finagle-core: Add Address.ServiceFactory.apply Without Addr.Metadata

Problem

It's awkward ergonomically that `Address.apply` that takes a
`ServiceFactory` doesn't require `Addr.Metadata`, but the more specific
`Address.ServiceFactory.apply` does require `Addr.Metadata`. It's a rare
scenario where a user of the API would be supplying `Addr.Metadata` and
so it would be nicer if the `Address.ServiceFactory.apply` method did
not require it.

Solution

Add a variant of `Address.ServiceFactory.apply` which does not require
`Addr.Metadata` and defaults that value to `Addr.Metadata.empty`.

Differential Revision: https://phabricator.twitter.biz/D605438

CHANGELOG.rst

@@ -7,6 +7,12 @@ Note that ``PHAB_ID=#`` and ``RB_ID=#`` correspond to associated messages in com
 Unreleased
 ----------
 
+New Features
+~~~~~~~~~~~~
+
+* finagle-core: Added variant of `c.t.f.Address.ServiceFactory.apply` that does not require
+  specifying `c.t.f.Addr.Metadata` and defaults to `c.t.f.Addr.Metadata.empty`. ``PHAB_ID=D605438``
+
 21.1.0
 ------
 

finagle-core/src/main/scala/com/twitter/finagle/Address.scala

@@ -86,6 +86,12 @@ object Address {
     metadata: Addr.Metadata)
       extends Address
 
+  object ServiceFactory {
+    def apply[Req, Rep](
+      factory: com.twitter.finagle.ServiceFactory[Req, Rep]
+    ): ServiceFactory[Req, Rep] = ServiceFactory(factory, Addr.Metadata.empty)
+  }
+
   /** Create a new [[Address]] with given [[java.net.InetSocketAddress]]. */
   def apply(addr: InetSocketAddress): Address =
     Address.Inet(addr, Addr.Metadata.empty)

finagle-core/src/test/scala/com/twitter/finagle/AddressTest.scala

@@ -1,9 +1,23 @@
 package com.twitter.finagle
 
+import com.twitter.util.Future
 import java.net.{InetAddress, InetSocketAddress}
 import org.scalatest.FunSuite
 
 class AddressTest extends FunSuite {
+
+  def assertFactory[Req, Rep](address: Address, factory: ServiceFactory[Req, Rep]): Unit =
+    address match {
+      case Address.ServiceFactory(sf, _) => assert(sf == factory)
+      case _ => fail(s"$address is not an Address.ServiceFactory")
+    }
+
+  def assertMetadata(address: Address, metadata: Addr.Metadata): Unit =
+    address match {
+      case Address.ServiceFactory(_, md) => assert(md == metadata)
+      case _ => fail(s"$address is not an Address.ServiceFactory")
+    }
+
   test("constructor with no host points to localhost") {
     assert(Address(8080) == Address(new InetSocketAddress(InetAddress.getLoopbackAddress, 8080)))
   }
@@ -20,6 +34,26 @@ class AddressTest extends FunSuite {
     val cmp12 = ordering.compare(sorted(0), sorted(1))
     val cmp23 = ordering.compare(sorted(1), sorted(2))
     assert(cmp13 == 0 && cmp12 == 0 && cmp23 == 0 || cmp13 < 0 && (cmp12 < 0 || cmp23 < 0))
+  }
+
+  test("can be created via a ServiceFactory") {
+    val service: Service[String, String] = Service.mk(_ => Future.value("Whatever"))
+    val sf: ServiceFactory[String, String] = ServiceFactory.const(service)
+
+    // Without Metadata
+    val address1: Address = Address.ServiceFactory(sf)
+    assertFactory(address1, sf)
+    assertMetadata(address1, Addr.Metadata.empty)
+
+    // With Metadata
+    val metadata = Addr.Metadata("a" -> "b")
+    val address2: Address = Address.ServiceFactory(sf, metadata)
+    assertFactory(address2, sf)
+    assertMetadata(address2, metadata)
 
+    // Without Metadata via Address.apply
+    val address3: Address = Address(sf)
+    assertFactory(address3, sf)
+    assertMetadata(address3, Addr.Metadata.empty)
   }
 }