Use new PolyInitialized qualifier (typetools#39)

Co-authored-by: Werner Dietl <[email protected]>

Author: Ao-senXiong

src/java.base/share/classes/java/lang/Throwable.java

@@ -25,7 +25,7 @@
 
 package java.lang;
 
-import org.checkerframework.checker.initialization.qual.UnknownInitialization;
+import org.checkerframework.checker.initialization.qual.PolyInitialized;
 import org.checkerframework.checker.interning.qual.UsesObjectEquals;
 import org.checkerframework.checker.lock.qual.GuardSatisfied;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -474,7 +474,7 @@ protected Throwable(@Nullable String message, @Nullable Throwable cause,
      *         been called on this throwable.
      * @since  1.4
      */
-    public synchronized @UnknownInitialization Throwable initCause(@UnknownInitialization Throwable this, @Nullable Throwable cause) {
+    public synchronized @PolyInitialized Throwable initCause(@PolyInitialized Throwable this, @Nullable Throwable cause) {
         if (this.cause != this)
             throw new IllegalStateException("Can't overwrite cause with " +
                                             Objects.toString(cause, "a null"), this);

src/java.base/share/classes/org/checkerframework/checker/initialization/qual/PolyInitialized.java

@@ -0,0 +1,27 @@
+package org.checkerframework.checker.initialization.qual;
+
+import org.checkerframework.framework.qual.PolymorphicQualifier;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * A polymorphic qualifier for the freedom-before-commitment initialization tracking type-system.
+ *
+ * <p>Any method written using {@link PolyInitialized} conceptually has multiple versions: one in
+ * which all instances of {@link PolyInitialized} in the method signature have been replaced by one
+ * of the following qualifiers: {@link Initialized}; {@link UnknownInitialization} and {@link
+ * UnderInitialization}, which take a class argument to represent different type frames; and {@link
+ * FBCBottom}.
+ *
+ * @checker_framework.manual #initialization-checker Initialization Checker
+ * @checker_framework.manual #qualifier-polymorphism Qualifier polymorphism
+ */
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
+@PolymorphicQualifier(UnknownInitialization.class)
+public @interface PolyInitialized {}