Fix comments from Internal review (#2935)

* Fix comments from Internal review

* Updates from Copybara

This PR addresses comments from cl/392912920

Author: schmidt-sebastian

firebase-firestore/firebase-firestore.gradle

@@ -155,7 +155,7 @@ dependencies {
     }
 
     compileOnly 'com.google.auto.value:auto-value-annotations:1.6.6'
-    androidTestAnnotationProcessor 'com.google.auto.value:auto-value:1.6.5'
+    annotationProcessor 'com.google.auto.value:auto-value:1.6.5'
 
     testImplementation 'junit:junit:4.12'
     testImplementation 'androidx.test:core:1.2.0'

firebase-firestore/src/main/java/com/google/firebase/firestore/index/FirestoreIndexValueWriter.java

@@ -22,16 +22,14 @@
 import com.google.type.LatLng;
 import java.util.Map;
 
-/**
- * Firestore index value writer.
- *
- * <p>See the <a
- * href="https://g3doc.corp.google.com/cloud/datastore/g3doc/architecture/spanner/storage_format.md">storage
- * format design</a> for details.
- */
+/** Firestore index value writer. */
 public class FirestoreIndexValueWriter {
   // Note: This code is copied from the backend. Code that is not used by Firestore was removed.
 
+  // The client SDK only supports references to documents from the same database. We can skip the
+  // first five segments.
+  public static final int DOCUMENT_NAME_OFFSET = 5;
+
   public static final int INDEX_TYPE_NULL = 5;
   public static final int INDEX_TYPE_BOOLEAN = 10;
   public static final int INDEX_TYPE_NAN = 13;
@@ -155,7 +153,7 @@ private void writeIndexEntityRef(String referenceValue, DirectionalIndexByteEnco
     ResourcePath path = ResourcePath.fromString(referenceValue);
 
     int numSegments = path.length();
-    for (int index = 6; index < numSegments; ++index) {
+    for (int index = DOCUMENT_NAME_OFFSET; index < numSegments; ++index) {
       String segment = path.getSegment(index);
 
       writeValueTypeLabel(encoder, INDEX_TYPE_REFERENCE_SEGMENT);

firebase-firestore/src/main/java/com/google/firebase/firestore/index/OrderedCodeReader.java

@@ -26,8 +26,8 @@
 import static java.lang.Character.MIN_SURROGATE;
 
 /**
- * OrderedCodeReader is a minimal-allocation implementation of the reading behavior defined by
- * {@link com.google.bigtable.util.OrderedCode}.
+ * OrderedCodeReader is a minimal-allocation implementation of the reading behavior defined by our
+ * backend.
  *
  * <p>This class will throw {@link IllegalArgumentException} on invalid input.
  */

firebase-firestore/src/main/java/com/google/firebase/firestore/index/OrderedCodeWriter.java

@@ -22,8 +22,8 @@
 import java.util.Arrays;
 
 /**
- * OrderedCodeWriter is a minimal-allocation implmentation of the writing behavior defined by {@link
- * com.google.bigtable.util.OrderedCode}.
+ * OrderedCodeWriter is a minimal-allocation implmentation of the writing behavior defined by the
+ * backend.
  */
 public class OrderedCodeWriter {
   // Note: This code is copied from the backend. Code that is not used by Firestore was removed.
@@ -36,11 +36,7 @@ public class OrderedCodeWriter {
   public static final byte INFINITY = (byte) 0xff; // Combined with ESCAPE2
   public static final byte FF_BYTE = 0x00; // Combined with ESCAPE2
 
-  /**
-   * These constants are based on {@link
-   * com.google.storage.megastore.metadata.adapters.DoubleAdapter}, see
-   * OrderedCodeWriter::writeDoubleAscending for details.
-   */
+  /** These constants are taken from the backend. */
   public static final long DOUBLE_SIGN_MASK = 0x8000000000000000L;
 
   public static final long DOUBLE_ALL_BITS = 0xFFFFFFFFFFFFFFFFL;
@@ -225,7 +221,6 @@ public void writeSignedLongDescending(long value) {
   }
 
   public void writeDoubleAscending(double val) {
-    // Based on com.google.storage.megastore.metadata.adapters.DoubleAdapter.
     // This particular encoding has the following properties:
     // The order matches the IEEE 754 floating-point comparison results with the
     // following exceptions:

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

@@ -15,6 +15,7 @@
 package com.google.firebase.firestore.model;
 
 import androidx.annotation.NonNull;
+import com.google.auto.value.AutoValue;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
@@ -33,7 +34,8 @@
 public final class FieldIndex implements Iterable<FieldIndex.Segment> {
 
   /** An index component consisting of field path and index type. */
-  public static final class Segment {
+  @AutoValue
+  public abstract static class Segment {
     /** The type of the index, e.g. for which type of query it can be used. */
     public enum Kind {
       /** Ascending index. Can be used for <, <=, ==, >=, >, !=, IN and NOT IN queries. */
@@ -42,44 +44,15 @@ public enum Kind {
       CONTAINS
     }
 
-    private final FieldPath fieldPath;
-    private final Kind kind;
-
-    public Segment(FieldPath fieldPath, Kind kind) {
-      this.fieldPath = fieldPath;
-      this.kind = kind;
-    }
-
     /** The field path of the component. */
-    public FieldPath getFieldPath() {
-      return fieldPath;
-    }
+    public abstract FieldPath getFieldPath();
 
     /** The indexes sorting order. */
-    public Kind getKind() {
-      return kind;
-    }
-
-    @Override
-    public boolean equals(Object o) {
-      if (this == o) return true;
-      if (o == null || getClass() != o.getClass()) return false;
-
-      Segment segment = (Segment) o;
-      if (!fieldPath.equals(segment.fieldPath)) return false;
-      return kind == segment.kind;
-    }
-
-    @Override
-    public int hashCode() {
-      int result = fieldPath.hashCode();
-      result = 31 * result + kind.hashCode();
-      return result;
-    }
+    public abstract Kind getKind();
 
     @Override
     public String toString() {
-      return String.format("Segment{fieldPath=%s, kind=%s}", fieldPath, kind);
+      return String.format("Segment{fieldPath=%s, kind=%s}", getFieldPath(), getKind());
     }
   }
 
@@ -127,7 +100,7 @@ public Iterator<Segment> iterator() {
   /** Returns a new field index with additional index segment. */
   public FieldIndex withAddedField(FieldPath fieldPath, Segment.Kind kind) {
     List<Segment> newSegments = new ArrayList<>(segments);
-    newSegments.add(new Segment(fieldPath, kind));
+    newSegments.add(new AutoValue_FieldIndex_Segment(fieldPath, kind));
     return new FieldIndex(collectionId, newSegments);
   }
 

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

@@ -80,13 +80,13 @@
  * </table>
  */
 public class TargetIndexMatcher {
-  // The collection ID of the query target.
+  // The collection ID (or collection group) of the query target.
   private final String collectionId;
 
   // The list of filters per field. A target can have duplicate filters for a field.
   private final Map<FieldPath, List<FieldFilter>> fieldFilterFields = new HashMap<>();
 
-  // The list of orderBy fields in the query target.
+  // The set of orderBy fields in the query target.
   private final Set<FieldPath> orderByFields = new HashSet<>();
 
   public TargetIndexMatcher(Target target) {