do a better job with origin when there's an empty config. add Config.empty().

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

@@ -69,6 +69,10 @@ public final class Config {
         return ConfigImpl.emptyRoot(rootPath);
     }
 
+    public static ConfigObject empty() {
+        return ConfigImpl.empty();
+    }
+
     public static ConfigRoot systemPropertiesRoot(String rootPath) {
         return ConfigImpl.systemPropertiesRoot(rootPath);
     }

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

@@ -233,19 +233,40 @@ abstract class AbstractConfigObject extends AbstractConfigValue implements
         if (stack.isEmpty())
             throw new ConfigException.BugOrBroken(
                     "can't merge origins on empty list");
+        final String prefix = "merge of ";
         StringBuilder sb = new StringBuilder();
-        String prefix = "merge of ";
-        sb.append(prefix);
+        ConfigOrigin firstOrigin = null;
+        int numMerged = 0;
         for (AbstractConfigValue v : stack) {
+            if (firstOrigin == null)
+                firstOrigin = v.origin();
+
             String desc = v.origin().description();
             if (desc.startsWith(prefix))
                 desc = desc.substring(prefix.length());
+
+            if (v instanceof ConfigObject && ((ConfigObject) v).isEmpty()) {
+                // don't include empty files or the .empty()
+                // config in the description, since they are
+                // likely to be "implementation details"
+            } else {
                 sb.append(desc);
                 sb.append(",");
+                numMerged += 1;
             }
+        }
+        if (numMerged > 0) {
             sb.setLength(sb.length() - 1); // chop comma
+            if (numMerged > 1) {
+                return new SimpleConfigOrigin(prefix + sb.toString());
+            } else {
                 return new SimpleConfigOrigin(sb.toString());
             }
+        } else {
+            // the configs were all empty.
+            return firstOrigin;
+        }
+    }
 
     static ConfigOrigin mergeOrigins(AbstractConfigObject... stack) {
         return mergeOrigins(Arrays.asList(stack));

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

@@ -160,7 +160,13 @@ public class ConfigImpl {
 
     /** For use ONLY by library internals, DO NOT TOUCH not guaranteed ABI */
     public static ConfigRoot emptyRoot(String rootPath) {
-        return SimpleConfigObject.empty().asRoot(Parser.parsePath(rootPath));
+        return SimpleConfigObject.empty(new SimpleConfigOrigin(rootPath))
+                .asRoot(
+                Parser.parsePath(rootPath));
+    }
+
+    public static ConfigObject empty() {
+        return SimpleConfigObject.empty();
     }
 
     /** For use ONLY by library internals, DO NOT TOUCH not guaranteed ABI */

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

@@ -113,8 +113,10 @@ final class SimpleConfigObject extends AbstractConfigObject {
         return new HashSet<ConfigValue>(value.values());
     }
 
+    final static String EMPTY_NAME = "empty config";
+
     final static SimpleConfigObject empty() {
-        return new SimpleConfigObject(new SimpleConfigOrigin("empty config"),
+        return new SimpleConfigObject(new SimpleConfigOrigin(EMPTY_NAME),
                 Collections.<String, AbstractConfigValue> emptyMap());
     }
 

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

@@ -9,6 +9,7 @@ import com.typesafe.config.ConfigObject
 import com.typesafe.config.ConfigList
 import com.typesafe.config.ConfigException
 import com.typesafe.config.ConfigValueType
+import com.typesafe.config.ConfigOrigin
 
 class ConfigValueTest extends TestUtils {
 
@@ -330,4 +331,31 @@ class ConfigValueTest extends TestUtils {
         assertEquals(Seq(a, b, c, d) map { "xx " + _ + " yy" },
             Seq("a", "b", "c", "d") map { obj2.getString(_) })
     }
+
+    @Test
+    def mergeOriginsWorks() {
+        def o(desc: String, empty: Boolean) = {
+            val values = new java.util.HashMap[String, AbstractConfigValue]()
+            if (!empty)
+                values.put("hello", intValue(37))
+            new SimpleConfigObject(new SimpleConfigOrigin(desc), values);
+        }
+        def m(values: AbstractConfigObject*) = {
+            AbstractConfigObject.mergeOrigins(values: _*).description()
+        }
+
+        // simplest case
+        assertEquals("merge of a,b", m(o("a", false), o("b", false)))
+        // combine duplicate "merge of"
+        assertEquals("merge of a,x,y", m(o("a", false), o("merge of x,y", false)))
+        assertEquals("merge of a,b,x,y", m(o("merge of a,b", false), o("merge of x,y", false)))
+        // ignore empty objects
+        assertEquals("a", m(o("foo", true), o("a", false)))
+        // unless they are all empty, pick the first one
+        assertEquals("foo", m(o("foo", true), o("a", true)))
+        // merge just one
+        assertEquals("foo", m(o("foo", false)))
+        // merge three
+        assertEquals("merge of a,b,c", m(o("a", false), o("b", false), o("c", false)))
+    }
 }