Apply suggestions from code review.

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/DynamicContext.java

@@ -34,6 +34,7 @@
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
 
 import edu.umd.cs.findbugs.annotations.NonNull;
 import edu.umd.cs.findbugs.annotations.Nullable;
@@ -326,7 +327,9 @@ public void pushExecutionStack(@NonNull IExpression expression) {
    */
   public void popExecutionStack(@NonNull IExpression expression) {
     IExpression popped = this.sharedState.executionStack.pop();
-    assert expression.equals(popped);
+    if (!expression.equals(popped)) {
+        throw new IllegalStateException("Popped expression does not match expected expression");
+    }
   }
 
   /**
@@ -339,6 +342,18 @@ public List<IExpression> getExecutionStack() {
     return CollectionUtil.unmodifiableList(new ArrayList<>(this.sharedState.executionStack));
   }
 
+  /**
+   * Provides a formatted stack trace.
+   *
+   * @return the formatted stack trace
+   */
+  @NonNull
+  public String formatExecutionStackTrace() {
+    return ObjectUtils.notNull(getExecutionStack().stream()
+        .map(IExpression::toCSTString)
+        .collect(Collectors.joining("\n-> ")));
+  }
+
   private class CachingLoader implements IDocumentLoader {
     @NonNull
     private final IDocumentLoader proxy;

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/items/AbstractLiteralExpression.java

@@ -13,8 +13,7 @@
 import edu.umd.cs.findbugs.annotations.NonNull;
 
 /**
- * A base class for all Metapath
- * <a href="https://www.w3.org/TR/xpath-31/#id-literals">literal value
+ * A base class for all Metapath <a href="https://www.w3.org/TR/xpath-31/#id-literals">literal value
  * expressions</a>.
  *
  * @param <RESULT_TYPE>
@@ -45,7 +44,7 @@ public RESULT_TYPE getValue() {
   }
 
   @Override
-  protected ISequence<?> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
+  protected ISequence<RESULT_TYPE> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
     return ISequence.of(getValue());
   }
 

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/items/Except.java

@@ -11,21 +11,22 @@
 import gov.nist.secauto.metaschema.core.metapath.item.ISequence;
 import gov.nist.secauto.metaschema.core.util.ObjectUtils;
 
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import edu.umd.cs.findbugs.annotations.NonNull;
 
 /**
- * The CST node for a Metapath
- * <a href="https://www.w3.org/TR/xpath-31/#combining_seq">except
+ * The CST node for a Metapath <a href="https://www.w3.org/TR/xpath-31/#combining_seq">except
  * expression</a>.
  */
 public class Except
     extends AbstractFilterExpression {
 
   /**
-   * Construct a except filter expression, which removes the items resulting from
-   * the filter expression from the items expression.
+   * Construct a except filter expression, which removes the items resulting from the filter
+   * expression from the items expression.
    *
    * @param text
    *          the parsed text of the expression
@@ -43,8 +44,9 @@ public Except(
 
   @Override
   protected ISequence<?> applyFilterTo(@NonNull List<? extends IItem> source, @NonNull List<? extends IItem> items) {
+    Set<IItem> filterSet = new HashSet<>(items);
     return ISequence.of(ObjectUtils.notNull(source.stream()
-        .filter(item -> !items.contains(item))));
+        .filter(item -> !filterSet.contains(item))));
   }
 
   @Override

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/items/Intersect.java

@@ -16,15 +16,14 @@
 import edu.umd.cs.findbugs.annotations.NonNull;
 
 /**
- * The CST node for a Metapath
- * <a href="https://www.w3.org/TR/xpath-31/#combining_seq">intersect
+ * The CST node for a Metapath <a href="https://www.w3.org/TR/xpath-31/#combining_seq">intersect
  * expression</a>.
  */
 public class Intersect
     extends AbstractFilterExpression {
 
   /**
-   * Construct a new Metapath except expression CST node.
+   * Construct a new Metapath intersect expression CST node.
    *
    * @param text
    *          the parsed text of the expression

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/items/Quantified.java

@@ -30,8 +30,7 @@
 import edu.umd.cs.findbugs.annotations.NonNull;
 
 /**
- * An XPath 3.1 <a href=
- * "https://www.w3.org/TR/xpath-31/#id-quantified-expressions">quantified
+ * An XPath 3.1 <a href= "https://www.w3.org/TR/xpath-31/#id-quantified-expressions">quantified
  * expression</a>.
  */
 public class Quantified
@@ -41,23 +40,21 @@ public class Quantified
    */
   public enum Quantifier {
     /**
-     * The quantified expression is {@code true} if at least one evaluation of the
-     * test expression has the
-     * <a href="https://www.w3.org/TR/xpath-31/#dt-ebv">effective boolean value</a>
-     * {@code true}; otherwise the quantified expression is {@code false}.
+     * The quantified expression is {@code true} if at least one evaluation of the test expression has
+     * the <a href="https://www.w3.org/TR/xpath-31/#dt-ebv">effective boolean value</a> {@code true};
+     * otherwise the quantified expression is {@code false}.
      * <p>
-     * This rule implies that, if the in-clauses generate zero binding tuples, the
-     * value of the quantified expression is {@code false}.
+     * This rule implies that, if the in-clauses generate zero binding tuples, the value of the
+     * quantified expression is {@code false}.
      */
     SOME,
     /**
-     * the quantified expression is {@code true} if every evaluation of the test
-     * expression has the <a href="https://www.w3.org/TR/xpath-31/#dt-ebv">effective
-     * boolean value</a> {@code true}; otherwise the quantified expression is
-     * {@code false}.
+     * the quantified expression is {@code true} if every evaluation of the test expression has the
+     * <a href="https://www.w3.org/TR/xpath-31/#dt-ebv">effective boolean value</a> {@code true};
+     * otherwise the quantified expression is {@code false}.
      * <p>
-     * This rule implies that, if the in-clauses generate zero binding tuples, the
-     * value of the quantified expression is {@code true}.
+     * This rule implies that, if the in-clauses generate zero binding tuples, the value of the
+     * quantified expression is {@code true}.
      */
     EVERY;
   }
@@ -77,11 +74,10 @@ public enum Quantifier {
    * @param quantifier
    *          the quantifier operation
    * @param inClauses
-   *          the set of expressions that define the variables to use for
-   *          determining the Cartesian product for evaluation
+   *          the set of expressions that define the variables to use for determining the Cartesian
+   *          product for evaluation
    * @param satisfies
-   *          the expression used for evaluation using the Cartesian product of
-   *          the variables
+   *          the expression used for evaluation using the Cartesian product of the variables
    */
   public Quantified(
       @NonNull String text,
@@ -105,8 +101,8 @@ public Quantifier getQuantifier() {
   }
 
   /**
-   * Get the set of expressions that define the variables to use for determining
-   * the Cartesian product for evaluation.
+   * Get the set of expressions that define the variables to use for determining the Cartesian product
+   * for evaluation.
    *
    * @return the variable names mapped to the associated Metapath expression
    */
@@ -116,8 +112,7 @@ public Map<IEnhancedQName, IExpression> getInClauses() {
   }
 
   /**
-   * Get the expression used for evaluation using the Cartesian product of the
-   * variables.
+   * Get the expression used for evaluation using the Cartesian product of the variables.
    *
    * @return the evaluation expression
    */
@@ -133,7 +128,7 @@ public List<? extends IExpression> getChildren() {
   }
 
   @Override
-  protected ISequence<?> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
+  protected ISequence<IBooleanItem> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
     Map<IEnhancedQName, ISequence<? extends IItem>> clauses = getInClauses().entrySet().stream()
         .map(entry -> Map.entry(
             entry.getKey(),

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/path/RootSlashOnlyPath.java

@@ -23,13 +23,11 @@
 /**
  * An expression that gets the document root.
  * <p>
- * Based on the XPath 3.1
- * <a href= "https://www.w3.org/TR/xpath-31/#id-path-operator">path
+ * Based on the XPath 3.1 <a href= "https://www.w3.org/TR/xpath-31/#id-path-operator">path
  * operator</a>.
  * <p>
- * This class handles the root path expression "/", which selects the document
- * root node when evaluated. The evaluation follows the XPath specification for
- * absolute paths.
+ * This class handles the root path expression "/", which selects the document root node when
+ * evaluated. The evaluation follows the XPath specification for absolute paths.
  */
 public class RootSlashOnlyPath
     extends AbstractPathExpression<INodeItem> {
@@ -63,15 +61,21 @@ public <RESULT, CONTEXT> RESULT accept(IExpressionVisitor<RESULT, CONTEXT> visit
   protected ISequence<? extends INodeItem> evaluate(DynamicContext dynamicContext, ISequence<?> focus) {
     return ISequence.of(ObjectUtils.notNull(focus.stream()
         .map(ItemUtils::checkItemIsNodeItemForStep)
-        .map(item -> Axis.ANCESTOR_OR_SELF.execute(ObjectUtils.notNull(item))
-            .findFirst()
-            .orElseThrow(() -> new DynamicMetapathException(DynamicMetapathException.TREAT_DOES_NOT_MATCH_TYPE,
-                "Root node not found")))
-        .peek(item -> {
-          if (!(item instanceof IDocumentNodeItem)) {
-            throw new DynamicMetapathException(DynamicMetapathException.TREAT_DOES_NOT_MATCH_TYPE,
-                "The head of the tree is not a document node.");
-          }
-        })));
+        .map(RootSlashOnlyPath::findAndValidateDocumentRoot)));
+  }
+
+  private static INodeItem findAndValidateDocumentRoot(INodeItem item) {
+    INodeItem root = Axis.ANCESTOR_OR_SELF.execute(ObjectUtils.notNull(item))
+        .findFirst()
+        .orElseThrow(() -> new DynamicMetapathException(
+            DynamicMetapathException.TREAT_DOES_NOT_MATCH_TYPE,
+            "Root node not found"));
+
+    if (!(root instanceof IDocumentNodeItem)) {
+      throw new DynamicMetapathException(
+          DynamicMetapathException.TREAT_DOES_NOT_MATCH_TYPE,
+          "The head of the tree is not a document node.");
+    }
+    return root;
   }
 }

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/type/InstanceOf.java

@@ -24,8 +24,7 @@
  */
 /**
  * A compact syntax tree node that supports the Metapath
- * <a href="https://www.w3.org/TR/xpath-31/#id-instance-of">"instance of"
- * operator</a>.
+ * <a href="https://www.w3.org/TR/xpath-31/#id-instance-of">"instance of" operator</a>.
  */
 public class InstanceOf
     extends AbstractExpression {