Initial Thrift definitions to support EdenFS filesystem notifications

Summary:
# Context

We are introducing EdenFS notifications to support scalable and ergonomic file system notifications for EdenFS mounts.

# This Diff

This diff introduces the initial Thrift definitions to support EdenFS filesystem notifications. It defines several new data structures and a single method `streamChangesSinceV2`.

# Technical Details

Simple-ish Thrift definitions that generate code, but are not used yet.

# Discussion Points

* There are two existing, simlar methods. One that has never been used as it was a hack-a-month project that was put on hold. The other is in use. The hack-a-month API, `streamSelectedChangesSince` could be removed now. The used method, `streamChangesSince` will need to remain until such time was we remove support for EdenFS mounts from Watchman.

Reviewed By: MichaelCuevas

Differential Revision: D65305161

fbshipit-source-id: 15a4b7cf89b37ebd1427193bfc06360006fa6bca

eden/fs/service/streamingeden.thrift

@@ -62,6 +62,54 @@ const i64 FS_EVENT_READ = 1;
 const i64 FS_EVENT_WRITE = 2;
 const i64 FS_EVENT_OTHER = 4;
 
+struct CommitTransition {
+  1: eden.ThriftRootId from;
+  2: eden.ThriftRootId to;
+}
+
+struct DirectoryRenamed {
+  1: eden.PathString from;
+  2: eden.PathString to;
+}
+
+struct Renamed {
+  1: eden.Dtype fileType;
+  2: eden.PathString from;
+  3: eden.PathString to;
+}
+
+struct Added {
+  1: eden.Dtype fileType;
+  3: eden.PathString path;
+}
+
+struct Deleted {
+  1: eden.Dtype fileType;
+  3: eden.PathString path;
+}
+
+struct Modified {
+  1: eden.Dtype fileType;
+  3: eden.PathString path;
+}
+
+union SmallChangeNotification {
+  1: Renamed renamed;
+  2: Added added;
+  3: Deleted deleted;
+  4: Modified modified;
+}
+
+union LargeChangeNotification {
+  1: DirectoryRenamed directoryRenamed;
+  2: CommitTransition commitTransition;
+}
+
+union ChangeNotification {
+  1: SmallChangeNotification smallChange;
+  2: LargeChangeNotification largeChange;
+}
+
 /**
  * The value of a stream item.
  *
@@ -82,6 +130,23 @@ struct ChangesSinceResult {
   1: eden.JournalPosition toPosition;
 }
 
+/**
+ * The value of a stream item in a streamChangedSinceV2 result stream.
+ *
+ * Each stream item refers to a single change notification
+ * since the notification clock provided.
+ */
+struct ChangeNotificationResult {
+  1: ChangeNotification change;
+}
+
+/**
+ * Return value of the streamChangedSinceV2 API
+ */
+struct ChangesSinceV2Result {
+  1: eden.JournalPosition toPosition;
+}
+
 /**
  * Argument to streamChangesSince API.
  */
@@ -98,6 +163,14 @@ struct StreamSelectedChangesSinceParams {
   2: list<string> globs;
 }
 
+/**
+ * Argument to streamChangedSinceV2 API
+ */
+struct StreamChangesSinceV2Params {
+  1: eden.PathString mountPoint;
+  2: eden.JournalPosition fromPosition;
+}
+
 struct TraceTaskEventsRequest {}
 
 typedef binary EdenStartStatusUpdate
@@ -196,6 +269,18 @@ service StreamingEdenService extends eden.EdenService {
     1: eden.EdenError ex,
   );
 
+  /**
+   * Returns a stream of change notifications for a given path since a specific point in time.
+   *
+   * This does not resolve expensive operations like moving a directory or changing
+   * commits. Callers must query Sapling to evaluate those potentially expensive operations.
+   */
+  ChangesSinceV2Result, stream<
+    ChangeNotificationResult throws (1: eden.EdenError ex)
+  > streamChangesSinceV2(1: StreamChangesSinceV2Params params) throws (
+    1: eden.EdenError ex,
+  );
+
   /**
    * Same as the API above but only returns files that match the globs in filter.
    * This API is intend to replace the above API but it's currently under development.