Add support for pydantic dataclasses (#406)

tests/util.py

@@ -1,7 +1,10 @@
 import asyncio
+import atexit
 import importlib
 import os
+import platform
 import sys
+import tempfile
 from dataclasses import dataclass
 from pathlib import Path
 from types import ModuleType
@@ -22,6 +25,7 @@ root_path = Path(__file__).resolve().parent
 inputs_path = root_path.joinpath("inputs")
 output_path_reference = root_path.joinpath("output_reference")
 output_path_betterproto = root_path.joinpath("output_betterproto")
+output_path_betterproto_pydantic = root_path.joinpath("output_betterproto_pydantic")
 
 
 def get_files(path, suffix: str) -> Generator[str, None, None]:
@@ -36,19 +40,56 @@ def get_directories(path):
 
 
 async def protoc(
-    path: Union[str, Path], output_dir: Union[str, Path], reference: bool = False
+    path: Union[str, Path],
+    output_dir: Union[str, Path],
+    reference: bool = False,
+    pydantic_dataclasses: bool = False,
 ):
     path: Path = Path(path).resolve()
     output_dir: Path = Path(output_dir).resolve()
     python_out_option: str = "python_betterproto_out" if not reference else "python_out"
-    command = [
-        sys.executable,
-        "-m",
-        "grpc.tools.protoc",
-        f"--proto_path={path.as_posix()}",
-        f"--{python_out_option}={output_dir.as_posix()}",
-        *[p.as_posix() for p in path.glob("*.proto")],
-    ]
+
+    if pydantic_dataclasses:
+        plugin_path = Path("src/betterproto/plugin/main.py")
+
+        if "Win" in platform.system():
+            with tempfile.NamedTemporaryFile(
+                "w", encoding="UTF-8", suffix=".bat", delete=False
+            ) as tf:
+                # See https://stackoverflow.com/a/42622705
+                tf.writelines(
+                    [
+                        "@echo off",
+                        f"\nchdir {os.getcwd()}",
+                        f"\n{sys.executable} -u {plugin_path.as_posix()}",
+                    ]
+                )
+
+                tf.flush()
+
+                plugin_path = Path(tf.name)
+                atexit.register(os.remove, plugin_path)
+
+        command = [
+            sys.executable,
+            "-m",
+            "grpc.tools.protoc",
+            f"--plugin=protoc-gen-custom={plugin_path.as_posix()}",
+            "--experimental_allow_proto3_optional",
+            "--custom_opt=pydantic_dataclasses",
+            f"--proto_path={path.as_posix()}",
+            f"--custom_out={output_dir.as_posix()}",
+            *[p.as_posix() for p in path.glob("*.proto")],
+        ]
+    else:
+        command = [
+            sys.executable,
+            "-m",
+            "grpc.tools.protoc",
+            f"--proto_path={path.as_posix()}",
+            f"--{python_out_option}={output_dir.as_posix()}",
+            *[p.as_posix() for p in path.glob("*.proto")],
+        ]
     proc = await asyncio.create_subprocess_exec(
         *command, stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE
     )