Misc indexing fixes

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

@@ -160,7 +160,7 @@ private List<FieldFilter> getFieldFiltersForPath(FieldPath path) {
           case EQUAL:
           case IN:
             // Encode equality prefix, which is encoded in the index value before the inequality
-            // (e.g. `a == 'a' && b != 'b' is encoded to 'value != ab').
+            // (e.g. `a == 'a' && b != 'b'` is encoded to `value != 'ab'`).
             values.add(fieldFilter.getValue());
             break;
           case NOT_IN:
@@ -338,10 +338,6 @@ public Bound getLowerBound(FieldIndex fieldIndex) {
       inclusive &= segmentInclusive;
     }
 
-    if (values.isEmpty()) {
-      return null;
-    }
-
     return new Bound(values, inclusive);
   }
 

firebase-firestore/src/main/java/com/google/firebase/firestore/model/Values.java

@@ -500,9 +500,7 @@ public static Value getLowerBound(Value.ValueTypeCase valueTypeCase) {
     }
   }
 
-  /**
-   * Returns the largest value for the given value type (exclusive). Returns {@code null} for maps.
-   */
+  /** Returns the largest value for the given value type (exclusive). */
   public static Value getUpperBound(Value.ValueTypeCase valueTypeCase) {
     switch (valueTypeCase) {
       case NULL_VALUE:

firebase-firestore/src/test/java/com/google/firebase/firestore/core/TargetTest.java

@@ -49,7 +49,7 @@ public void emptyQueryBound() {
     verifyBound(lowerBound, true);
 
     Bound upperBound = target.getUpperBound(index);
-    assertNull(upperBound);
+    verifyBound(upperBound, true);
   }
 
   @Test
@@ -65,7 +65,7 @@ public void equalsQueryBound() {
   }
 
   @Test
-  public void lowerThanQueryBound() {
+  public void lessThanQueryBound() {
     Target target = query("c").filter(filter("foo", "<", "bar")).toTarget();
     FieldIndex index = fieldIndex("c", "foo", FieldIndex.Segment.Kind.DESCENDING);
 
@@ -77,7 +77,7 @@ public void lowerThanQueryBound() {
   }
 
   @Test
-  public void lowerThanOrEqualsQueryBound() {
+  public void lessThanOrEqualsQueryBound() {
     Target target = query("c").filter(filter("foo", "<=", "bar")).toTarget();
     FieldIndex index = fieldIndex("c", "foo", FieldIndex.Segment.Kind.ASCENDING);
 
@@ -124,7 +124,7 @@ public void arrayContainsQueryBound() {
     verifyBound(lowerBound, true);
 
     Bound upperBound = target.getUpperBound(index);
-    assertNull(upperBound);
+    verifyBound(upperBound, true);
   }
 
   @Test
@@ -142,7 +142,7 @@ public void arrayContainsAnyQueryBound() {
     verifyBound(lowerBound, true);
 
     Bound upperBound = target.getUpperBound(index);
-    assertNull(upperBound);
+    verifyBound(upperBound, true);
   }
 
   @Test

firebase-firestore/src/test/java/com/google/firebase/firestore/local/SQLiteIndexManagerTest.java

@@ -124,6 +124,22 @@ public void testNotEqualsFilter() {
     verifyResults(query, "coll/val1", "coll/val3");
   }
 
+  @Test
+  public void testEqualsWithNotEqualsFilter() {
+    indexManager.addFieldIndex(fieldIndex("coll", "a", Kind.ASCENDING, "b", Kind.ASCENDING));
+    addDoc("coll/val1", map("a", 1, "b", 1));
+    addDoc("coll/val2", map("a", 1, "b", 2));
+    addDoc("coll/val3", map("a", 2, "b", 1));
+    addDoc("coll/val4", map("a", 2, "b", 2));
+
+    // Verifies that we apply the filter in the order of the field index
+    Query query = query("coll").filter(filter("a", "==", 1)).filter(filter("b", "!=", 1));
+    verifyResults(query, "coll/val2");
+
+    query = query("coll").filter(filter("b", "!=", 1)).filter(filter("a", "==", 1));
+    verifyResults(query, "coll/val2");
+  }
+
   @Test
   public void testLessThanFilter() {
     setUpSingleValueFilter();

firebase-firestore/src/test/java/com/google/firebase/firestore/model/ValuesTest.java

@@ -254,7 +254,7 @@ public void testLowerBound() {
   }
 
   @Test
-  public void testNextValue() {
+  public void testUpperBound() {
     new ComparatorTester()
         // null first
         .addEqualityGroup(wrap((Object) null))