Alembic import: changing cache modifier path no longer discards object paths

This allows, for example, the path of an Alembic file to be changed from
absolute to relative, without having to reconstruct all object paths.

tests/python/bl_alembic_import_test.py

@@ -85,6 +85,43 @@ class SimpleImportTest(unittest.TestCase):
         for ob in bpy.data.objects:
             self.assertEqual('Cube' in ob.name, ob.select)
 
+    def test_change_path(self):
+        import math
+
+        fname = 'cube-rotating1.abc'
+        abc = self.testdir / fname
+        relpath = bpy.path.relpath(str(abc))
+
+        res = bpy.ops.wm.alembic_import(filepath=str(abc), as_background_job=False)
+        self.assertEqual({'FINISHED'}, res)
+        cube = bpy.context.active_object
+
+        # Check that the file loaded ok.
+        bpy.context.scene.frame_set(10)
+        x, y, z = cube.matrix_world.to_euler('XYZ')
+        self.assertAlmostEqual(x, 0)
+        self.assertAlmostEqual(y, 0)
+        self.assertAlmostEqual(z, math.pi / 2, places=5)
+
+        # Change path from absolute to relative. This should not break the animation.
+        bpy.context.scene.frame_set(1)
+        bpy.data.cache_files[fname].filepath = relpath
+        bpy.context.scene.frame_set(10)
+
+        x, y, z = cube.matrix_world.to_euler('XYZ')
+        self.assertAlmostEqual(x, 0)
+        self.assertAlmostEqual(y, 0)
+        self.assertAlmostEqual(z, math.pi / 2, places=5)
+
+        # Replace the Alembic file; this should apply new animation.
+        bpy.data.cache_files[fname].filepath = relpath.replace('1.abc', '2.abc')
+        bpy.context.scene.update()
+
+        x, y, z = cube.matrix_world.to_euler('XYZ')
+        self.assertAlmostEqual(x, math.pi / 2, places=5)
+        self.assertAlmostEqual(y, 0)
+        self.assertAlmostEqual(z, 0)
+
 
 def main():
     global args