prohibits constructor overloading for macro bundles

As per Jason’s feedback, this commit handles overloaded constructors
in macro bundles. The backend now checks that we have a constructor of
a correct type. The frontend now prohibits multiple constructors altogether.

src/compiler/scala/reflect/macros/compiler/Errors.scala

@@ -51,7 +51,7 @@ trait Errors extends Traces {
 
   def MacroBundleNonStaticError() = bundleRefError("macro bundles must be static")
 
-  def MacroBundleWrongShapeError() = bundleRefError("macro bundles must be concrete classes having a single `val c: Context` parameter")
+  def MacroBundleWrongShapeError() = bundleRefError("macro bundles must be concrete classes having a single constructor with a `val c: Context` parameter")
 
   // compatibility errors
 

src/compiler/scala/reflect/macros/runtime/JavaReflectionRuntimes.scala

@@ -2,7 +2,9 @@ package scala.reflect.macros
 package runtime
 
 import scala.reflect.runtime.ReflectionUtils
-import scala.reflect.macros.blackbox.{Context => ApiContext}
+import scala.reflect.macros.blackbox.{Context => BlackboxContext}
+import scala.reflect.macros.whitebox.{Context => WhiteboxContext}
+import java.lang.reflect.{Constructor => jConstructor}
 
 trait JavaReflectionRuntimes {
   self: scala.tools.nsc.typechecker.Analyzer =>
@@ -19,8 +21,15 @@ trait JavaReflectionRuntimes {
       macroLogVerbose(s"successfully loaded macro impl as ($implClass, $implMeth)")
       args => {
         val implObj =
-          if (isBundle) implClass.getConstructors().head.newInstance(args.c)
-          else ReflectionUtils.staticSingletonInstance(implClass)
+          if (isBundle) {
+            def isMacroContext(clazz: Class[_]) = clazz == classOf[BlackboxContext] || clazz == classOf[WhiteboxContext]
+            def isBundleCtor(ctor: jConstructor[_]) = ctor.getParameterTypes match {
+              case Array(param) if isMacroContext(param) => true
+              case _ => false
+            }
+            val Array(bundleCtor) = implClass.getConstructors.filter(isBundleCtor)
+            bundleCtor.newInstance(args.c)
+          } else ReflectionUtils.staticSingletonInstance(implClass)
         val implArgs = if (isBundle) args.others else args.c +: args.others
         implMeth.invoke(implObj, implArgs.asInstanceOf[Seq[AnyRef]]: _*)
       }

src/reflect/scala/reflect/internal/Definitions.scala

@@ -616,8 +616,9 @@ trait Definitions extends api.StandardDefinitions {
 
     def isMacroBundleType(tp: Type) = {
       val isContextCompatible = macroBundleParamInfo(tp) != NoType
+      val hasSingleConstructor = !tp.declaration(nme.CONSTRUCTOR).isOverloaded
       val nonAbstract = !tp.erasure.typeSymbol.isAbstractClass
-      isContextCompatible && nonAbstract
+      isContextCompatible && hasSingleConstructor && nonAbstract
     }
 
     def isBlackboxMacroBundleType(tp: Type) =

test/files/neg/macro-bundle-abstract.check

@@ -1,4 +1,4 @@
-macro-bundle-abstract.scala:10: error: macro bundles must be concrete classes having a single `val c: Context` parameter
+macro-bundle-abstract.scala:10: error: macro bundles must be concrete classes having a single constructor with a `val c: Context` parameter
   def foo = macro Bundle.impl
                   ^
 one error found

test/files/neg/macro-bundle-overloaded.check

@@ -0,0 +1,4 @@
+macro-bundle-overloaded.scala:11: error: macro bundles must be concrete classes having a single constructor with a `val c: Context` parameter
+  def foo = macro Bundle.impl
+                  ^
+one error found

test/files/neg/macro-bundle-overloaded.scala

@@ -0,0 +1,12 @@
+import scala.language.experimental.macros
+import scala.reflect.macros.blackbox.{Context => BlackboxContext}
+import scala.reflect.macros.whitebox.{Context => WhiteboxContext}
+
+class Bundle(val c: BlackboxContext) {
+  def this(c: WhiteboxContext) = this(c: BlackboxContext)
+  def impl = ???
+}
+
+object Macros {
+  def foo = macro Bundle.impl
+}