Fix JVM_GetSystemPackage(s)

* Avoid NPE when the package entry is not found
* Don't list package for which no class was loaded. This must be
  directly tied to which packages were seen in
  `BootClassRegistry.loadKlassImpl` and thus have a "boot classpath
  location".

Author: gilles-duboscq

espresso/src/com.oracle.truffle.espresso.classfile/src/com/oracle/truffle/espresso/classfile/tables/EntryTable.java

@@ -26,8 +26,10 @@
 import java.util.Objects;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReadWriteLock;
+import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.espresso.classfile.descriptors.Name;
 import com.oracle.truffle.espresso.classfile.descriptors.Symbol;
 
@@ -49,10 +51,11 @@ public void collectValues(Consumer<T> consumer) {
         }
     }
 
-    @SuppressWarnings({"try", "unchecked", "rawtypes"})
-    public Symbol<Name>[] getKeys() {
+    @SuppressWarnings("try")
+    @TruffleBoundary
+    public void collectEntries(BiConsumer<Symbol<Name>, T> consumer) {
         try (BlockLock block = read()) {
-            return entries.keySet().toArray(new Symbol[entries.size()]);
+            entries.forEach(consumer::accept);
         }
     }
 

espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/impl/BootClassRegistry.java

@@ -23,9 +23,7 @@
 
 package com.oracle.truffle.espresso.impl;
 
-import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.espresso.classfile.ClasspathFile;
-import com.oracle.truffle.espresso.classfile.descriptors.Name;
 import com.oracle.truffle.espresso.classfile.descriptors.Symbol;
 import com.oracle.truffle.espresso.classfile.descriptors.Type;
 import com.oracle.truffle.espresso.classfile.descriptors.TypeSymbols;
@@ -82,11 +80,6 @@ public Klass loadKlassImpl(EspressoContext context, Symbol<Type> type) throws Es
         return result;
     }
 
-    @TruffleBoundary
-    public Symbol<Name>[] getPackages() {
-        return packages().getKeys();
-    }
-
     @Override
     public @JavaType(ClassLoader.class) StaticObject getClassLoader() {
         return StaticObject.NULL;

espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/vm/VM.java

@@ -550,6 +550,9 @@ public static void JVM_GC() {
         }
         BootClassRegistry bootClassRegistry = getRegistries().getBootClassRegistry();
         PackageEntry packageEntry = bootClassRegistry.packages().lookup(pkgName);
+        if (packageEntry == null) {
+            return StaticObject.NULL;
+        }
         ModuleEntry moduleEntry = packageEntry.module();
         if (moduleEntry != null) {
             String location = moduleEntry.location();
@@ -562,12 +565,13 @@ public static void JVM_GC() {
 
     @VmImpl(isJni = true)
     public @JavaType(String[].class) StaticObject JVM_GetSystemPackages(@Inject Meta meta) {
-        Symbol<Name>[] packageSymbols = getRegistries().getBootClassRegistry().getPackages();
-        StaticObject[] array = new StaticObject[packageSymbols.length];
-        for (int i = 0; i < packageSymbols.length; i++) {
-            array[i] = meta.toGuestString(packageSymbols[i]);
-        }
-        return StaticObject.createArray(meta.java_lang_String.getArrayClass(), array, getContext());
+        List<StaticObject> packageNames = new ArrayList<>();
+        getRegistries().getBootClassRegistry().packages().collectEntries((s, p) -> {
+            if (p.getBootClasspathLocation() != null) {
+                packageNames.add(meta.toGuestString(s));
+            }
+        });
+        return StaticObject.createArray(meta.java_lang_String.getArrayClass(), packageNames.toArray(new StaticObject[packageNames.size()]), getContext());
     }
 
     @VmImpl