Remove UniqueId.uniqueIdFormat field

documentation/modules/ROOT/partials/release-notes/release-notes-6.1.0-M2.adoc

@@ -25,7 +25,8 @@ repository on GitHub.
 [[v6.1.0-M2-junit-platform-new-features-and-improvements]]
 ==== New Features and Improvements
 
-* ❓
+* The `UniqueId.uniqueIdFormat` field has been removed, reducing the size of `UniqueId`
+  objects.
 
 [[v6.1.0-M2-junit-jupiter]]
 === JUnit Jupiter
@@ -48,6 +49,7 @@ repository on GitHub.
   `DefaultTimeZoneExtension` are now part of the JUnit Jupiter. Find examples in the
   xref:writing-tests/built-in-extensions.adoc#DefaultLocaleAndTimeZone[User Guide].
 
+
 [[v6.1.0-M2-junit-vintage]]
 === JUnit Vintage
 

junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueId.java

@@ -12,6 +12,11 @@
 
 import static org.apiguardian.api.API.Status.STABLE;
 
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.ObjectStreamClass;
+import java.io.ObjectStreamField;
 import java.io.Serial;
 import java.io.Serializable;
 import java.lang.ref.SoftReference;
@@ -40,6 +45,11 @@ public final class UniqueId implements Cloneable, Serializable {
 	@Serial
 	private static final long serialVersionUID = 1L;
 
+	@Serial
+	@SuppressWarnings("UnusedVariable")
+	private static final ObjectStreamField[] serialPersistentFields = ObjectStreamClass.lookup(
+		SerializedForm.class).getFields();
+
 	private static final String ENGINE_SEGMENT_TYPE = "engine";
 
 	/**
@@ -79,33 +89,28 @@ public static UniqueId forEngine(String engineId) {
 	 * @see #forEngine(String)
 	 */
 	public static UniqueId root(String segmentType, String value) {
-		return new UniqueId(UniqueIdFormat.getDefault(), new Segment(segmentType, value));
+		return new UniqueId(new Segment(segmentType, value));
 	}
 
-	private final UniqueIdFormat uniqueIdFormat;
-
-	@SuppressWarnings({ "serial", "RedundantSuppression" }) // always used with serializable implementation (List.copyOf())
-	private final List<Segment> segments;
+	@SuppressWarnings({ "serial", "RedundantSuppression" })
+	// always used with serializable implementation (List.copyOf())
+	// This is effectively final but not technically due to late initialization when deserializing
+	private /* final */ List<Segment> segments;
 
 	// lazily computed
 	private transient int hashCode;
 
 	// lazily computed
 	private transient @Nullable SoftReference<String> toString;
 
-	private UniqueId(UniqueIdFormat uniqueIdFormat, Segment segment) {
-		this(uniqueIdFormat, List.of(segment));
+	private UniqueId(Segment segment) {
+		this(List.of(segment));
 	}
 
 	/**
 	 * Initialize a {@code UniqueId} instance.
-	 *
-	 * @implNote A defensive copy of the segment list is <b>not</b> created by
-	 * this implementation. All callers should immediately drop the reference
-	 * to the list instance that they pass into this constructor.
 	 */
-	UniqueId(UniqueIdFormat uniqueIdFormat, List<Segment> segments) {
-		this.uniqueIdFormat = uniqueIdFormat;
+	UniqueId(List<Segment> segments) {
 		this.segments = List.copyOf(segments);
 	}
 
@@ -164,7 +169,7 @@ public UniqueId append(Segment segment) {
 		List<Segment> baseSegments = new ArrayList<>(this.segments.size() + 1);
 		baseSegments.addAll(this.segments);
 		baseSegments.add(segment);
-		return new UniqueId(this.uniqueIdFormat, baseSegments);
+		return new UniqueId(baseSegments);
 	}
 
 	/**
@@ -215,7 +220,7 @@ public boolean hasPrefix(UniqueId potentialPrefix) {
 	@API(status = STABLE, since = "1.5")
 	public UniqueId removeLastSegment() {
 		Preconditions.condition(this.segments.size() > 1, "Cannot remove last remaining segment");
-		return new UniqueId(uniqueIdFormat, List.copyOf(this.segments.subList(0, this.segments.size() - 1)));
+		return new UniqueId(this.segments.subList(0, this.segments.size() - 1));
 	}
 
 	/**
@@ -234,6 +239,18 @@ protected Object clone() throws CloneNotSupportedException {
 		return super.clone();
 	}
 
+	@Serial
+	private void writeObject(ObjectOutputStream s) throws IOException {
+		SerializedForm serializedForm = new SerializedForm(this);
+		serializedForm.serialize(s);
+	}
+
+	@Serial
+	private void readObject(ObjectInputStream s) throws ClassNotFoundException, IOException {
+		SerializedForm serializedForm = SerializedForm.deserialize(s);
+		segments = serializedForm.segments;
+	}
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) {
@@ -277,7 +294,7 @@ public String toString() {
 		SoftReference<String> s = this.toString;
 		String value = s == null ? null : s.get();
 		if (value == null) {
-			value = this.uniqueIdFormat.format(this);
+			value = UniqueIdFormat.getDefault().format(this);
 			// this is a benign race like String#hash
 			// we potentially read and write values from multiple threads
 			// without a happens-before relationship
@@ -361,4 +378,42 @@ public String toString() {
 
 	}
 
+	/**
+	 * Represents the serialized output of {@code UniqueId}. The fields on this
+	 * class match the fields that {@code UniqueId} had prior to 6.1.
+	 */
+	private static final class SerializedForm implements Serializable {
+
+		@Serial
+		private static final long serialVersionUID = 1L;
+
+		@SuppressWarnings({ "serial", "RedundantSuppression" })
+		// always used with serializable implementation (List.copyOf())
+		private final List<Segment> segments;
+		private final UniqueIdFormat uniqueIdFormat;
+
+		SerializedForm(UniqueId uniqueId) {
+			this.segments = uniqueId.segments;
+			this.uniqueIdFormat = UniqueIdFormat.getDefault();
+		}
+
+		@SuppressWarnings("unchecked")
+		private SerializedForm(ObjectInputStream.GetField fields) throws IOException, ClassNotFoundException {
+			this.segments = (List<Segment>) fields.get("segments", null);
+			this.uniqueIdFormat = UniqueIdFormat.getDefault();
+		}
+
+		void serialize(ObjectOutputStream s) throws IOException {
+			ObjectOutputStream.PutField fields = s.putFields();
+			fields.put("segments", segments);
+			fields.put("uniqueIdFormat", uniqueIdFormat);
+			s.writeFields();
+		}
+
+		static SerializedForm deserialize(ObjectInputStream s) throws IOException, ClassNotFoundException {
+			ObjectInputStream.GetField fields = s.readFields();
+			return new SerializedForm(fields);
+		}
+	}
+
 }

junit-platform-engine/src/main/java/org/junit/platform/engine/UniqueIdFormat.java

@@ -88,7 +88,7 @@ private static String encode(char c) {
 	UniqueId parse(String source) throws JUnitException {
 		String[] parts = source.split(String.valueOf(this.segmentDelimiter));
 		List<Segment> segments = Arrays.stream(parts).map(this::createSegment).toList();
-		return new UniqueId(this, segments);
+		return new UniqueId(segments);
 	}
 
 	private Segment createSegment(String segmentString) throws JUnitException {

platform-tests/src/test/java/org/junit/platform/engine/UniqueIdFormatTests.java

@@ -68,11 +68,21 @@ public String getEngineUid() {
 			return "[engine:junit-jupiter]";
 		}
 
+		@Override
+		public String getDefaultEngineUid() {
+			return getEngineUid();
+		}
+
 		@Override
 		public String getMethodUid() {
 			return "[engine:junit-jupiter]/[class:MyClass]/[method:myMethod]";
 		}
 
+		@Override
+		public String getDefaultMethodUid() {
+			return getMethodUid();
+		}
+
 	}
 
 	@Nested
@@ -90,11 +100,21 @@ public String getEngineUid() {
 			return "{engine=junit-jupiter}";
 		}
 
+		@Override
+		public String getDefaultEngineUid() {
+			return "[engine:junit-jupiter]";
+		}
+
 		@Override
 		public String getMethodUid() {
 			return "{engine=junit-jupiter},{class=MyClass},{method=myMethod}";
 		}
 
+		@Override
+		public String getDefaultMethodUid() {
+			return "[engine:junit-jupiter]/[class:MyClass]/[method:myMethod]";
+		}
+
 	}
 
 	// -------------------------------------------------------------------------
@@ -110,8 +130,12 @@ interface ParsingTestTrait {
 
 		String getEngineUid();
 
+		String getDefaultEngineUid();
+
 		String getMethodUid();
 
+		String getDefaultMethodUid();
+
 		@Test
 		default void parseMalformedUid() {
 			Throwable throwable = assertThrows(JUnitException.class, () -> getFormat().parse("malformed UID"));
@@ -123,7 +147,7 @@ default void parseEngineUid() {
 			var parsedId = getFormat().parse(getEngineUid());
 			assertSegment(parsedId.getSegments().getFirst(), "engine", "junit-jupiter");
 			assertEquals(getEngineUid(), getFormat().format(parsedId));
-			assertEquals(getEngineUid(), parsedId.toString());
+			assertEquals(getDefaultEngineUid(), parsedId.toString());
 		}
 
 		@Test
@@ -133,7 +157,7 @@ default void parseMethodUid() {
 			assertSegment(parsedId.getSegments().get(1), "class", "MyClass");
 			assertSegment(parsedId.getSegments().get(2), "method", "myMethod");
 			assertEquals(getMethodUid(), getFormat().format(parsedId));
-			assertEquals(getMethodUid(), parsedId.toString());
+			assertEquals(getDefaultMethodUid(), parsedId.toString());
 		}
 
 	}

platform-tests/src/test/java/org/junit/platform/engine/UniqueIdTests.java

@@ -18,6 +18,12 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.platform.commons.test.PreconditionAssertions.assertPreconditionViolationFor;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.Base64;
 import java.util.Optional;
 
 import org.junit.jupiter.api.Nested;
@@ -292,6 +298,89 @@ void removesLastSegment() {
 
 	}
 
+	@Nested
+	class Serialization {
+
+		final UniqueId uniqueId = UniqueId.root("engine", "junit-jupiter");
+
+		@Test
+		void roundTrip() throws IOException, ClassNotFoundException {
+			var bytesOut = new ByteArrayOutputStream();
+			var out = new ObjectOutputStream(bytesOut);
+			out.writeObject(uniqueId);
+
+			var bytesIn = new ByteArrayInputStream(bytesOut.toByteArray());
+			var in = new ObjectInputStream(bytesIn);
+			var actual = in.readObject();
+
+			assertEquals(uniqueId, actual);
+			assertEquals(uniqueId.toString(), actual.toString());
+		}
+
+		@Test
+		void deserializeFromJunit60() throws IOException, ClassNotFoundException {
+			/*
+			 Serialized representation of:
+			 	new UniqueId(
+			 		new UniqueIdFormat('[', ':', ']', '/'),
+			 		List.of(new Segment("engine", "junit-jupiter"))
+			 );
+			 */
+			var uniqueIdFromJunit60 = Base64.getMimeDecoder().decode("""
+					rO0ABXNyACJvcmcuanVuaXQucGxhdGZvcm0uZW5naW5lLlVuaXF1ZUlkAAAAAAAAAAECAAJMAAhzZWdtZW50c3QAEExqYXZhL3V0
+					aWwvTGlzdDtMAA51bmlxdWVJZEZvcm1hdHQAKkxvcmcvanVuaXQvcGxhdGZvcm0vZW5naW5lL1VuaXF1ZUlkRm9ybWF0O3hwc3IA
+					EWphdmEudXRpbC5Db2xsU2VyV46rtjobqBEDAAFJAAN0YWd4cAAAAAF3BAAAAAFzcgAqb3JnLmp1bml0LnBsYXRmb3JtLmVuZ2lu
+					ZS5VbmlxdWVJZCRTZWdtZW50AAAAAAAAAAECAAJMAAR0eXBldAASTGphdmEvbGFuZy9TdHJpbmc7TAAFdmFsdWVxAH4AB3hwdAAG
+					ZW5naW5ldAANanVuaXQtanVwaXRlcnhzcgAob3JnLmp1bml0LnBsYXRmb3JtLmVuZ2luZS5VbmlxdWVJZEZvcm1hdAAAAAAAAAAB
+					AgAGQwAMY2xvc2VTZWdtZW50QwALb3BlblNlZ21lbnRDABBzZWdtZW50RGVsaW1pdGVyQwASdHlwZVZhbHVlU2VwYXJhdG9yTAAT
+					ZW5jb2RlZENoYXJhY3Rlck1hcHQAE0xqYXZhL3V0aWwvSGFzaE1hcDtMAA5zZWdtZW50UGF0dGVybnQAGUxqYXZhL3V0aWwvcmVn
+					ZXgvUGF0dGVybjt4cABdAFsALwA6c3IAEWphdmEudXRpbC5IYXNoTWFwBQfawcMWYNEDAAJGAApsb2FkRmFjdG9ySQAJdGhyZXNo
+					b2xkeHA/QAAAAAAADHcIAAAAEAAAAAZzcgATamF2YS5sYW5nLkNoYXJhY3RlcjSLR9lrGiZ4AgABQwAFdmFsdWV4cAAldAADJTI1
+					c3EAfgARADp0AAMlM0FzcQB+ABEAW3QAAyU1QnNxAH4AEQArdAADJTJCc3EAfgARAF10AAMlNURzcQB+ABEAL3QAAyUyRnhzcgAX
+					amF2YS51dGlsLnJlZ2V4LlBhdHRlcm5GZ9VrbkkCDQIAAkkABWZsYWdzTAAHcGF0dGVybnEAfgAHeHAAAAAgdAAXXFFbXEUoLisp
+					XFE6XEUoLispXFFdXEU=""");
+
+			var bytesIn = new ByteArrayInputStream(uniqueIdFromJunit60);
+			var in = new ObjectInputStream(bytesIn);
+			var actual = in.readObject();
+
+			assertEquals(uniqueId, actual);
+			assertEquals(uniqueId.toString(), actual.toString());
+		}
+
+		@Test
+		void deserializeFromJunit60IgnoresCustomFormat() throws IOException, ClassNotFoundException {
+			/*
+			  Serialized representation of:
+				new UniqueId(
+					new UniqueIdFormat('{', '=', '}', ','),
+					List.of(new Segment("engine", "junit-jupiter"))
+			 );
+			 */
+			var uniqueIdWithCustomFormatFromJunit60 = Base64.getMimeDecoder().decode("""
+					rO0ABXNyACJvcmcuanVuaXQucGxhdGZvcm0uZW5naW5lLlVuaXF1ZUlkAAAAAAAAAAECAAJMAAhzZWdtZW50c3QAEExqYXZhL3V0
+					aWwvTGlzdDtMAA51bmlxdWVJZEZvcm1hdHQAKkxvcmcvanVuaXQvcGxhdGZvcm0vZW5naW5lL1VuaXF1ZUlkRm9ybWF0O3hwc3IA
+					EWphdmEudXRpbC5Db2xsU2VyV46rtjobqBEDAAFJAAN0YWd4cAAAAAF3BAAAAAFzcgAqb3JnLmp1bml0LnBsYXRmb3JtLmVuZ2lu
+					ZS5VbmlxdWVJZCRTZWdtZW50AAAAAAAAAAECAAJMAAR0eXBldAASTGphdmEvbGFuZy9TdHJpbmc7TAAFdmFsdWVxAH4AB3hwdAAG
+					ZW5naW5ldAANanVuaXQtanVwaXRlcnhzcgAob3JnLmp1bml0LnBsYXRmb3JtLmVuZ2luZS5VbmlxdWVJZEZvcm1hdAAAAAAAAAAB
+					AgAGQwAMY2xvc2VTZWdtZW50QwALb3BlblNlZ21lbnRDABBzZWdtZW50RGVsaW1pdGVyQwASdHlwZVZhbHVlU2VwYXJhdG9yTAAT
+					ZW5jb2RlZENoYXJhY3Rlck1hcHQAE0xqYXZhL3V0aWwvSGFzaE1hcDtMAA5zZWdtZW50UGF0dGVybnQAGUxqYXZhL3V0aWwvcmVn
+					ZXgvUGF0dGVybjt4cAB9AHsALAA9c3IAEWphdmEudXRpbC5IYXNoTWFwBQfawcMWYNEDAAJGAApsb2FkRmFjdG9ySQAJdGhyZXNo
+					b2xkeHA/QAAAAAAADHcIAAAAEAAAAAZzcgATamF2YS5sYW5nLkNoYXJhY3RlcjSLR9lrGiZ4AgABQwAFdmFsdWV4cAAldAADJTI1
+					c3EAfgARAHt0AAMlN0JzcQB+ABEAK3QAAyUyQnNxAH4AEQAsdAADJTJDc3EAfgARAH10AAMlN0RzcQB+ABEAPXQAAyUzRHhzcgAX
+					amF2YS51dGlsLnJlZ2V4LlBhdHRlcm5GZ9VrbkkCDQIAAkkABWZsYWdzTAAHcGF0dGVybnEAfgAHeHAAAAAgdAAXXFF7XEUoLisp
+					XFE9XEUoLispXFF9XEU=""");
+
+			var bytesIn = new ByteArrayInputStream(uniqueIdWithCustomFormatFromJunit60);
+			var in = new ObjectInputStream(bytesIn);
+			var actual = in.readObject();
+
+			assertEquals(uniqueId, actual);
+			assertEquals(uniqueId.toString(), actual.toString());
+		}
+
+	}
+
 	private static void assertSegment(Segment segment, String expectedType, String expectedValue) {
 		assertEquals(expectedType, segment.getType(), "segment type");
 		assertEquals(expectedValue, segment.getValue(), "segment value");