Fix circular reference support in toString of collection classes (#552)

classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java

@@ -56,6 +56,10 @@ class TAbstractStringBuilder extends TObject implements TSerializable, TCharSequ
         length = value.length();
     }
 
+    public TAbstractStringBuilder append(Object obj) {
+        return append(String.valueOf(obj));
+    }
+
     protected TAbstractStringBuilder append(String string) {
         return insert(length, string);
     }

classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuffer.java

@@ -32,6 +32,11 @@ public class TStringBuffer extends TAbstractStringBuilder implements TAppendable
         super(value);
     }
 
+    @Override
+    public TStringBuffer append(Object obj) {
+        return append(String.valueOf(obj));
+    }
+
     @Override
     public TStringBuffer append(String string) {
         super.append(string);

classlib/src/main/java/org/teavm/classlib/java/lang/TStringBuilder.java

@@ -32,6 +32,11 @@ public class TStringBuilder extends TAbstractStringBuilder implements TAppendabl
         super(value);
     }
 
+    @Override
+    public TStringBuilder append(Object obj) {
+        return append(String.valueOf(obj));
+    }
+
     @Override
     public TStringBuilder append(String string) {
         super.append(string);

classlib/src/main/java/org/teavm/classlib/java/util/TAbstractCollection.java

@@ -142,15 +142,17 @@ public abstract class TAbstractCollection<E> extends TObject implements TCollect
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
-        sb.append("[");
+        sb.append('[');
         TIterator<E> iter = iterator();
         if (iter.hasNext()) {
-            sb.append(String.valueOf(iter.next()));
+            E e = iter.next();
+            sb.append(e == this ? "(this Collection)" : iter.next());
         }
         while (iter.hasNext()) {
-            sb.append(", ").append(String.valueOf(iter.next()));
+            E e = iter.next();
+            sb.append(", ").append(e == this ? "(this Collection)" : iter.next());
         }
-        sb.append("]");
+        sb.append(']');
         return sb.toString();
     }
 }

classlib/src/main/java/org/teavm/classlib/java/util/TAbstractMap.java

@@ -265,6 +265,28 @@ public abstract class TAbstractMap<K, V> extends TObject implements TMap<K, V> {
         return result;
     }
 
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        sb.append('{');
+        TIterator<TMap.Entry<K, V>> iter = entrySet().iterator();
+        if (iter.hasNext()) {
+            TMap.Entry<K, V> e = iter.next();
+            sb.append(e.getKey() == this ? "(this Map)" : e.getKey());
+            sb.append('=');
+            sb.append(e.getValue() == this ? "(this Map)" : e.getValue());
+        }
+        while (iter.hasNext()) {
+            sb.append(", ");
+            TMap.Entry<K, V> e = iter.next();
+            sb.append(e.getKey() == this ? "(this Map)" : e.getKey());
+            sb.append('=');
+            sb.append(e.getValue() == this ? "(this Map)" : e.getValue());
+        }
+        sb.append('}');
+        return sb.toString();
+    }
+
     @Override
     protected Object clone() throws TCloneNotSupportedException {
         TAbstractMap<?, ?> copy = (TAbstractMap<?, ?>) super.clone();

classlib/src/main/java/org/teavm/classlib/java/util/TArrayList.java

@@ -195,4 +195,19 @@ public class TArrayList<E> extends TAbstractList<E> implements TCloneable, TSeri
             action.accept(array[i]);
         }
     }
+
+    @Override
+    public String toString() {
+        if (size == 0) {
+            return "[]";
+        }
+        int length = size - 1;
+        StringBuilder buffer = new StringBuilder(size * 16);
+        buffer.append('[');
+        for (int i = 0; i < length; i++) {
+            buffer.append(array[i] == this ? "(this Collection)" : array[i]).append(", ");
+        }
+        buffer.append(array[length] == this ? "(this Collection)" : array[length]);
+        return buffer.append(']').toString();
+    }
 }

tests/src/test/java/org/teavm/classlib/java/util/ArrayListTest.java

@@ -174,4 +174,14 @@ public class ArrayListTest {
         assertEquals("A1", list.get(0));
         assertEquals("B1", list.get(1));
     }
+
+    @Test
+    public void testToString() {
+        List list = new ArrayList<>();
+        list.add(list);
+        list.add("A");
+
+        assertEquals("[(this Collection), A]", list.toString());
+        assertEquals("[]", new ArrayList().toString());
+    }
 }

tests/src/test/java/org/teavm/classlib/java/util/LinkedHashMapTest.java

@@ -550,4 +550,14 @@ public class LinkedHashMapTest {
         }
         assertTrue("Entries left to iterate on", !it2.hasNext());
     }
+
+    @Test
+    public void test_to_String() {
+        LinkedHashMap lhm = new LinkedHashMap();
+        lhm.put("A", lhm);
+        lhm.put("B", "C");
+
+        assertEquals("{A=(this Map), B=C}", lhm.toString());
+        assertEquals("{}", new LinkedHashMap().toString());
+    }
 }