[split] scrooge-generator: trim some allocations from generated scala…

… code

https://jira.twitter.biz/browse/HOSEBIRD-1550

This is a variety of small changes to the generated scala code
that removes some unnecessary object allocations.

RB_ID=262691

scrooge-generator/src/main/resources/scalagen/finagleClient.scala

@@ -1,11 +1,10 @@
 package {{package}}
 
-import com.twitter.finagle.SourcedException
+import com.twitter.finagle.{SourcedException, Service => FinagleService}
 import com.twitter.finagle.stats.{NullStatsReceiver, StatsReceiver}
 import com.twitter.finagle.thrift.ThriftClientRequest
-import com.twitter.finagle.{Service => FinagleService}
 import com.twitter.scrooge.{ThriftStruct, ThriftStructCodec}
-import com.twitter.util.Future
+import com.twitter.util.{Future, Return, Throw}
 import java.nio.ByteBuffer
 import java.util.Arrays
 import org.apache.thrift.protocol._
@@ -63,6 +62,17 @@ class {{ServiceName}}$FinagleClient(
     )
   }
 
+  protected def setServiceName(ex: Exception): Exception =
+    if (this.serviceName == "") ex
+    else {
+      ex match {
+        case se: SourcedException =>
+          se.serviceName = this.serviceName
+          se
+        case _ => ex
+      }
+    }
+
   // ----- end boilerplate.
 
 {{/hasParent}}

scrooge-generator/src/main/resources/scalagen/finagleClientFunction.scala

@@ -4,33 +4,41 @@ private[this] object {{__stats_name}} {
   val FailuresCounter = scopedStats.scope("{{clientFuncNameForWire}}").counter("failures")
   val FailuresScope = scopedStats.scope("{{clientFuncNameForWire}}").scope("failures")
 }
-
 {{#headerInfo}}{{>header}}{{/headerInfo}} = {
   {{__stats_name}}.RequestsCounter.incr()
   this.service(encodeRequest("{{clientFuncNameForWire}}", {{ArgsStruct}}({{argNames}}))) flatMap { response =>
     val result = decodeResponse(response, {{ResultStruct}})
-    val exception =
+    val exception: Future[Nothing] =
 {{#hasThrows}}
-      ({{#throws}}result.{{throwName}}{{/throws| orElse }}).map(Future.exception)
+      if (false)
+        null // can never happen, but needed to open a block
+{{#throws}}
+      else if (result.{{throwName}}.isDefined)
+        Future.exception(setServiceName(result.{{throwName}}.get))
+{{/throws}}
+      else
+        null
 {{/hasThrows}}
 {{^hasThrows}}
-      None
+      null
 {{/hasThrows}}
+
 {{#isVoid}}
-    exception.getOrElse(Future.Done)
+    if (exception != null) exception else Future.Done
 {{/isVoid}}
 {{^isVoid}}
-    exception.orElse(result.success.map(Future.value)).getOrElse(Future.exception(missingResult("{{clientFuncNameForWire}}")))
+    if (result.success.isDefined)
+      Future.value(result.success.get)
+    else if (exception != null)
+      exception
+    else
+      Future.exception(missingResult("{{clientFuncNameForWire}}"))
 {{/isVoid}}
-  } rescue {
-    case ex: SourcedException => {
-      if (this.serviceName != "") { ex.serviceName = this.serviceName }
-      Future.exception(ex)
-    }
-  } onSuccess { _ =>
-    {{__stats_name}}.SuccessCounter.incr()
-  } onFailure { ex =>
-    {{__stats_name}}.FailuresCounter.incr()
-    {{__stats_name}}.FailuresScope.counter(ex.getClass.getName).incr()
+  } respond {
+    case Return(_) =>
+      {{__stats_name}}.SuccessCounter.incr()
+    case Throw(ex) =>
+      {{__stats_name}}.FailuresCounter.incr()
+      {{__stats_name}}.FailuresScope.counter(ex.getClass.getName).incr()
   }
 }

scrooge-generator/src/main/resources/scalagen/finagleService.scala

@@ -64,11 +64,15 @@ class {{ServiceName}}$FinagleService(
 
     try {
       val msg = iprot.readMessageBegin()
-      functionMap.get(msg.name) map { _.apply(iprot, msg.seqid) } getOrElse {
-        TProtocolUtil.skip(iprot, TType.STRUCT)
-        exception(msg.name, msg.seqid, TApplicationException.UNKNOWN_METHOD,
-          "Invalid method name: '" + msg.name + "'")
-      }
+      val func = functionMap.get(msg.name)
+      func match {
+        case Some(fn) => 
+          fn(iprot, msg.seqid)
+        case _ =>
+          TProtocolUtil.skip(iprot, TType.STRUCT)
+          exception(msg.name, msg.seqid, TApplicationException.UNKNOWN_METHOD,
+            "Invalid method name: '" + msg.name + "'")
+      }      
     } catch {
       case e: Exception => Future.exception(e)
     }

scrooge-generator/src/main/resources/scalagen/service.scala

@@ -10,6 +10,7 @@ import org.apache.thrift.TApplicationException
 import org.apache.thrift.transport.TMemoryBuffer
 import scala.collection.immutable.{Map => immutable$Map}
 import scala.collection.mutable.{
+  Builder,
   ArrayBuffer => mutable$ArrayBuffer, Buffer => mutable$Buffer,
   HashMap => mutable$HashMap, HashSet => mutable$HashSet}
 import scala.collection.{Map, Set}

scrooge-generator/src/main/resources/scalagen/struct.scala

@@ -8,6 +8,7 @@ import org.apache.thrift.transport.{TMemoryBuffer, TTransport}
 import java.nio.ByteBuffer
 import java.util.Arrays
 import scala.collection.immutable.{Map => immutable$Map}
+import scala.collection.mutable.Builder
 import scala.collection.mutable.{
   ArrayBuffer => mutable$ArrayBuffer, Buffer => mutable$Buffer,
   HashMap => mutable$HashMap, HashSet => mutable$HashSet}
@@ -16,6 +17,7 @@ import scala.collection.{Map, Set}
 {{/public}}
 {{docstring}}
 object {{StructName}} extends ThriftStructCodec3[{{StructName}}] {
+  private val NoPassthroughFields = immutable$Map.empty[Short, TFieldBlob]
   val Struct = new TStruct("{{StructNameForWire}}")
 {{#fields}}
   val {{fieldConst}} = new TField("{{fieldNameForWire}}", TType.{{constType}}, {{id}})
@@ -54,7 +56,7 @@ object {{StructName}} extends ThriftStructCodec3[{{StructName}}] {
 {{/required}}
 {{/optional}}
 {{/fields}}
-    var _passthroughFields = immutable$Map.newBuilder[Short, TFieldBlob]
+    var _passthroughFields: Builder[(Short, TFieldBlob), immutable$Map[Short, TFieldBlob]] = null
     var _done = false
 
     _iprot.readStructBegin()
@@ -70,6 +72,8 @@ object {{StructName}} extends ThriftStructCodec3[{{StructName}}] {
             {{>readField}}
 {{/fields}}
           case _ =>
+            if (_passthroughFields == null)
+              _passthroughFields = immutable$Map.newBuilder[Short, TFieldBlob]
             _passthroughFields += (_field.id -> TFieldBlob.read(_field, _iprot))
             _readField = true
         }
@@ -90,7 +94,10 @@ object {{StructName}} extends ThriftStructCodec3[{{StructName}}] {
 {{#fields}}
       {{fieldName}},
 {{/fields}}
-      _passthroughFields.result()
+      if (_passthroughFields == null)
+        NoPassthroughFields
+      else
+        _passthroughFields.result()
     )
   }