add atPath() and atKey() to place a value inside a Config

Otherwise it's sort of clunky to do this because you have to
create a map then parseMap, or other roundabout approach.

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

@@ -506,4 +506,25 @@ public interface Config extends ConfigMergeable {
      * @return a copy of the config minus the specified path
      */
     Config withoutPath(String path);
+
+    /**
+     * Places the config inside another {@code Config} at the given path.
+     *
+     * @param path
+     *            path to store this config at.
+     * @return a {@code Config} instance containing this config at the given
+     *         path.
+     */
+    Config atPath(String path);
+
+    /**
+     * Places the config inside a {@code Config} at the given key. See also
+     * atPath().
+     *
+     * @param key
+     *            key to store this config at.
+     * @return a {@code Config} instance containing this config at the given
+     *         key.
+     */
+    Config atKey(String key);
 }

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

@@ -76,7 +76,7 @@ public interface ConfigValue extends ConfigMergeable {
      * HOCON-specific features (such as comments), the rendering will be valid
      * JSON. If you enable HOCON-only features such as comments, the rendering
      * will not be valid JSON.
-     * 
+     *
      * @param options
      *            the rendering options
      * @return the rendered value
@@ -85,4 +85,25 @@ public interface ConfigValue extends ConfigMergeable {
 
     @Override
     ConfigValue withFallback(ConfigMergeable other);
+
+    /**
+     * Places the value inside a {@code Config} at the given path. See also
+     * atKey().
+     *
+     * @param path
+     *            path to store this value at.
+     * @return a {@code Config} instance containing this value at the given
+     *         path.
+     */
+    Config atPath(String path);
+
+    /**
+     * Places the value inside a {@code Config} at the given key. See also
+     * atPath().
+     *
+     * @param key
+     *            key to store this value at.
+     * @return a {@code Config} instance containing this value at the given key.
+     */
+    Config atKey(String key);
 }

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

@@ -7,7 +7,9 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
+import com.typesafe.config.Config;
 import com.typesafe.config.ConfigException;
 import com.typesafe.config.ConfigMergeable;
 import com.typesafe.config.ConfigOrigin;
@@ -327,4 +329,28 @@ abstract class AbstractConfigValue implements ConfigValue, MergeableValue {
     String transformToString() {
         return null;
     }
+
+    SimpleConfig atKey(ConfigOrigin origin, String key) {
+        Map<String, AbstractConfigValue> m = Collections.singletonMap(key, this);
+        return (new SimpleConfigObject(origin, m)).toConfig();
+    }
+
+    @Override
+    public SimpleConfig atKey(String key) {
+        return atKey(SimpleConfigOrigin.newSimple("atKey(" + key + ")"), key);
+    }
+
+    @Override
+    public Config atPath(String pathExpression) {
+        SimpleConfigOrigin origin = SimpleConfigOrigin.newSimple("atPath(" + pathExpression + ")");
+        Path path = Path.newPath(pathExpression);
+        Path parent = path.parent();
+        SimpleConfig result = atKey(origin, path.last());
+        while (parent != null) {
+            String key = parent.last();
+            result = result.atKey(origin, key);
+            parent = parent.parent();
+        }
+        return result;
+    }
 }

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

@@ -846,6 +846,20 @@ final class SimpleConfig implements Config, MergeableValue, Serializable {
         return new SimpleConfig(root().withoutPath(path));
     }
 
+    SimpleConfig atKey(ConfigOrigin origin, String key) {
+        return root().atKey(origin, key);
+    }
+
+    @Override
+    public SimpleConfig atKey(String key) {
+        return root().atKey(key);
+    }
+
+    @Override
+    public Config atPath(String path) {
+        return root().atPath(path);
+    }
+
     // serialization all goes through SerializedConfigValue
     private Object writeReplace() throws ObjectStreamException {
         return new SerializedConfigValue(this);

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

@@ -14,6 +14,7 @@ import com.typesafe.config.ConfigList
 import com.typesafe.config.ConfigException
 import com.typesafe.config.ConfigValueType
 import com.typesafe.config.ConfigOrigin
+import com.typesafe.config.ConfigValueFactory
 
 class ConfigValueTest extends TestUtils {
 
@@ -751,6 +752,42 @@ class ConfigValueTest extends TestUtils {
         assertEquals(ResolveStatus.RESOLVED, obj.withoutKey("a").withoutKey("b").resolveStatus())
     }
 
+    @Test
+    def atPathWorksOneElement() {
+        val v = ConfigValueFactory.fromAnyRef(42)
+        val config = v.atPath("a")
+        assertEquals(parseConfig("a=42"), config)
+        assertTrue(config.getValue("a") eq v)
+        assertTrue(config.origin.description.contains("atPath"))
+    }
+
+    @Test
+    def atPathWorksTwoElements() {
+        val v = ConfigValueFactory.fromAnyRef(42)
+        val config = v.atPath("a.b")
+        assertEquals(parseConfig("a.b=42"), config)
+        assertTrue(config.getValue("a.b") eq v)
+        assertTrue(config.origin.description.contains("atPath"))
+    }
+
+    @Test
+    def atPathWorksFourElements() {
+        val v = ConfigValueFactory.fromAnyRef(42)
+        val config = v.atPath("a.b.c.d")
+        assertEquals(parseConfig("a.b.c.d=42"), config)
+        assertTrue(config.getValue("a.b.c.d") eq v)
+        assertTrue(config.origin.description.contains("atPath"))
+    }
+
+    @Test
+    def atKeyWorks() {
+        val v = ConfigValueFactory.fromAnyRef(42)
+        val config = v.atKey("a")
+        assertEquals(parseConfig("a=42"), config)
+        assertTrue(config.getValue("a") eq v)
+        assertTrue(config.origin.description.contains("atKey"))
+    }
+
     @Test
     def configOriginsInSerialization() {
         import scala.collection.JavaConverters._