8312976: MatchResult produces StringIndexOutOfBoundsException for groups outside match

Reviewed-by: alanb, smarks

src/java.base/share/classes/java/util/regex/Matcher.java

@@ -274,13 +274,40 @@ public final class Matcher implements MatchResult {
      * @since 1.5
      */
     public MatchResult toMatchResult() {
-        String capturedText = hasMatch()
-                ? text.subSequence(first, last).toString()
-                : null;
+        int minStart;
+        String capturedText;
+        if (hasMatch()) {
+            minStart = minStart();
+            capturedText = text.subSequence(minStart, maxEnd()).toString();
+        } else {
+            minStart = -1;
+            capturedText = null;
+        }
         return new ImmutableMatchResult(first, last, groupCount(),
                 groups.clone(), capturedText,
-                namedGroups()
-        );
+                namedGroups(), minStart);
+    }
+
+    private int minStart() {
+        int r = text.length();
+        for (int group = 0; group <= groupCount(); ++group) {
+            int start = groups[group * 2];
+            if (start >= 0) {
+                r = Math.min(r, start);
+            }
+        }
+        return r;
+    }
+
+    private int maxEnd() {
+        int r = 0;
+        for (int group = 0; group <= groupCount(); ++group) {
+            int end = groups[group * 2 + 1];
+            if (end >= 0) {
+                r = Math.max(r, end);
+            }
+        }
+        return r;
     }
 
     private static class ImmutableMatchResult implements MatchResult {
@@ -290,16 +317,18 @@ public final class Matcher implements MatchResult {
         private final int[] groups;
         private final String text;
         private final Map<String, Integer> namedGroups;
+        private final int minStart;
 
         ImmutableMatchResult(int first, int last, int groupCount,
                              int[] groups, String text,
-                             Map<String, Integer> namedGroups) {
+                             Map<String, Integer> namedGroups, int minStart) {
             this.first = first;
             this.last = last;
             this.groupCount = groupCount;
             this.groups = groups;
             this.text = text;
             this.namedGroups = namedGroups;
+            this.minStart = minStart;
         }
 
         @Override
@@ -345,7 +374,7 @@ public final class Matcher implements MatchResult {
             checkGroup(group);
             if ((groups[group * 2] == -1) || (groups[group * 2 + 1] == -1))
                 return null;
-            return text.substring(groups[group * 2] - first, groups[group * 2 + 1] - first);
+            return text.substring(groups[group * 2] - minStart, groups[group * 2 + 1] - minStart);
         }
 
         @Override

test/jdk/java/util/regex/ImmutableMatchResultTest.java

@@ -23,8 +23,12 @@
 
 import jdk.test.lib.RandomFactory;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 import java.nio.CharBuffer;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Random;
 import java.util.regex.MatchResult;
@@ -33,10 +37,11 @@ import java.util.regex.Pattern;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
 
 /*
  * @test
- * @bug 8132995
+ * @bug 8132995 8312976
  * @key randomness
  *
  * @summary Tests to exercise the optimization described in the bug report.
@@ -179,4 +184,50 @@ public class ImmutableMatchResultTest {
         testResultsStream(CharBuffer.wrap(inResults));
     }
 
+    static Arguments[] testGroupsOutsideMatch() {
+        return new Arguments[]{
+                arguments("(?<=(\\d{3}))\\D*(?=(\\d{4}))", "-1234abcxyz5678-"),
+                arguments("(?<=(\\d{3}))\\D*(?=(\\1))", "-1234abcxyz2348-"),
+                arguments("(?<!(\\d{4}))\\D+(?=(\\d{4}))", "123abcxyz5678-"),
+        };
+    }
+
+    @ParameterizedTest
+    @MethodSource
+    void testGroupsOutsideMatch(String pattern, String text) {
+        char[] data = text.toCharArray();
+        Matcher m = Pattern.compile(pattern)
+                .matcher(CharBuffer.wrap(data));
+
+        assertEquals(2, m.groupCount());
+        assertTrue(m.find());
+
+        int start = m.start();
+        int end = m.end();
+        String group = m.group();
+
+        int prefixStart = m.start(1);
+        int prefixEnd = m.end(1);
+        String prefixGroup = m.group(1);
+
+        int suffixStart = m.start(2);
+        int suffixEnd = m.end(2);
+        String suffixGroup = m.group(2);
+
+        MatchResult mr = m.toMatchResult();
+        Arrays.fill(data, '*');  // spoil original input
+
+        assertEquals(start, mr.start());
+        assertEquals(end, mr.end());
+        assertEquals(group, mr.group());
+
+        assertEquals(prefixStart, mr.start(1));
+        assertEquals(prefixEnd, mr.end(1));
+        assertEquals(prefixGroup, mr.group(1));
+
+        assertEquals(suffixStart, mr.start(2));
+        assertEquals(suffixEnd, mr.end(2));
+        assertEquals(suffixGroup, mr.group(2));
+    }
+
 }