[XMLBEANS-676] avoid NamespaceContext thread-local leaks

src/main/java/org/apache/xmlbeans/impl/schema/SchemaLocalAttributeImpl.java

@@ -124,9 +124,9 @@ public XmlAnySimpleType getDefaultValue()
         {
             if (_parseObject != null)
             {
+                NamespaceContext.push(new NamespaceContext(_parseObject));
                 try
                 {
-                    NamespaceContext.push(new NamespaceContext(_parseObject));
                     return getType().newValue(_defaultText);
                 }
                 finally

src/main/java/org/apache/xmlbeans/impl/schema/SchemaParticleImpl.java

@@ -268,8 +268,8 @@ public XmlAnySimpleType getDefaultValue() {
         }
         if (_defaultText != null && XmlAnySimpleType.type.isAssignableFrom(getType())) {
             if (_parseObject != null && XmlQName.type.isAssignableFrom(getType())) {
+                NamespaceContext.push(new NamespaceContext(_parseObject));
                 try {
-                    NamespaceContext.push(new NamespaceContext(_parseObject));
                     return getType().newValue(_defaultText);
                 } finally {
                     NamespaceContext.pop();

src/main/java/org/apache/xmlbeans/impl/values/NamespaceContext.java

@@ -82,8 +82,8 @@ final void push(NamespaceContext next)
         }
         final void pop()
         {
-            current = stack.get(stack.size() - 1);
-            stack.remove(stack.size() - 1);
+            // single remove() so a failure cannot leave current and stack out of step
+            current = stack.remove(stack.size() - 1);
         }
     }
 
@@ -112,16 +112,33 @@ public static void push(NamespaceContext next)
 
     public static void pop()
     {
-        NamespaceContextStack nsContextStack = getNamespaceContextStack();
+        NamespaceContextStack nsContextStack = tl_namespaceContextStack.get();
+        if (nsContextStack == null || nsContextStack.stack.isEmpty())
+        {
+            // unbalanced pop - don't throw (it would mask the original exception), just clean up
+            tl_namespaceContextStack.remove();
+            return;
+        }
+
         nsContextStack.pop();
 
         if (nsContextStack.stack.isEmpty())
-            tl_namespaceContextStack.set(null);
+            tl_namespaceContextStack.remove();
     }
 
     public static PrefixResolver getCurrent()
     {
-        return getNamespaceContextStack().current;
+        // don't create a stack here: nothing would ever remove it from the thread-local
+        NamespaceContextStack nsContextStack = tl_namespaceContextStack.get();
+        return nsContextStack == null ? null : nsContextStack.current;
+    }
+
+    /**
+     * @return true if the current thread has namespace context state (for tests)
+     */
+    static boolean hasThreadLocalState()
+    {
+        return tl_namespaceContextStack.get() != null;
     }
 
     public String getNamespaceForPrefix(String prefix)

src/test/java/org/apache/xmlbeans/impl/values/NamespaceContextTest.java

@@ -0,0 +1,72 @@
+/*   Copyright 2004 The Apache Software Foundation
+ *
+ *   Licensed under the Apache License, Version 2.0 (the "License");
+ *   you may not use this file except in compliance with the License.
+ *   You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *   Unless required by applicable law or agreed to in writing, software
+ *   distributed under the License is distributed on an "AS IS" BASIS,
+ *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *   See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package org.apache.xmlbeans.impl.values;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.Collections;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+// XMLBEANS-676
+public class NamespaceContextTest {
+
+    @AfterEach
+    void cleanUp() {
+        NamespaceContext.clearThreadLocals();
+    }
+
+    @Test
+    void getCurrentDoesNotCreateThreadLocalState() {
+        assertNull(NamespaceContext.getCurrent());
+        assertFalse(NamespaceContext.hasThreadLocalState());
+    }
+
+    @Test
+    void nestedPushPopClearsThreadLocalState() {
+        NamespaceContext outer = new NamespaceContext(Collections.singletonMap("a", "urn:a"));
+        NamespaceContext inner = new NamespaceContext(Collections.singletonMap("b", "urn:b"));
+
+        NamespaceContext.push(outer);
+        NamespaceContext.push(inner);
+        assertSame(inner, NamespaceContext.getCurrent());
+        assertEquals("urn:b", NamespaceContext.getCurrent().getNamespaceForPrefix("b"));
+        NamespaceContext.pop();
+        assertSame(outer, NamespaceContext.getCurrent());
+        assertTrue(NamespaceContext.hasThreadLocalState());
+        NamespaceContext.pop();
+
+        assertNull(NamespaceContext.getCurrent());
+        assertFalse(NamespaceContext.hasThreadLocalState());
+    }
+
+    @Test
+    void unbalancedPopDoesNotThrowOrLeak() {
+        assertDoesNotThrow(NamespaceContext::pop);
+        assertFalse(NamespaceContext.hasThreadLocalState());
+
+        NamespaceContext.push(new NamespaceContext(Collections.emptyMap()));
+        NamespaceContext.pop();
+        assertDoesNotThrow(NamespaceContext::pop);
+        assertFalse(NamespaceContext.hasThreadLocalState());
+    }
+}