Add JSpecify annotations to the API.

build.gradle

@@ -85,6 +85,8 @@ dependencies {
   errorproneJavac 'com.google.errorprone:javac:9+181-r4173-1'
   errorprone 'com.google.errorprone:error_prone_core:2.10.0'
 
+  implementation 'org.jspecify:jspecify:1.0.1'
+
   testCompile 'junit:junit:4.12'
   testCompile 'com.google.gwt:gwt-dev:2.9.0'
   testCompile 'com.google.gwt:gwt-user:2.9.0'

java/com/google/re2j/Matcher.java

@@ -9,6 +9,8 @@
 import com.google.re2j.MatcherInput.Encoding;
 import java.io.UnsupportedEncodingException;
 import java.util.Map;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A stateful iterator that interprets a regex {@code Pattern} on a specific input. Its interface
@@ -38,6 +40,7 @@
  *
  * @author rsc@google.com (Russ Cox)
  */
+@NullMarked
 public final class Matcher {
   // The pattern being matched.
   private final Pattern pattern;
@@ -53,6 +56,7 @@ public final class Matcher {
   // The number of instructions in the pattern.
   private final int numberOfInstructions;
 
+  @SuppressWarnings("nullness:initialization.field.uninitialized")
   private MatcherInput matcherInput;
 
   // The input length in UTF16 codes.
@@ -242,7 +246,7 @@ public String group() {
    * @throws IllegalStateException if there is no match
    * @throws IndexOutOfBoundsException if {@code group < 0} or {@code group > groupCount()}
    */
-  public String group(int group) {
+  public @Nullable String group(int group) {
     int start = start(group);
     int end = end(group);
     if (start < 0 && end < 0) {
@@ -258,7 +262,7 @@ public String group(int group) {
    * @param group the group name
    * @throws IllegalArgumentException if no group with that name exists
    */
-  public String group(String group) {
+  public @Nullable String group(String group) {
     Integer g = namedGroups.get(group);
     if (g == null) {
       throw new IllegalArgumentException("group '" + group + "' not found");

java/com/google/re2j/Pattern.java

@@ -11,6 +11,8 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A compiled representation of an RE2 regular expression, mimicking the
@@ -27,6 +29,7 @@
  *
  * @author rsc@google.com (Russ Cox)
  */
+@NullMarked
 public final class Pattern implements Serializable {
   /** Flag: case insensitive matching. */
   public static final int CASE_INSENSITIVE = 1;
@@ -339,7 +342,7 @@ Object readResolve() {
   }
 
   @Override
-  public boolean equals(Object o) {
+  public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

java/com/google/re2j/PatternSyntaxException.java

@@ -6,11 +6,14 @@
  */
 package com.google.re2j;
 
+import org.jspecify.annotations.NullMarked;
+
 /**
  * An exception thrown by the parser if the pattern was invalid.
  *
  * Following {@code java.util.regex.PatternSyntaxException}, this is an unchecked exception.
  */
+@NullMarked
 public class PatternSyntaxException extends RuntimeException {
 
   private final String error; // the nature of the error