Add custom formatters (#1733)

* Support custom formatters for CodeFormatter

* Add custom formatters argument

* Add graphql to docs/supported-data-types.md

* Add test

custom formatter for custom-scalar-types.graphql;

* Run poetry run scripts/format.sh

* Add simple doc

docs/custom-formatters.md

@@ -0,0 +1,23 @@
+# Custom Code Formatters
+
+New features of the `datamodel-code-generator` it is custom code formatters.
+
+## Usage
+To use the `--custom-formatters` option, you'll need to pass the module with your formatter. For example
+
+**your_module.py**
+```python
+from datamodel_code_generator.format import CustomCodeFormatter
+
+class CodeFormatter(CustomCodeFormatter):
+    def apply(self, code: str) -> str:
+        # processed code
+        return ...       
+
+```
+
+and run the following command
+
+```sh
+$ datamodel-codegen --input {your_input_file} --output {your_output_file} --custom-formatters "{path_to_your_module}.your_module"
+```

docs/index.md

@@ -435,8 +435,11 @@ Template customization:
                         Wrap string literal by using black `experimental-
                         string-processing` option (require black 20.8b0 or
                         later)
-  --additional-imports  Custom imports for output (delimited list input)
-
+  --additional-imports  Custom imports for output (delimited list input).
+                        For example "datetime.date,datetime.datetime"
+  --custom-formatters   List of modules with custom formatter (delimited list input).
+  --custom-formatters-kwargs A file with kwargs for custom formatters.
+  
 OpenAPI-only options:
   --openapi-scopes {schemas,paths,tags,parameters} [{schemas,paths,tags,parameters} ...]
                         Scopes of OpenAPI model generation (default: schemas)

docs/supported-data-types.md

@@ -6,6 +6,7 @@ This code generator supports the following input formats:
 - JSON Schema ([JSON Schema Core](http://json-schema.org/draft/2019-09/json-schema-validation.html) /[JSON Schema Validation](http://json-schema.org/draft/2019-09/json-schema-validation.html))
 - JSON/YAML Data (it will be converted to JSON Schema)
 - Python dictionary (it will be converted to JSON Schema)
+- GraphQL schema ([GraphQL Schemas and Types](https://graphql.org/learn/schema/))
 
 ## Implemented data types and features