allow duplicate keys in .conf with later key winning

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

@@ -290,13 +290,25 @@ final class Parser {
 
                     consolidateValueTokens();
                     Token valueToken = nextTokenIgnoringNewline();
+                    AbstractConfigValue newValue = parseValue(valueToken);
 
-                    // note how we handle duplicate keys: the last one just
-                    // wins.
-                    // FIXME in strict JSON, dups should be an error; while in
+                    // In strict JSON, dups should be an error; while in
                     // our custom config language, they should be merged if the
-                    // value is an object.
-                    values.put(key, parseValue(valueToken));
+                    // value is an object (or substitution that could become
+                    // an object).
+                    AbstractConfigValue existing = values.get(key);
+
+                    if (existing != null) {
+                        if (flavor == SyntaxFlavor.JSON) {
+                            throw parseError("JSON does not allow duplicate fields: '"
+                                    + key
+                                    + "' was already seen at "
+                                    + existing.origin().description());
+                        } else {
+                            newValue = newValue.withFallback(existing);
+                        }
+                    }
+                    values.put(key, newValue);
 
                     afterComma = false;
                 } else if (t == Tokens.CLOSE_CURLY) {

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

@@ -116,4 +116,48 @@ class ConfParserTest extends TestUtils {
             parsePath("-")
         }
     }
+
+    @Test
+    def duplicateKeyLastWins() {
+        val obj = parseObject("""{ "a" : 10, "a" : 11 } """)
+
+        assertEquals(1, obj.size())
+        assertEquals(11, obj.getInt("a"))
+    }
+
+    @Test
+    def duplicateKeyObjectsMerged() {
+        val obj = parseObject("""{ "a" : { "x" : 1, "y" : 2 }, "a" : { "x" : 42, "z" : 100 } }""")
+
+        assertEquals(1, obj.size())
+        assertEquals(3, obj.getObject("a").size())
+        assertEquals(42, obj.getInt("a.x"))
+        assertEquals(2, obj.getInt("a.y"))
+        assertEquals(100, obj.getInt("a.z"))
+    }
+
+    @Test
+    def duplicateKeyObjectsMergedRecursively() {
+        val obj = parseObject("""{ "a" : { "b" : { "x" : 1, "y" : 2 } }, "a" : { "b" : { "x" : 42, "z" : 100 } } }""")
+
+        assertEquals(1, obj.size())
+        assertEquals(1, obj.getObject("a").size())
+        assertEquals(3, obj.getObject("a.b").size())
+        assertEquals(42, obj.getInt("a.b.x"))
+        assertEquals(2, obj.getInt("a.b.y"))
+        assertEquals(100, obj.getInt("a.b.z"))
+    }
+
+    @Test
+    def duplicateKeyObjectsMergedRecursivelyDeeper() {
+        val obj = parseObject("""{ "a" : { "b" : { "c" : { "x" : 1, "y" : 2 } } }, "a" : { "b" : { "c" : { "x" : 42, "z" : 100 } } } }""")
+
+        assertEquals(1, obj.size())
+        assertEquals(1, obj.getObject("a").size())
+        assertEquals(1, obj.getObject("a.b").size())
+        assertEquals(3, obj.getObject("a.b.c").size())
+        assertEquals(42, obj.getInt("a.b.c.x"))
+        assertEquals(2, obj.getInt("a.b.c.y"))
+        assertEquals(100, obj.getInt("a.b.c.z"))
+    }
 }

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

@@ -149,7 +149,6 @@ abstract trait TestUtils {
         """{ "foo" : { "bar" : "baz" }, "baz" : "boo" }""",
         """{ "foo" : { "bar" : "baz", "woo" : "w00t" }, "baz" : "boo" }""",
         """{ "foo" : [10,11,12], "baz" : "boo" }""",
-        ParseTest(true, """{ "foo" : "bar", "foo" : "bar2" }"""), // dup keys - lift just returns both, we use last one
         """[{},{},{},{}]""",
         """[[[[[[]]]]]]""",
         """{"a":{"a":{"a":{"a":{"a":{"a":{"a":{"a":42}}}}}}}}""",
@@ -160,6 +159,7 @@ abstract trait TestUtils {
     private val validConfInvalidJson = List[ParseTest](
         """{ "foo" : bar }""", // no quotes on value
         """{ "foo" : null bar 42 baz true 3.14 "hi" }""", // bunch of values to concat into a string
+        ParseTest(true, """{ "foo" : "bar", "foo" : "bar2" }"""), // dup keys - lift just returns both
         "[ foo ]", // not a known token in JSON
         "[ t ]", // start of "true" but ends wrong in JSON
         "[ tx ]",