Change DebugExpressionVisitor to output debug information to a generi…

…c Appendable instance

criteria/common/src/org/immutables/criteria/expression/DebugExpressionVisitor.java

@@ -16,26 +16,34 @@
 
 package org.immutables.criteria.expression;
 
+import com.google.common.io.CharStreams;
+
 import java.io.PrintWriter;
 import java.util.Collections;
 import java.util.Objects;
 
 /**
  * Used to output expression tree as string. Useful for debugging expressions.
  */
-public class DebugExpressionVisitor<Void> extends AbstractExpressionVisitor<Void> {
+public class DebugExpressionVisitor<A extends Appendable> extends AbstractExpressionVisitor<A> {
 
   private final PrintWriter writer;
+  private final A target;
 
   private int depth;
 
-  public DebugExpressionVisitor(PrintWriter writer) {
+  public DebugExpressionVisitor(A target) {
     super(e -> { throw new UnsupportedOperationException(); });
-    this.writer = Objects.requireNonNull(writer, "writer");
+    this.target = Objects.requireNonNull(target, "target");
+    this.writer = new PrintWriter(CharStreams.asWriter(target));
+  }
+
+  private A target() {
+    return target;
   }
 
   @Override
-  public Void visit(Call call) {
+  public A visit(Call call) {
     writer.println();
     writer.print(String.join("", Collections.nCopies(depth * 2, " ")));
     writer.print("call op=" + call.operator().name());
@@ -44,21 +52,20 @@ public Void visit(Call call) {
       expr.accept(this);
       depth--;
     }
-    return null;
+    return target();
   }
 
   @Override
-  public Void visit(Constant constant) {
+  public A visit(Constant constant) {
     writer.print(" constant=");
     writer.print(constant.value());
-    return null;
+    return target();
   }
 
   @Override
-  public Void visit(Path path) {
+  public A visit(Path path) {
     writer.print(" path=");
     writer.print(path.toStringPath());
-    return null;
+    return target();
   }
-
 }

criteria/common/src/org/immutables/criteria/expression/Query.java

@@ -113,7 +113,7 @@ public String toString() {
     final StringWriter string = new StringWriter();
     final PrintWriter writer = new PrintWriter(string);
 
-    final DebugExpressionVisitor<Object> visitor = new DebugExpressionVisitor<>(writer);
+    final DebugExpressionVisitor<PrintWriter> visitor = new DebugExpressionVisitor<>(writer);
     writer.append("entity: ").append(entityClass().getName()).println();
 
     if (!projections().isEmpty()) {

criteria/common/src/org/immutables/criteria/expression/SimpleCall.java

@@ -66,7 +66,7 @@ public String toString() {
     printer.append(SimpleCall.class.getSimpleName());
     printer.append("{");
     printer.print(operator().name());
-    DebugExpressionVisitor<Void> debug = new DebugExpressionVisitor<>(printer);
+    DebugExpressionVisitor<PrintWriter> debug = new DebugExpressionVisitor<>(printer);
     arguments().forEach(a -> {
       a.accept(debug);
     });

criteria/common/test/org/immutables/criteria/AggregationExpressionTest.java

@@ -46,10 +46,9 @@ public void aggregation() {
 
   private static void assertProjection(Aggregation<?> aggregation, String ... expectedLines) {
     Expression expression = Matchers.toExpression(aggregation);
-    StringWriter out = new StringWriter();
-    expression.accept(new DebugExpressionVisitor<>(new PrintWriter(out)));
+    String out = expression.accept(new DebugExpressionVisitor<>(new StringBuilder())).toString();
     final String expected = Arrays.stream(expectedLines).collect(Collectors.joining(System.lineSeparator()));
-    Assertions.assertEquals(expected, out.toString().trim());
+    Assertions.assertEquals(expected, out.trim());
   }
 
 

criteria/common/test/org/immutables/criteria/ExpressionAsStringTest.java

@@ -398,9 +398,9 @@ void inner() {
 
 
   private static void assertExpressional(Criterion<?> crit, String ... expectedLines) {
-    final StringWriter out = new StringWriter();
+    final StringBuilder out = new StringBuilder();
     Query query = Criterias.toQuery(crit);
-    query.filter().ifPresent(f -> f.accept(new DebugExpressionVisitor<>(new PrintWriter(out))));
+    query.filter().ifPresent(f -> f.accept(new DebugExpressionVisitor<>(out)));
     final String expected = Arrays.stream(expectedLines).collect(Collectors.joining(System.lineSeparator()));
     Assertions.assertEquals(expected, out.toString().trim());
   }