[fix] Only map nodes of the exact same type #57

src/main/java/se/kth/spork/spoon/SpoonMapping.java

@@ -62,7 +62,10 @@ public static SpoonMapping fromGumTreeMapping(MappingStore gumtreeMapping) {
                     throw new IllegalStateException("non-root node " + m.first.toShortString()
                             + " had no mapped Spoon object");
                 }
-            } else {
+            } else if (spoonSrc.getClass() == spoonDst.getClass()) {
+                // It is important to only map nodes of the exact same type, as 3DM has no notion of "correct"
+                // parent-child relationships. Mapping e.g. an array type reference to a non-array type reference
+                // may cause the resulting merge to try to treat either as the other, which does not work out.
                 mapping.put(spoonSrc, spoonDst);
             }
         }

src/test/resources/clean/left_modified/modify_array_type/Base.java

@@ -0,0 +1,3 @@
+class Cls {
+    private Integer[] arr;
+}

src/test/resources/clean/left_modified/modify_array_type/Expected.java

@@ -0,0 +1,3 @@
+class Cls {
+    private Object arr;
+}

src/test/resources/clean/left_modified/modify_array_type/Left.java

@@ -0,0 +1,3 @@
+class Cls {
+    private Object arr;
+}

src/test/resources/clean/left_modified/modify_array_type/Right.java

@@ -0,0 +1,3 @@
+class Cls {
+    private Integer[] arr;
+}