Unrevert "Fix bug in way function types are serialized to the Code Model."

This is a partial unrevert of "Fix bug in way function types are serialized
to the Code Model". The fix to CodeModelToPHP::visitTypeExpression() could
not be restored because the CodeModelToPHP class is not built into HHVM at
present.

Reviewed By: @ptarjan

Author: Herman Venter

hphp/compiler/type_annotation.cpp

@@ -189,8 +189,15 @@ void TypeAnnotation::outputCodeModel(CodeGenerator& cg) {
   auto numProps = 1;
   if (m_nullable) numProps++;
   if (m_soft) numProps++;
-  if (m_function) numProps++;
-  if (numTypeArgs > 0) numProps++;
+  if (m_function) {
+    numProps++;
+    // Since this is a function type, the first type argument is the return type
+    // and no typeArguments property will be serialized unless there are at
+    // least two type arguments.
+    if (numTypeArgs > 1) numProps++;
+  } else {
+    if (numTypeArgs > 0) numProps++;
+  }
   cg.printObjectHeader("TypeExpression", numProps);
   cg.printPropertyHeader("name");
   cg.printValue(m_tuple ? "tuple" : m_name);
@@ -206,6 +213,9 @@ void TypeAnnotation::outputCodeModel(CodeGenerator& cg) {
     cg.printPropertyHeader("returnType");
     typeArgsElem->outputCodeModel(cg);
     typeArgsElem = typeArgsElem->m_typeList;
+    // Since we've grabbed the first element of the list as the return
+    // type, make sure that the logic for serializing type arguments gets
+    // disabled unless there is at least one more type argument.
     numTypeArgs--;
   }
   if (numTypeArgs > 0) {