feat: add a Commit() helper that takes the Mutations directly (go…

…ogleapis/google-cloud-cpp-spanner#1319)

This convenience function saves the user from having to create a
small, but non-trivial lambda.

Fixes googleapis/google-cloud-cpp-spanner#1315.

google/cloud/spanner/client.cc

@@ -251,6 +251,10 @@ StatusOr<CommitResult> Client::Commit(
                 std::move(default_commit_backoff_policy));
 }
 
+StatusOr<CommitResult> Client::Commit(Mutations mutations) {
+  return Commit([&mutations](Transaction const&) { return mutations; });
+}
+
 StatusOr<CommitResult> Client::Commit(Transaction transaction,
                                       Mutations mutations) {
   return conn_->Commit({std::move(transaction), std::move(mutations)});

google/cloud/spanner/client.h

@@ -480,6 +480,14 @@ class Client {
   StatusOr<CommitResult> Commit(
       std::function<StatusOr<Mutations>(Transaction)> const& mutator);
 
+  /**
+   * Commits the given @p mutations atomically in order.
+   *
+   * This function uses the re-run loop described above with the default
+   * policies.
+   */
+  StatusOr<CommitResult> Commit(Mutations mutations);
+
   /**
    * Commits a read-write transaction.
    *

google/cloud/spanner/client_test.cc

@@ -684,6 +684,23 @@ TEST(ClientTest, CommitMutatorPermanentFailure) {
   EXPECT_EQ(1, commit_attempts);  // no reruns
 }
 
+TEST(ClientTest, CommitMutations) {
+  auto conn = std::make_shared<MockConnection>();
+  auto mutation = MakeDeleteMutation("table", KeySet::All());
+  auto timestamp = internal::TimestampFromRFC3339("2020-02-28T04:49:17.335Z");
+  ASSERT_STATUS_OK(timestamp);
+  EXPECT_CALL(*conn, Commit(_))
+      .WillOnce([&mutation, &timestamp](Connection::CommitParams const& cp) {
+        EXPECT_EQ(cp.mutations, Mutations{mutation});
+        return CommitResult{*timestamp};
+      });
+
+  Client client(conn);
+  auto result = client.Commit({mutation});
+  EXPECT_STATUS_OK(result);
+  EXPECT_EQ(*timestamp, result->commit_timestamp);
+}
+
 MATCHER(DoesNotHaveSession, "not bound to a session") {
   return internal::Visit(
       arg, [&](internal::SessionHolder& session,