Add no-redundant-dataclasses pre-commit hook

.pre-commit-hooks.yaml

@@ -0,0 +1,6 @@
+-   id: no-redundant-dataclasses
+    name: No redundant dataclasses
+    description: Prevents using raw dataclasses on Strawberry GraphQL types
+    entry: pre-commit-no-redundant-dataclasses
+    language: python
+    types: [python]

RELEASE.md

@@ -0,0 +1,15 @@
+Release type: minor
+
+Add a [pre-commit](https://pre-commit.com/) hook to prevent redundant `@dataclass` decorators on Strawberry types.
+
+Since Strawberry types (`@strawberry.type`, `@strawberry.input`, `@strawberry.interface`) already provide dataclass functionality, decorating them with `@dataclass` is redundant. This hook detects and prevents this pattern, helping maintain cleaner code.
+
+To use the hook, add it to your `.pre-commit-config.yaml`:
+
+```yaml
+repos:
+  - repo: https://github.com/strawberry-graphql/strawberry
+    rev: <version>
+    hooks:
+      - id: no-redundant-dataclasses
+```

pyproject.toml

@@ -35,6 +35,7 @@ documentation = "https://strawberry.rocks/"
 
 [project.scripts]
 strawberry = "strawberry.cli:run"
+pre-commit-no-redundant-dataclasses = "strawberry.hooks.no_redundant_dataclasses:main"
 
 [project.optional-dependencies]
 aiohttp = ["aiohttp>=3.7.4.post0,<4"]
@@ -342,6 +343,7 @@ ignore = [
 "strawberry/extensions/tracing/__init__.py" = ["TCH004"]
 "strawberry/fastapi/*" = ["B008"]
 "strawberry/annotation.py" = ["RET505"]
+"strawberry/hooks/*" = ["T201"]
 "tests/*" = [
   "ANN001",
   "ANN201",

strawberry/hooks/no_redundant_dataclasses.py

@@ -0,0 +1,77 @@
+from __future__ import annotations
+
+import argparse
+import ast
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+
+class Visitor(ast.NodeVisitor):
+    """A linter that finds issues and includes the source code."""
+
+    def __init__(self) -> None:
+        self.errors: list[str] = []
+
+    def visit_ClassDef(self, node: ast.ClassDef) -> None:
+        is_strawberry_class = False
+        is_raw_dataclass = False
+
+        for decorator in node.decorator_list:
+            # Check for strawberry decorators: type, input, interface
+            if (
+                isinstance(decorator, ast.Attribute)
+                and isinstance(decorator.value, ast.Name)
+                and decorator.value.id == "strawberry"
+                and decorator.attr in ("type", "input", "interface")
+            ) or (
+                isinstance(decorator, ast.Call)
+                and isinstance(decorator.func, ast.Attribute)
+                and isinstance(decorator.func.value, ast.Name)
+                and decorator.func.value.id == "strawberry"
+                and decorator.func.attr in ("type", "input", "interface")
+            ):
+                is_strawberry_class = True
+
+            if (isinstance(decorator, ast.Name) and decorator.id == "dataclass") or (
+                isinstance(decorator, ast.Attribute)
+                and isinstance(decorator.value, ast.Name)
+                and decorator.value.id == "dataclasses"
+                and decorator.attr == "dataclass"
+            ):
+                is_raw_dataclass = True
+
+        if is_strawberry_class and is_raw_dataclass:
+            self.errors.append(f":{node.lineno}: {node.name}")
+
+        self.generic_visit(node)
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("filenames", nargs="*")
+    args = parser.parse_args(argv)
+    violations: list[str] = []
+
+    for filename in args.filenames:
+        with Path(filename).open("rb") as f:
+            tree = ast.parse(f.read(), filename=filename)
+            visitor = Visitor()
+            visitor.visit(tree)
+            violations.extend(f"- {filename}{error}" for error in visitor.errors)
+
+    if not violations:
+        return 0
+
+    msg = "\n".join(
+        (
+            "Decorating strawberry types with dataclasses.dataclass is redundant.",
+            "Remove the dataclass decorator from the following classes:",
+            *violations,
+        )
+    )
+
+    print(msg)
+    return 1

tests/hooks/test_no_redundant_dataclasses.py

@@ -0,0 +1,46 @@
+from textwrap import dedent
+
+from strawberry.hooks.no_redundant_dataclasses import main
+
+
+def test_check_namespaced_decorator(tmp_path):
+    code = """
+    import strawberry
+    import dataclasses
+
+    @dataclasses.dataclass
+    @strawberry.type
+    class Foo: ...
+    """
+    file = tmp_path / "foo.py"
+    file.write_text(dedent(code), encoding="utf-8")
+    exit_code = main([str(file)])
+    assert exit_code == 1
+
+
+def test_check_imported_decorator(tmp_path):
+    code = """
+    import strawberry
+    from dataclasses import dataclass
+
+    @dataclass
+    @strawberry.type
+    class Foo: ...
+    """
+    file = tmp_path / "foo.py"
+    file.write_text(dedent(code), encoding="utf-8")
+    exit_code = main([str(file)])
+    assert exit_code == 1
+
+
+def test_check_passing_file(tmp_path):
+    code = """
+    import strawberry
+
+    @strawberry.type
+    class Foo: ...
+    """
+    file = tmp_path / "foo.py"
+    file.write_text(dedent(code), encoding="utf-8")
+    exit_code = main([str(file)])
+    assert exit_code == 0