Fix #7630: Use weak conformance in overloading resolution

Following the spec, use weak conformance when determining whether an
overloaded variant is applicable to arguments.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -666,7 +666,8 @@ trait Applications extends Compatibility {
    * argument trees.
    */
   class ApplicableToTreesDirectly(methRef: TermRef, targs: List[Type], args: List[Tree], resultType: Type)(implicit ctx: Context) extends ApplicableToTrees(methRef, targs, args, resultType)(ctx) {
-    override def argOK(arg: TypedArg, formal: Type): Boolean = argType(arg, formal) <:< formal.widenExpr
+    override def argOK(arg: TypedArg, formal: Type): Boolean =
+      argType(arg, formal) relaxed_<:< formal.widenExpr
   }
 
   /** Subclass of Application for applicability tests with value argument types. */

tests/run/i7630.check

@@ -0,0 +1 @@
+2

tests/run/i7630.scala

@@ -0,0 +1,19 @@
+object Asserts {
+  def assertEquals(expected: Any, actual: Any): Unit = {
+    println(1)
+    assert(expected.equals(actual), s"expected $expected but got $actual")
+  }
+
+  def assertEquals(expected: Long, actual: Long): Unit = {
+    println(2)
+    assert(expected == actual, s"expected $expected but got $actual")
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    def foo(): Long = 42L
+
+    Asserts.assertEquals(42, foo()) // an Int and a Long
+  }
+}