Add lint checking for Objective-C++ sources (#1048)

* lint.sh now lints Objective-C++ too

* cpplint checks system-style includes that should be user-style

This prevents it from recognizing project sources as if they were C
system headers and then complaining that they're in the wrong place.

* cpplint checks #imports and #includes

* cpplint checks that C++ system headers aren't #imported

* cpplint checks for C system headers that could be C++ system headers

* cpplint checks that Objective-C sources include their headers

10 files changed, 37 insertions, 19 deletions

diff --git a/Firestore/Source/Local/FSTLevelDB.mm b/Firestore/Source/Local/FSTLevelDB.mm
index 4812228..fae85e7 100644
--- a/Firestore/Source/Local/FSTLevelDB.mm
+++ b/Firestore/Source/Local/FSTLevelDB.mm
@@ -16,7 +16,7 @@
 
 #import "Firestore/Source/Local/FSTLevelDB.h"
 
-#include <leveldb/db.h>
+#include <memory>
 
 #import "FIRFirestoreErrors.h"
 #import "Firestore/Source/Local/FSTLevelDBMigrations.h"
@@ -26,13 +26,14 @@
 #import "Firestore/Source/Remote/FSTSerializerBeta.h"
 #import "Firestore/Source/Util/FSTAssert.h"
 #import "Firestore/Source/Util/FSTLogger.h"
-#include "absl/memory/memory.h"
 
 #include "Firestore/core/src/firebase/firestore/auth/user.h"
 #include "Firestore/core/src/firebase/firestore/core/database_info.h"
 #include "Firestore/core/src/firebase/firestore/local/leveldb_transaction.h"
 #include "Firestore/core/src/firebase/firestore/model/database_id.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
+#include "absl/memory/memory.h"
+#include "leveldb/db.h"
 
 namespace util = firebase::firestore::util;
 using firebase::firestore::auth::User;
diff --git a/Firestore/Source/Local/FSTLevelDBKey.h b/Firestore/Source/Local/FSTLevelDBKey.h
index c7a64ee..5b234ec 100644
--- a/Firestore/Source/Local/FSTLevelDBKey.h
+++ b/Firestore/Source/Local/FSTLevelDBKey.h
@@ -16,6 +16,8 @@
 
 #import <Foundation/Foundation.h>
 
+#include <string>
+
 #import "Firestore/Source/Core/FSTTypes.h"
 #import "Firestore/Source/Local/StringView.h"
 
diff --git a/Firestore/Source/Local/FSTLevelDBMigrations.mm b/Firestore/Source/Local/FSTLevelDBMigrations.mm
index cf06c9f..fefd0f7 100644
--- a/Firestore/Source/Local/FSTLevelDBMigrations.mm
+++ b/Firestore/Source/Local/FSTLevelDBMigrations.mm
@@ -14,16 +14,18 @@
  * limitations under the License.
  */
 
-#include "Firestore/Source/Local/FSTLevelDBMigrations.h"
+#import "Firestore/Source/Local/FSTLevelDBMigrations.h"
 
-#include <absl/strings/match.h>
-#include "leveldb/write_batch.h"
+#include <string>
 
 #import "Firestore/Protos/objc/firestore/local/Target.pbobjc.h"
 #import "Firestore/Source/Local/FSTLevelDBKey.h"
 #import "Firestore/Source/Local/FSTLevelDBQueryCache.h"
 #import "Firestore/Source/Util/FSTAssert.h"
 
+#include "absl/strings/match.h"
+#include "leveldb/write_batch.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
 // Current version of the schema defined in this file.
diff --git a/Firestore/Source/Local/FSTLevelDBMutationQueue.mm b/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
index 29acead..75c3cf6 100644
--- a/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
+++ b/Firestore/Source/Local/FSTLevelDBMutationQueue.mm
@@ -16,13 +16,10 @@
 
 #import "Firestore/Source/Local/FSTLevelDBMutationQueue.h"
 
+#include <memory>
 #include <set>
 #include <string>
 
-#include <absl/strings/match.h>
-#include <leveldb/db.h>
-#include <leveldb/write_batch.h>
-
 #import "Firestore/Protos/objc/firestore/local/Mutation.pbobjc.h"
 #import "Firestore/Source/Core/FSTQuery.h"
 #import "Firestore/Source/Local/FSTLevelDB.h"
@@ -38,6 +35,9 @@
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
 #include "Firestore/core/src/firebase/firestore/util/string_util.h"
+#include "absl/strings/match.h"
+#include "leveldb/db.h"
+#include "leveldb/write_batch.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
diff --git a/Firestore/Source/Local/FSTLevelDBQueryCache.mm b/Firestore/Source/Local/FSTLevelDBQueryCache.mm
index aa1ab41..5fde7d7 100644
--- a/Firestore/Source/Local/FSTLevelDBQueryCache.mm
+++ b/Firestore/Source/Local/FSTLevelDBQueryCache.mm
@@ -16,6 +16,9 @@
 
 #import "Firestore/Source/Local/FSTLevelDBQueryCache.h"
 
+#include <memory>
+#include <string>
+
 #import "Firestore/Protos/objc/firestore/local/Target.pbobjc.h"
 #import "Firestore/Source/Core/FSTQuery.h"
 #import "Firestore/Source/Local/FSTLevelDB.h"
@@ -23,9 +26,9 @@
 #import "Firestore/Source/Local/FSTLocalSerializer.h"
 #import "Firestore/Source/Local/FSTQueryData.h"
 #import "Firestore/Source/Util/FSTAssert.h"
-#include "absl/strings/match.h"
 
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
+#include "absl/strings/match.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
diff --git a/Firestore/Source/Local/FSTLevelDBRemoteDocumentCache.mm b/Firestore/Source/Local/FSTLevelDBRemoteDocumentCache.mm
index 703fc69..f655e3a 100644
--- a/Firestore/Source/Local/FSTLevelDBRemoteDocumentCache.mm
+++ b/Firestore/Source/Local/FSTLevelDBRemoteDocumentCache.mm
@@ -16,8 +16,6 @@
 
 #import "Firestore/Source/Local/FSTLevelDBRemoteDocumentCache.h"
 
-#include <leveldb/db.h>
-#include <leveldb/write_batch.h>
 #include <string>
 
 #import "Firestore/Protos/objc/firestore/local/MaybeDocument.pbobjc.h"
@@ -29,8 +27,11 @@
 #import "Firestore/Source/Model/FSTDocumentDictionary.h"
 #import "Firestore/Source/Model/FSTDocumentSet.h"
 #import "Firestore/Source/Util/FSTAssert.h"
+
 #include "Firestore/core/src/firebase/firestore/local/leveldb_transaction.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
+#include "leveldb/db.h"
+#include "leveldb/write_batch.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
diff --git a/Firestore/Source/Local/FSTLocalSerializer.mm b/Firestore/Source/Local/FSTLocalSerializer.mm
index 1d9455d..61e173a 100644
--- a/Firestore/Source/Local/FSTLocalSerializer.mm
+++ b/Firestore/Source/Local/FSTLocalSerializer.mm
@@ -16,7 +16,7 @@
 
 #import "Firestore/Source/Local/FSTLocalSerializer.h"
 
-#include <inttypes.h>
+#include <cinttypes>
 
 #import "Firestore/Protos/objc/firestore/local/MaybeDocument.pbobjc.h"
 #import "Firestore/Protos/objc/firestore/local/Mutation.pbobjc.h"
diff --git a/Firestore/Source/Local/FSTLocalStore.mm b/Firestore/Source/Local/FSTLocalStore.mm
index 990e332..b5dfeec 100644
--- a/Firestore/Source/Local/FSTLocalStore.mm
+++ b/Firestore/Source/Local/FSTLocalStore.mm
@@ -16,6 +16,8 @@
 
 #import "Firestore/Source/Local/FSTLocalStore.h"
 
+#include <set>
+
 #import "FIRTimestamp.h"
 #import "Firestore/Source/Core/FSTListenSequence.h"
 #import "Firestore/Source/Core/FSTQuery.h"
diff --git a/Firestore/Source/Local/FSTNoOpGarbageCollector.mm b/Firestore/Source/Local/FSTNoOpGarbageCollector.mm
index 451cde2..421d283 100644
--- a/Firestore/Source/Local/FSTNoOpGarbageCollector.mm
+++ b/Firestore/Source/Local/FSTNoOpGarbageCollector.mm
@@ -16,6 +16,8 @@
 
 #import "Firestore/Source/Local/FSTNoOpGarbageCollector.h"
 
+#include <set>
+
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 
 using firebase::firestore::model::DocumentKey;
diff --git a/Firestore/Source/Local/StringView.h b/Firestore/Source/Local/StringView.h
index 4e36cff..85afcaa 100644
--- a/Firestore/Source/Local/StringView.h
+++ b/Firestore/Source/Local/StringView.h
@@ -19,9 +19,10 @@
 
 #import <Foundation/Foundation.h>
 
-#include <leveldb/slice.h>
 #include <string>
+
 #include "absl/strings/string_view.h"
+#include "leveldb/slice.h"
 
 namespace Firestore {
 
@@ -43,7 +44,7 @@ class StringView {
   // Creates a StringView from an NSString. When StringView is an argument type
   // into which an NSString* is passed, the caller should ensure that the
   // NSString is retained.
-  StringView(NSString *str)
+  StringView(NSString *str)  // NOLINT(runtime/explicit)
       : data_([str UTF8String]), size_([str lengthOfBytesUsingEncoding:NSUTF8StringEncoding]) {
   }
 
@@ -54,20 +55,24 @@ class StringView {
 
   // Creates a StringView from the given char* pointer but computes the size
   // with strlen. This is really only suitable for passing C string literals.
-  StringView(const char *data) : data_(data), size_(strlen(data)) {
+  StringView(const char *data)  // NOLINT(runtime/explicit)
+      : data_(data), size_(strlen(data)) {
   }
 
   // Creates a StringView from the given slice.
-  StringView(leveldb::Slice slice) : data_(slice.data()), size_(slice.size()) {
+  StringView(leveldb::Slice slice)  // NOLINT(runtime/explicit)
+      : data_(slice.data()), size_(slice.size()) {
   }
 
   // Creates a StringView from the absl::string_view.
-  StringView(absl::string_view s) : data_(s.data()), size_(s.size()) {
+  StringView(absl::string_view s)  // NOLINT(runtime/explicit)
+      : data_(s.data()), size_(s.size()) {
   }
 
   // Creates a StringView from the given std::string. The string must be an
   // lvalue for the lifetime requirements to be satisfied.
-  StringView(const std::string &str) : data_(str.data()), size_(str.size()) {
+  StringView(const std::string &str)  // NOLINT(runtime/explicit)
+      : data_(str.data()), size_(str.size()) {
   }
 
   // Converts this StringView to a Slice, which is an equivalent (and more