CR Feedback.

Author: Michael Lehenbauer

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -236,8 +236,8 @@ public DocumentReference document(@NonNull String documentPath) {
   }
 
   /**
-   * Creates and returns a new Query that includes all documents in the database that are contained
-   * in a collection or subcollection with the given collectionId.
+   * Creates and returns a new @link{Query} that includes all documents in the database that are
+   * contained in a collection or subcollection with the given @code{collectionId}.
    *
    * @param collectionId Identifies the collections to query over. Every collection or subcollection
    *     with this ID as the last segment of its path will be included. Cannot contain a slash.
@@ -252,6 +252,7 @@ public Query collectionGroup(@NonNull String collectionId) {
           String.format(
               "Invalid collectionId '%s'. Collection IDs must not contain '/'.", collectionId));
     }
+
     ensureClientConfigured();
     return new Query(
         new com.google.firebase.firestore.core.Query(ResourcePath.EMPTY, collectionId), this);

firebase-firestore/src/main/java/com/google/firebase/firestore/Query.java

@@ -329,14 +329,14 @@ private Query whereHelper(@NonNull FieldPath fieldPath, Operator op, Object valu
               "Invalid query. When querying with FieldPath.documentId() you must provide a valid "
                   + "document ID, but it was an empty string.");
         }
-        if (!this.query.isCollectionGroupQuery() && documentKey.contains("/")) {
+        if (!query.isCollectionGroupQuery() && documentKey.contains("/")) {
           throw new IllegalArgumentException(
               "Invalid query. When querying a collection by FieldPath.documentId() you must "
                   + "provide a plain document ID, but '"
                   + documentKey
                   + "' contains a '/' character.");
         }
-        ResourcePath path = this.query.getPath().append(ResourcePath.fromString(documentKey));
+        ResourcePath path = query.getPath().append(ResourcePath.fromString(documentKey));
         if (!DocumentKey.isDocumentKey(path)) {
           throw new IllegalArgumentException(
               "Invalid query. When querying a collection group by FieldPath.documentId(), the "
@@ -663,7 +663,7 @@ private Bound boundFromFields(String methodName, Object[] values, boolean before
                   + ".");
         }
         String documentId = (String) rawValue;
-        if (!this.query.isCollectionGroupQuery() && documentId.contains("/")) {
+        if (!query.isCollectionGroupQuery() && documentId.contains("/")) {
           throw new IllegalArgumentException(
               "Invalid query. When querying a collection and ordering by FieldPath.documentId(), "
                   + "the value passed to "

firebase-firestore/src/main/java/com/google/firebase/firestore/core/Query.java

@@ -111,7 +111,7 @@ public boolean isDocumentQuery() {
 
   /** Returns true if this is a collection group query. */
   public boolean isCollectionGroupQuery() {
-    return this.collectionGroup != null;
+    return collectionGroup != null;
   }
 
   /** The filters on the documents returned by the query. */

firebase-firestore/src/main/java/com/google/firebase/firestore/local/IndexManager.java

@@ -28,6 +28,9 @@ public interface IndexManager {
    * Creates an index entry mapping the collectionId (last segment of the path) to the parent path
    * (either the containing document location or the empty path for root-level collections). Index
    * entries can be retrieved via getCollectionParents().
+   *
+   * <p>NOTE: Currently we don't remove index entries. If this ends up being an issue we can devise
+   * some sort of GC strategy.
    */
   void addToCollectionParentIndex(ResourcePath collectionPath);
 

firebase-firestore/src/main/java/com/google/firebase/firestore/local/MemoryIndexManager.java

@@ -44,14 +44,15 @@ public List<ResourcePath> getCollectionParents(String collectionId) {
 
   /**
    * Internal implementation of the collection-parent index. Also used for in-memory caching by
-   * SQLiteIndexManager and initial index population in SQLiteSchema.java
+   * SQLiteIndexManager and initial index population in SQLiteSchema.
    */
   static class MemoryCollectionParentIndex {
     private final HashMap<String, HashSet<ResourcePath>> index = new HashMap<>();
 
     // Returns false if the entry already existed.
     boolean add(ResourcePath collectionPath) {
       hardAssert(collectionPath.length() % 2 == 1, "Expected a collection path.");
+
       String collectionId = collectionPath.getLastSegment();
       ResourcePath parentPath = collectionPath.popLast();
       HashSet<ResourcePath> existingParents = index.get(collectionId);

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteIndexManager.java

@@ -41,8 +41,8 @@ final class SQLiteIndexManager implements IndexManager {
   @Override
   public void addToCollectionParentIndex(ResourcePath collectionPath) {
     hardAssert(collectionPath.length() % 2 == 1, "Expected a collection path.");
+
     if (collectionParentsCache.add(collectionPath)) {
-      hardAssert(collectionPath.length() >= 1, "Invalid collection path.");
       String collectionId = collectionPath.getLastSegment();
       ResourcePath parentPath = collectionPath.popLast();
       db.execute(