Don't generate files without model (#2044)

Remove unused imports if there are no models in a module.

Once the unused imports are skipped, don't create the file if there
is nothing left in it, unless its `__init__.py`.

datamodel_code_generator/parser/base.py

@@ -1404,22 +1404,24 @@ class Processed(NamedTuple):
 
         for module, models, init, imports, scoped_model_resolver in processed_models:
             result: List[str] = []
-            if with_import:
-                result += [str(self.imports), str(imports), '\n']
-
-            code = dump_templates(models)
-            result += [code]
-
-            if self.dump_resolve_reference_action is not None:
-                result += [
-                    '\n',
-                    self.dump_resolve_reference_action(
-                        m.reference.short_name
-                        for m in models
-                        if m.path in require_update_action_models
-                    ),
-                ]
-
+            if models:
+                if with_import:
+                    result += [str(self.imports), str(imports), '\n']
+
+                code = dump_templates(models)
+                result += [code]
+
+                if self.dump_resolve_reference_action is not None:
+                    result += [
+                        '\n',
+                        self.dump_resolve_reference_action(
+                            m.reference.short_name
+                            for m in models
+                            if m.path in require_update_action_models
+                        ),
+                    ]
+            if not result and not init:
+                continue
             body = '\n'.join(result)
             if code_formatter:
                 body = code_formatter.format_code(body)

tests/data/expected/main/jsonschema/nested_skip/a/__init__.py

@@ -1,5 +1,3 @@
 # generated by datamodel-codegen:
 #   filename:  nested_skip.json
 #   timestamp: 2019-07-26T00:00:00+00:00
-
-from __future__ import annotations

tests/data/expected/main/jsonschema/nested_skip/a/b/__init__.py

@@ -1,5 +1,3 @@
 # generated by datamodel-codegen:
 #   filename:  nested_skip.json
 #   timestamp: 2019-07-26T00:00:00+00:00
-
-from __future__ import annotations

tests/data/expected/main/jsonschema/nested_skip/a/b/c/__init__.py

@@ -1,5 +1,3 @@
 # generated by datamodel-codegen:
 #   filename:  nested_skip.json
 #   timestamp: 2019-07-26T00:00:00+00:00
-
-from __future__ import annotations

tests/data/jsonschema/external_collapse/child.json

@@ -0,0 +1,4 @@
+{
+    "$schema": "http://json-schema.org/draft/2019-09/schema#",
+    "type": "string"
+}

tests/data/jsonschema/external_collapse/parent.json

@@ -0,0 +1,6 @@
+{
+    "$schema": "http://json-schema.org/draft/2019-09/schema#",
+    "properties": {
+        "item":  {"$ref": "child.json"}
+    }
+}

tests/main/jsonschema/test_main_jsonschema.py

@@ -294,6 +294,28 @@ def test_main_jsonschema_multiple_files():
             assert result == path.read_text()
 
 
+@pytest.mark.benchmark
+@freeze_time('2019-07-26')
+def test_main_jsonschema_no_empty_collapsed_external_model():
+    with TemporaryDirectory() as output_dir:
+        output_dir: Path = Path(output_dir) / 'output'
+        output_dir.mkdir()
+        return_code: Exit = main(
+            [
+                '--input',
+                str(JSON_SCHEMA_DATA_PATH / 'external_collapse'),
+                '--output',
+                str(output_dir),
+                '--input-file-type',
+                'jsonschema',
+                '--collapse-root-models',
+            ]
+        )
+        assert return_code == Exit.OK
+        assert not (output_dir / 'child.py').exists()
+        assert (output_dir / '__init__.py').exists()
+
+
 @pytest.mark.parametrize(
     'output_model,expected_output',
     [