Make impossible to merge two schema definitions that are pointing to …

…a different entry

src/core/etl/src/Flow/ETL/Row/Schema/Definition.php

@@ -17,6 +17,7 @@
 use function Flow\ETL\DSL\type_xml;
 use function Flow\ETL\DSL\type_xml_node;
 use Flow\ETL\Exception\InvalidArgumentException;
+use Flow\ETL\Exception\RuntimeException;
 use Flow\ETL\PHP\Type\Logical\ListType;
 use Flow\ETL\PHP\Type\Logical\MapType;
 use Flow\ETL\PHP\Type\Logical\StructureType;
@@ -239,6 +240,10 @@ public function matches(Entry $entry) : bool
 
     public function merge(self $definition) : self
     {
+        if (!$this->ref->is($definition->ref)) {
+            throw new RuntimeException(\sprintf('Cannot merge different definitions, %s and %s', $this->ref->name(), $definition->ref->name()));
+        }
+
         $constraint = new Any($this->constraint, $definition->constraint);
 
         if ($this->constraint instanceof VoidConstraint) {

src/core/etl/tests/Flow/ETL/Tests/Unit/Row/Schema/DefinitionTest.php

@@ -17,6 +17,7 @@
 use function Flow\ETL\DSL\type_map;
 use function Flow\ETL\DSL\type_string;
 use Flow\ETL\Exception\InvalidArgumentException;
+use Flow\ETL\Exception\RuntimeException;
 use Flow\ETL\PHP\Type\Logical\List\ListElement;
 use Flow\ETL\PHP\Type\Logical\ListType;
 use Flow\ETL\PHP\Type\Logical\StructureType;
@@ -170,6 +171,14 @@ public function test_merging_anything_with_null() : void
         );
     }
 
+    public function test_merging_different_entries() : void
+    {
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Cannot merge different definitions, int and string');
+
+        Definition::integer('int')->merge(Definition::string('string'));
+    }
+
     public function test_merging_numeric_types() : void
     {
         $this->assertEquals(