Address comments.

Author: ehsannas

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

@@ -25,8 +25,6 @@
 /** @hide */
 @RestrictTo(RestrictTo.Scope.LIBRARY)
 public class Filter {
-  /** @hide */
-  @RestrictTo(RestrictTo.Scope.LIBRARY)
   static class FieldFilter extends Filter {
     private final FieldPath field;
     private final Operator operator;
@@ -52,8 +50,6 @@ public Object getValue() {
     }
   }
 
-  /** @hide */
-  @RestrictTo(RestrictTo.Scope.LIBRARY)
   static class CompositeFilter extends Filter {
     private final List<Filter> filters;
     private final StructuredQuery.CompositeFilter.Operator operator;

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

@@ -432,17 +432,15 @@ private FieldFilter parseFieldFilter(Filter.FieldFilter fieldFilterData) {
   }
 
   /**
-   * Takes a {@link Filter.CompositeFilter} object, parses each of its subfilters, and a new {@link
-   * CompositeFilter} that is constructed using the parsed values. Returns null if the given
-   * Filter.CompositeFilter does not contain any subfilters. Returns a {@link FieldFilter} if the
-   * given Filter.CompositeFilter contains only one field filter.
+   * Takes a {@link Filter.CompositeFilter} object, parses each of its subfilters, and returns a new
+   * {@link Filter} that is constructed using the parsed values.
    */
   private com.google.firebase.firestore.core.Filter parseCompositeFilter(
       Filter.CompositeFilter compositeFilterData) {
     List<com.google.firebase.firestore.core.Filter> parsedFilters = new ArrayList<>();
     for (Filter filter : compositeFilterData.getFilters()) {
       com.google.firebase.firestore.core.Filter parsedFilter = parseFilter(filter);
-      if (!parsedFilter.getFlattenedFilters().isEmpty()) {
+      if (!parsedFilter.getFilters().isEmpty()) {
         parsedFilters.add(parsedFilter);
       }
     }
@@ -472,7 +470,7 @@ private com.google.firebase.firestore.core.Filter parseFilter(Filter filter) {
   // TODO(orquery): This method will become public API. Change visibility and add documentation.
   private Query where(Filter filter) {
     com.google.firebase.firestore.core.Filter parsedFilter = parseFilter(filter);
-    if (parsedFilter.getFlattenedFilters().isEmpty()) {
+    if (parsedFilter.getFilters().isEmpty()) {
       // Return the existing query if not adding any more filters (e.g. an empty composite filter).
       return this;
     }
@@ -619,7 +617,7 @@ private void validateNewFieldFilter(
         validateOrderByFieldMatchesInequality(firstOrderByField, newInequality);
       }
     }
-    Operator conflictingOp = findFilterOperator(query.getFilters(), conflictingOps(filterOp));
+    Operator conflictingOp = findFilterWithOperator(query.getFilters(), conflictingOps(filterOp));
     if (conflictingOp != null) {
       // We special case when it's a duplicate op to give a slightly clearer error message.
       if (conflictingOp == filterOp) {
@@ -650,7 +648,7 @@ private void validateNewFilter(com.google.firebase.firestore.core.Filter filter)
    * returns the first one that is, or null if none are.
    */
   @Nullable
-  private Operator findFilterOperator(
+  private Operator findFilterWithOperator(
       List<com.google.firebase.firestore.core.Filter> filters, List<Operator> operators) {
     for (com.google.firebase.firestore.core.Filter filter : filters) {
       if (filter instanceof FieldFilter) {

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

@@ -33,6 +33,7 @@ public CompositeFilter(List<Filter> filters, Operator operator) {
     this.operator = operator;
   }
 
+  @Override
   public List<Filter> getFilters() {
     return filters;
   }

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

@@ -166,6 +166,12 @@ public List<FieldFilter> getFlattenedFilters() {
     return Collections.singletonList(this);
   }
 
+  @Override
+  public List<Filter> getFilters() {
+    // This is the only filter within this object, so we return a list of size one.
+    return Collections.singletonList(this);
+  }
+
   @Override
   public FieldPath getFirstInequalityField() {
     if (isInequality()) {

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

@@ -14,6 +14,7 @@
 
 package com.google.firebase.firestore.core;
 
+import androidx.annotation.Nullable;
 import com.google.firebase.firestore.model.Document;
 import com.google.firebase.firestore.model.FieldPath;
 import java.util.List;
@@ -28,6 +29,10 @@ public abstract class Filter {
   /** Returns a list of all field filters that are contained within this filter */
   public abstract List<FieldFilter> getFlattenedFilters();
 
+  /** Returns a list of all filters that are contained within this filter */
+  public abstract List<Filter> getFilters();
+
   /** Returns the field of the first filter that's an inequality, or null if none. */
+  @Nullable
   public abstract FieldPath getFirstInequalityField();
 }