Fix Firestore when compiled with Xcode 8.3 (#1519)

* Add a travis stage that tests building Firestore with Xcode 8.3.

* Simulate on a device available in Xcode 8

* Fix compile errors under Xcode 8.3.3

* Remove Firestore_SwiftTests_iOS from the Firestore_Tests_iOS Scheme

I'll create a new target for this but in another PR.

* Add an entry to CHANGELOG.md

4 files changed, 8 insertions, 51 deletions

diff --git a/Firestore/CHANGELOG.md b/Firestore/CHANGELOG.md
index 8bb3e60..1703777 100644
--- a/Firestore/CHANGELOG.md
+++ b/Firestore/CHANGELOG.md
@@ -3,6 +3,7 @@
   atomically add and remove elements from an array field in a document.
 - [feature] Added `whereField(arrayContains:)` query filter to find
   documents where an array field contains a specific element.
+- [fixed] Fixed compilation with older Xcode versions (#1517).
 
 # v0.12.5
 - [changed] Internal improvements.
diff --git a/Firestore/Example/Firestore.xcodeproj/xcshareddata/xcschemes/Firestore_Tests_iOS.xcscheme b/Firestore/Example/Firestore.xcodeproj/xcshareddata/xcschemes/Firestore_Tests_iOS.xcscheme
index 03f30dc..69ebb9b 100644
--- a/Firestore/Example/Firestore.xcodeproj/xcshareddata/xcschemes/Firestore_Tests_iOS.xcscheme
+++ b/Firestore/Example/Firestore.xcodeproj/xcshareddata/xcschemes/Firestore_Tests_iOS.xcscheme
@@ -20,20 +20,6 @@
                ReferencedContainer = "container:Firestore.xcodeproj">
             </BuildableReference>
          </BuildActionEntry>
-         <BuildActionEntry
-            buildForTesting = "YES"
-            buildForRunning = "YES"
-            buildForProfiling = "YES"
-            buildForArchiving = "YES"
-            buildForAnalyzing = "YES">
-            <BuildableReference
-               BuildableIdentifier = "primary"
-               BlueprintIdentifier = "54C9EDF02040E16300A969CD"
-               BuildableName = "Firestore_SwiftTests_iOS.xctest"
-               BlueprintName = "Firestore_SwiftTests_iOS"
-               ReferencedContainer = "container:Firestore.xcodeproj">
-            </BuildableReference>
-         </BuildActionEntry>
       </BuildActionEntries>
    </BuildAction>
    <TestAction
@@ -52,16 +38,6 @@
                ReferencedContainer = "container:Firestore.xcodeproj">
             </BuildableReference>
          </TestableReference>
-         <TestableReference
-            skipped = "NO">
-            <BuildableReference
-               BuildableIdentifier = "primary"
-               BlueprintIdentifier = "54C9EDF02040E16300A969CD"
-               BuildableName = "Firestore_SwiftTests_iOS.xctest"
-               BlueprintName = "Firestore_SwiftTests_iOS"
-               ReferencedContainer = "container:Firestore.xcodeproj">
-            </BuildableReference>
-         </TestableReference>
       </Testables>
       <MacroExpansion>
          <BuildableReference
diff --git a/Firestore/core/src/firebase/firestore/local/local_serializer.cc b/Firestore/core/src/firebase/firestore/local/local_serializer.cc
index c549604..bdb2792 100644
--- a/Firestore/core/src/firebase/firestore/local/local_serializer.cc
+++ b/Firestore/core/src/firebase/firestore/local/local_serializer.cc
@@ -79,11 +79,7 @@ std::unique_ptr<model::MaybeDocument> LocalSerializer::DecodeMaybeDocument(
     Reader* reader) const {
   if (!reader->status().ok()) return nullptr;
 
-  // Initialize MaybeDocument fields to their default values. (Due to the
-  // 'oneof' in MaybeDocument, only one of 'no_document' or 'document' should
-  // ever be set.)
-  std::unique_ptr<model::NoDocument> no_document;
-  std::unique_ptr<model::Document> document;
+  std::unique_ptr<model::MaybeDocument> result;
 
   while (reader->bytes_left()) {
     Tag tag = reader->ReadTag();
@@ -94,33 +90,21 @@ std::unique_ptr<model::MaybeDocument> LocalSerializer::DecodeMaybeDocument(
       case firestore_client_MaybeDocument_document_tag:
         if (!reader->RequireWireType(PB_WT_STRING, tag)) return nullptr;
 
-        // 'no_document' and 'document' are part of a oneof. The proto docs
-        // claim that if both are set on the wire, the last one wins.
-        no_document = nullptr;
-
         // TODO(rsgowman): If multiple 'document' values are found, we should
         // merge them (rather than using the last one.)
-        document = reader->ReadNestedMessage<std::unique_ptr<model::Document>>(
+        result = reader->ReadNestedMessage<std::unique_ptr<model::Document>>(
             [&](Reader* reader) -> std::unique_ptr<model::Document> {
               return rpc_serializer_.DecodeDocument(reader);
             });
-
         break;
 
       case firestore_client_MaybeDocument_no_document_tag:
         if (!reader->RequireWireType(PB_WT_STRING, tag)) return nullptr;
 
-        // 'no_document' and 'document' are part of a oneof. The proto docs
-        // claim that if both are set on the wire, the last one wins.
-        document = nullptr;
-
         // TODO(rsgowman): If multiple 'no_document' values are found, we should
         // merge them (rather than using the last one.)
-        no_document =
-            reader->ReadNestedMessage<std::unique_ptr<model::NoDocument>>(
-                [&](Reader* reader) { return DecodeNoDocument(reader); });
-        break;
-
+        result = reader->ReadNestedMessage<std::unique_ptr<model::NoDocument>>(
+            [&](Reader* reader) { return DecodeNoDocument(reader); });
         break;
 
       default:
@@ -129,16 +113,12 @@ std::unique_ptr<model::MaybeDocument> LocalSerializer::DecodeMaybeDocument(
     }
   }
 
-  if (no_document) {
-    return no_document;
-  } else if (document) {
-    return document;
-  } else {
+  if (!result) {
     reader->set_status(Status(FirestoreErrorCode::DataLoss,
                               "Invalid MaybeDocument message: Neither "
                               "'no_document' nor 'document' fields set."));
-    return nullptr;
   }
+  return result;
 }
 
 void LocalSerializer::EncodeDocument(Writer* writer,
diff --git a/Firestore/core/test/firebase/firestore/remote/serializer_test.cc b/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
index fb08488..4e7b7c9 100644
--- a/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
+++ b/Firestore/core/test/firebase/firestore/remote/serializer_test.cc
@@ -161,7 +161,7 @@ class SerializerTest : public ::testing::Test {
     EXPECT_EQ(status.code(), bad_status.status().code());
   }
 
-  v1beta1::Value ValueProto(nullptr_t) {
+  v1beta1::Value ValueProto(std::nullptr_t) {
     std::vector<uint8_t> bytes =
         EncodeFieldValue(&serializer, FieldValue::NullValue());
     v1beta1::Value proto;