Add patterns module: pattern matching from JDK 21 to 27

Type, record and primitive patterns, guards, sealed exhaustiveness, MatchException via separate compilation, and eight captured transcripts.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a

patterns/broken/Dominated.java

@@ -0,0 +1,10 @@
+public class Dominated {
+    static String f(Object o) {
+        return switch (o) {
+            case CharSequence cs -> "chars";
+            case String s -> "string";      // String is a CharSequence, so this can never be reached
+            default -> "other";
+        };
+    }
+    public static void main(String[] args) { System.out.println(f("x")); }
+}

patterns/broken/GuardBeforeGeneral.java

@@ -0,0 +1,10 @@
+public class GuardBeforeGeneral {
+    static String f(Object o) {
+        return switch (o) {
+            case String s -> "any string";
+            case String s when s.isEmpty() -> "empty string";   // guarded case after the unguarded one
+            default -> "other";
+        };
+    }
+    public static void main(String[] args) { System.out.println(f("")); }
+}

patterns/broken/NotExhaustive.java

@@ -0,0 +1,15 @@
+public class NotExhaustive {
+    sealed interface Shape permits Circle, Square, Rect {}
+    record Circle(double r) implements Shape {}
+    record Square(double side) implements Shape {}
+    record Rect(double w, double h) implements Shape {}
+
+    static double area(Shape s) {
+        return switch (s) {
+            case Circle(double r) -> Math.PI * r * r;
+            case Square(double side) -> side * side;
+            // Rect is missing
+        };
+    }
+    public static void main(String[] args) { System.out.println(area(new Circle(1))); }
+}

patterns/broken/NotExhaustiveObject.java

@@ -0,0 +1,9 @@
+public class NotExhaustiveObject {
+    static String f(Object o) {
+        return switch (o) {
+            case String s -> "string";
+            case Integer i -> "int";
+        };
+    }
+    public static void main(String[] args) { System.out.println(f("x")); }
+}