.tree.collect {
+      case any2stringaddPlusString(Term.ApplyInfix(lhs, _, _, _)) => addToString(lhs)
+      case primitivePlusString(Term.ApplyInfix(lhs, _, _, _)) => blankStringPlus(lhs)
+    }.asPatch
+  }
+
+  private def addToString(term: Term) = term match {
+    case _: Term.Name | _: Term.Select | _: Term.Block => Patch.addRight(term, ".toString")
+    case _ => Patch.addLeft(term, "(") + Patch.addRight(term, ").toString")
+  }
+
+  private def blankStringPlus(term: Term) = term match {
+    case _: Term.Name | _: Term.Select | _: Term.Block => Patch.addLeft(term, """"" + """)
+    case _ => Patch.addLeft(term, """"" + (""") + Patch.addRight(term, ")")
+  }
+}