add ConfigValue.render() which returns a String version of the value

also toString() includes the render() plus the class name.

src/main/java/com/typesafe/config/ConfigValue.java

@@ -43,6 +43,18 @@ public interface ConfigValue extends ConfigMergeable {
      */
     Object unwrapped();
 
+    /**
+     * Renders the config value as a HOCON string. This method is primarily
+     * intended for debugging, so it tries to add helpful comments and
+     * whitespace. If the config value has not been resolved (see
+     * {@link Config#resolve}), it's possible that it can't be rendered as valid
+     * HOCON. In that case the rendering should still be useful for debugging
+     * but you might not be able to parse it.
+     * 
+     * @return the rendered value
+     */
+    String render();
+
     @Override
     ConfigValue withFallback(ConfigMergeable other);
 }

src/main/java/com/typesafe/config/impl/AbstractConfigObject.java

@@ -261,20 +261,24 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements
     }
 
     @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append(valueType().name());
-        sb.append("(");
-        for (String k : keySet()) {
-            sb.append(k);
-            sb.append("->");
-            sb.append(peek(k).toString());
-            sb.append(",");
+    protected void render(StringBuilder sb, int indent) {
+        if (isEmpty()) {
+            sb.append("{}");
+        } else {
+            sb.append("{\n");
+            for (String k : keySet()) {
+                AbstractConfigValue v = peek(k);
+                indent(sb, indent + 1);
+                sb.append("# ");
+                sb.append(v.origin().description());
+                sb.append("\n");
+                indent(sb, indent + 1);
+                v.render(sb, indent + 1, k);
+                sb.append(",\n");
+            }
+            indent(sb, indent);
+            sb.append("}");
         }
-        if (!keySet().isEmpty())
-            sb.setLength(sb.length() - 1); // chop comma
-        sb.append(")");
-        return sb.toString();
     }
 
     private static boolean mapEquals(Map<String, ConfigValue> a,

src/main/java/com/typesafe/config/impl/AbstractConfigValue.java

@@ -162,8 +162,37 @@ abstract class AbstractConfigValue implements ConfigValue {
     }
 
     @Override
-    public String toString() {
-        return valueType().name() + "(" + unwrapped() + ")";
+    public final String toString() {
+        return getClass().getSimpleName() + "(" + render() + ")";
+    }
+
+    protected static void indent(StringBuilder sb, int indent) {
+        int remaining = indent;
+        while (remaining > 0) {
+            sb.append("    ");
+            --remaining;
+        }
+    }
+
+    protected void render(StringBuilder sb, int indent, String atKey) {
+        if (atKey != null) {
+            sb.append(ConfigUtil.renderJsonString(atKey));
+            sb.append(" : ");
+        }
+        render(sb, indent);
+    }
+
+    protected void render(StringBuilder sb, int indent) {
+        Object u = unwrapped();
+        sb.append(u.toString());
+    }
+
+
+    @Override
+    public final String render() {
+        StringBuilder sb = new StringBuilder();
+        render(sb, 0, null);
+        return sb.toString();
     }
 
     // toString() is a debugging-oriented string but this is defined

src/main/java/com/typesafe/config/impl/ConfigDelayedMerge.java

@@ -5,6 +5,7 @@ package com.typesafe.config.impl;
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 
 import com.typesafe.config.ConfigException;
@@ -160,16 +161,46 @@ final class ConfigDelayedMerge extends AbstractConfigValue implements
     }
 
     @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append("DELAYED_MERGE");
-        sb.append("(");
-        for (Object s : stack) {
-            sb.append(s.toString());
-            sb.append(",");
+    protected void render(StringBuilder sb, int indent, String atKey) {
+        render(stack, sb, indent, atKey);
+    }
+
+    // static method also used by ConfigDelayedMergeObject.
+    static void render(List<AbstractConfigValue> stack, StringBuilder sb, int indent, String atKey) {
+        sb.append("# unresolved merge of " + stack.size() + " values follows (\n");
+        if (atKey == null) {
+            indent(sb, indent);
+            sb.append("# this unresolved merge will not be parseable because it's at the root of the object\n");
+            sb.append("# the HOCON format has no way to list multiple root objects in a single file\n");
         }
-        sb.setLength(sb.length() - 1); // chop comma
-        sb.append(")");
-        return sb.toString();
+
+        List<AbstractConfigValue> reversed = new ArrayList<AbstractConfigValue>();
+        reversed.addAll(stack);
+        Collections.reverse(reversed);
+
+        int i = 0;
+        for (AbstractConfigValue v : reversed) {
+            indent(sb, indent);
+            if (atKey != null) {
+                sb.append("#     unmerged value " + i + " for key "
+                        + ConfigUtil.renderJsonString(atKey) + " from ");
+            } else {
+                sb.append("#     unmerged value " + i + " from ");
+            }
+            i += 1;
+            sb.append(v.origin().description());
+            sb.append("\n");
+            indent(sb, indent);
+            if (atKey != null) {
+                sb.append(ConfigUtil.renderJsonString(atKey));
+                sb.append(" : ");
+            }
+            v.render(sb, indent);
+            sb.append(",\n");
+        }
+        sb.setLength(sb.length() - 2); // chop comma and newline
+        sb.append("\n");
+        indent(sb, indent);
+        sb.append("# ) end of unresolved merge\n");
     }
 }

src/main/java/com/typesafe/config/impl/ConfigDelayedMergeObject.java

@@ -139,17 +139,8 @@ class ConfigDelayedMergeObject extends AbstractConfigObject implements
     }
 
     @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append("DELAYED_MERGE_OBJECT");
-        sb.append("(");
-        for (Object s : stack) {
-            sb.append(s.toString());
-            sb.append(",");
-        }
-        sb.setLength(sb.length() - 1); // chop comma
-        sb.append(")");
-        return sb.toString();
+    protected void render(StringBuilder sb, int indent, String atKey) {
+        ConfigDelayedMerge.render(stack, sb, indent, atKey);
     }
 
     private static ConfigException notResolved() {

src/main/java/com/typesafe/config/impl/ConfigNull.java

@@ -34,4 +34,9 @@ final class ConfigNull extends AbstractConfigValue {
     String transformToString() {
         return "null";
     }
+
+    @Override
+    protected void render(StringBuilder sb, int indent) {
+        sb.append("null");
+    }
 }

src/main/java/com/typesafe/config/impl/ConfigString.java

@@ -29,4 +29,9 @@ final class ConfigString extends AbstractConfigValue {
     String transformToString() {
         return value;
     }
+
+    @Override
+    protected void render(StringBuilder sb, int indent) {
+        sb.append(ConfigUtil.renderJsonString(value));
+    }
 }

src/main/java/com/typesafe/config/impl/ConfigSubstitution.java

@@ -244,16 +244,15 @@ final class ConfigSubstitution extends AbstractConfigValue implements
     }
 
     @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append("SUBST");
-        sb.append("(");
+    protected void render(StringBuilder sb, int indent) {
         for (Object p : pieces) {
-            sb.append(p.toString());
-            sb.append(",");
+            if (p instanceof Path) {
+                sb.append("${");
+                sb.append(((Path) p).render());
+                sb.append("}");
+            } else {
+                sb.append(ConfigUtil.renderJsonString((String) p));
+            }
         }
-        sb.setLength(sb.length() - 1); // chop comma
-        sb.append(")");
-        return sb.toString();
     }
 }

src/main/java/com/typesafe/config/impl/SimpleConfigList.java

@@ -135,18 +135,26 @@ final class SimpleConfigList extends AbstractConfigValue implements ConfigList {
     }
 
     @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        sb.append(valueType().name());
-        sb.append("(");
-        for (ConfigValue e : value) {
-            sb.append(e.toString());
-            sb.append(",");
+    protected void render(StringBuilder sb, int indent) {
+        if (value.isEmpty()) {
+            sb.append("[]");
+        } else {
+            sb.append("[\n");
+            for (AbstractConfigValue v : value) {
+                indent(sb, indent + 1);
+                sb.append("# ");
+                sb.append(v.origin().description());
+                sb.append("\n");
+                indent(sb, indent + 1);
+                v.render(sb, indent + 1);
+                sb.append(",\n");
+            }
+            sb.setLength(sb.length() - 2); // chop comma and newline
+            sb.append("\n");
+
+            indent(sb, indent);
+            sb.append("]");
         }
-        if (!value.isEmpty())
-            sb.setLength(sb.length() - 1); // chop comma
-        sb.append(")");
-        return sb.toString();
     }
 
     @Override

src/test/resources/test06.conf

@@ -0,0 +1,14 @@
+## This file tests ConfigDelayedMerge and ConfigDelayedMergeObject
+
+a=1
+b=2
+c=3
+d={ "foo" : "bar" }
+
+# merge some x's
+x=${a}
+x=${b}
+
+# merge some y's where we know one is an object
+y=${d}
+y={ "hello" : "world", "foo" : 10 }

src/test/scala/Rendering.scala

@@ -0,0 +1,18 @@
+import com.typesafe.config.ConfigFactory
+
+object RenderExample extends App {
+    def render(what: String) {
+        val conf = ConfigFactory.loadWithoutResolving(what)
+
+        println("=== BEGIN UNRESOLVED " + what)
+        println(conf.root.render())
+        println("=== END UNRESOLVED " + what)
+
+        println("=== BEGIN RESOLVED " + what)
+        println(conf.resolve().root.render())
+        println("=== END RESOLVED " + what)
+    }
+
+    render("test01")
+    render("test06")
+}

src/test/scala/com/typesafe/config/impl/ConfParserTest.scala

@@ -57,6 +57,12 @@ class ConfParserTest extends TestUtils {
             val ourAST = addOffendingJsonToException("config-conf", valid.test) {
                 parse(valid.test)
             }
+            // let's also check round-trip rendering
+            val rendered = ourAST.render()
+            val reparsed = addOffendingJsonToException("config-conf-reparsed", rendered) {
+                parse(rendered)
+            }
+            assertEquals(ourAST, reparsed)
         }
     }
 

src/test/scala/com/typesafe/config/impl/ConfigTest.scala

@@ -866,4 +866,33 @@ class ConfigTest extends TestUtils {
         assertEquals("prod", conf.getString("%prod.application.mode"))
         assertEquals("Yet another blog", conf.getString("blog.title"))
     }
+
+    @Test
+    def test06Merge() {
+        // test06 mostly exists because its render() round trip is tricky
+        val conf = ConfigFactory.load("test06")
+
+        assertEquals(2, conf.getInt("x"))
+        assertEquals(10, conf.getInt("y.foo"))
+        assertEquals("world", conf.getString("y.hello"))
+    }
+
+    @Test
+    def renderRoundTrip() {
+        for (i <- 1 to 6) {
+            val conf = ConfigFactory.loadWithoutResolving("test0" + i)
+            val unresolvedRender = conf.root.render()
+            val resolved = conf.resolve()
+            val resolvedRender = resolved.root.render()
+            try {
+                assertEquals(conf.root, ConfigFactory.parseString(unresolvedRender, ConfigParseOptions.defaults()).root)
+                assertEquals(resolved.root, ConfigFactory.parseString(resolvedRender, ConfigParseOptions.defaults()).root)
+            } catch {
+                case e: Throwable =>
+                    System.err.println("unresolvedRender = " + unresolvedRender)
+                    System.err.println("resolvedRender = " + resolvedRender)
+                    throw e
+            }
+        }
+    }
 }