close #2665 and close #2667: use weak conforman...

close #2665 and close #2667: use weak conformance in polymorphic case of
isApplicable reviewed by: odersky

exprTypeArgs now takes a comparison function: isWeaklyCompatible is    )
passed in isApplicable's typesCompatible (to mimic what happens in the )
monomorphic case Martin: please review as this is different from my    )
original proposal (that one broke type inference, this one passes all  )
tests and does not slow down quick.comp                                )

4 files changed, 17 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
index 712d469662..d11f263677 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
@@ -496,9 +496,9 @@ trait Infer {
      *  @param pt      ...
      *  @return        ...
      */
-    private def exprTypeArgs(tparams: List[Symbol], restpe: Type, pt: Type): List[Type] = {
+    private def exprTypeArgs(tparams: List[Symbol], restpe: Type, pt: Type, checkCompat: (Type, Type) => Boolean = isCompatible): List[Type] = {
       val tvars = tparams map freshVar
-      if (isCompatible(restpe.instantiateTypeParams(tparams, tvars), pt)) {
+      if (checkCompat(restpe.instantiateTypeParams(tparams, tvars), pt)) {
         try {
           // If the restpe is an implicit method, and the expected type is fully defined
           // optimze type varianbles wrt to the implicit formals only; ignore the result type.
@@ -788,7 +788,8 @@ trait Infer {
               try {
                 val uninstantiated = new ListBuffer[Symbol]
                 val targs = methTypeArgs(undetparams, formals, restpe, argtpes, pt, uninstantiated)
-                (exprTypeArgs(uninstantiated.toList, restpe.instantiateTypeParams(undetparams, targs), pt) ne null) &&
+                // #2665: must use weak conformance, not regular one (follow the monorphic case above)
+                (exprTypeArgs(uninstantiated.toList, restpe.instantiateTypeParams(undetparams, targs), pt, isWeaklyCompatible) ne null) &&
                 isWithinBounds(NoPrefix, NoSymbol, undetparams, targs)
               } catch {
                 case ex: NoInstance => false
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 1a8db1f27d..c3ca5d7e30 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2148,6 +2148,10 @@ trait Typers { self: Analyzer =>
         val pre = fun.symbol.tpe.prefix
 
         var sym = fun.symbol filter { alt =>
+          // must use pt as expected type, not WildcardType (a tempting quick fix to #2665)
+          // now fixed by using isWeaklyCompatible in exprTypeArgs
+          // TODO: understand why exactly -- some types were not inferred anymore (`ant clean quick.bin` failed)
+          // (I had expected inferMethodAlternative to pick up the slack introduced by using WildcardType here)
           isApplicableSafe(context.undetparams, followApply(pre.memberType(alt)), argtypes, pt)
         }
         if (sym hasFlag OVERLOADED) {
diff --git a/test/files/pos/t2665.scala b/test/files/pos/t2665.scala
new file mode 100644
index 0000000000..3163e31326
--- /dev/null
+++ b/test/files/pos/t2665.scala
@@ -0,0 +1,3 @@
+object Test {
+  val x: Unit = Array("")
+}
\ No newline at end of file
diff --git a/test/files/pos/t2667.scala b/test/files/pos/t2667.scala
new file mode 100644
index 0000000000..b214cc7f37
--- /dev/null
+++ b/test/files/pos/t2667.scala
@@ -0,0 +1,6 @@
+object A {
+  def foo(x: Int, y: Int*): Int = 45
+  def foo[T](x: T*): Int = 55
+
+  val x: Unit = foo(23, 23f)
+}
\ No newline at end of file