Realtime Pipeline Proto changes

Author: tom-andersen

firebase-firestore/src/proto/google/firebase/firestore/proto/target.proto

@@ -77,6 +77,9 @@ message Target {
 
     // A target specified by a set of document names.
     google.firestore.v1.Target.DocumentsTarget documents = 6;
+
+    // A target specified by a pipeline query.
+    google.firestore.v1.Target.PipelineQueryTarget pipeline_query = 13;
   }
 
   // Denotes the maximum snapshot version at which the associated query view

firebase-firestore/src/proto/google/firestore/v1/firestore.proto

@@ -866,13 +866,25 @@ message Target {
     }
   }
 
+  // A target specified by a pipeline query.
+  message PipelineQueryTarget {
+    // The pipeline to run.
+    oneof pipeline_type {
+      // A pipelined operation in structured format.
+      StructuredPipeline structured_pipeline = 1;
+    }
+  }
+
   // The type of target to listen to.
   oneof target_type {
     // A target specified by a query.
     QueryTarget query = 2;
 
     // A target specified by a set of document names.
     DocumentsTarget documents = 3;
+
+    // A target specified by a pipeline query.
+    PipelineQueryTarget pipeline_query = 13;
   }
 
   // When to start listening.

firebase-firestore/src/proto/google/firestore/v1/write.proto

@@ -200,6 +200,12 @@ message WriteResult {
 //
 // Multiple [DocumentChange][google.firestore.v1.DocumentChange] messages may be
 // returned for the same logical change, if multiple targets are affected.
+//
+// For PipelineQueryTargets, `document` will be in the new pipeline format,
+// (-- TODO(b/330735468): Insert link to spec. --)
+// For a Listen stream with both QueryTargets and PipelineQueryTargets present,
+// if a document matches both types of queries, then a separate DocumentChange
+// messages will be sent out one for each set.
 message DocumentChange {
   // The new state of the [Document][google.firestore.v1.Document].
   //