Allow implicit conversion Predef.any2stringadd with -migration

With -migration the implicit conversion will be used and the user will see the deprecation warning.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -347,19 +347,21 @@ class Definitions {
 
   @tu lazy val ScalaPredefModule: Symbol = {
     val mod = ctx.requiredModule("scala.Predef")
-    mod.infoOrCompleter match {
-      case completer: ModuleCompleter =>
-        mod.info = new ModuleCompleter(completer.moduleClass) {
-          override def complete(root: SymDenotation)(implicit ctx: Context): Unit = {
-            super.complete(root)
-            // Disable the implicit conversion any2stringadd we remove the `implicit` moifier.
-            // Using it explicitly will emit the usual deprection warining.
-            val meth = root.requiredMethod("any2stringadd")
-            meth.resetFlag(Implicit)
+    if (!ctx.settings.migration.value) {
+      mod.infoOrCompleter match {
+        case completer: ModuleCompleter =>
+          mod.info = new ModuleCompleter(completer.moduleClass) {
+            override def complete(root: SymDenotation)(implicit ctx: Context): Unit = {
+              super.complete(root)
+              // Disable the implicit conversion any2stringadd we remove the `implicit` moifier.
+              // Using it explicitly will emit the usual deprection warining.
+              val meth = root.requiredMethod("any2stringadd")
+              meth.resetFlag(Implicit)
+            }
           }
-        }
-      case _ =>
+        case _ =>
         // Compiling Predef from source
+      }
     }
     mod
   }

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -47,6 +47,7 @@ class CompilationTests extends ParallelTesting {
       compileFilesInDir("tests/pos-special/spec-t5545", defaultOptions),
       compileFilesInDir("tests/pos-special/strawman-collections", defaultOptions),
       compileFilesInDir("tests/pos-special/isInstanceOf", allowDeepSubtypes.and("-Xfatal-warnings")),
+      compileFile("tests/pos-special/i7137.scala", defaultOptions.and("-migration")),
       compileFilesInDir("tests/new", defaultOptions),
       compileFilesInDir("tests/pos-scala2", scala2Mode),
       compileFilesInDir("tests/pos", defaultOptions),

tests/pos-special/i7137.scala

@@ -0,0 +1,7 @@
+
+object App {
+  val any: Any = 3
+  val str: String = any + "a" // allowed with -migration
+  val str2: String = any2stringadd(any) + "a"
+  val str3: String = Predef.any2stringadd(any) + "a"
+}