Fix type annotations on template decorators (#1211)

**Pull Request Checklist**
- [X] Fixes #1182
- [X] Tests added
- [ ] Documentation/examples added
- [X] [Good commit messages](https://cbea.ms/git-commit/) and/or PR
title

**Description of PR**
Currently, mypy raises a `misc` error when using a decorator from
`TemplateDecoratorFuncsMixin`, complaining that the method "does not
accept self argument".

This PR uses `Concatenate` to add the missing parameter.

Signed-off-by: Alice Purcell <alicederyn@gmail.com>

src/hera/workflows/_meta_mixins.py

@@ -13,14 +13,15 @@
 if sys.version_info >= (3, 10):
     from inspect import get_annotations
     from types import NoneType
+    from typing import Concatenate, ParamSpec
 else:
+    from typing_extensions import Concatenate, ParamSpec
+
     from hera.shared._inspect import get_annotations
 
     NoneType = type(None)
 
 
-from typing_extensions import ParamSpec
-
 from hera.shared import BaseMixin, global_config
 from hera.shared._global_config import _DECORATOR_SYNTAX_FLAG, _flag_enabled
 from hera.shared._pydantic import BaseModel, get_fields, root_validator
@@ -474,7 +475,10 @@ def _add_type_hints(
 ) -> Callable[
     ...,
     Callable[
-        PydanticKwargs,  # this adds type hints to the underlying *library* function kwargs
+        Concatenate[
+            object,  # this is the `self` parameter
+            PydanticKwargs,  # this adds type hints to the underlying *library* function kwargs
+        ],
         Callable[  # we will return a function that is a decorator
             [Callable[FuncIns, FuncR]],  # taking underlying *user* function
             Callable[FuncIns, FuncR],  # and returning it

tests/typehints/test_template_decorator.py

@@ -0,0 +1,50 @@
+from pathlib import Path
+from subprocess import run
+from tempfile import TemporaryDirectory
+from textwrap import dedent
+
+COMMON_SETUP = """
+from hera.shared import global_config
+from hera.workflows import Input, Output, Workflow
+
+w = Workflow()
+
+"""
+
+
+def run_mypy(python_code: str):
+    with TemporaryDirectory() as d:
+        python_file = Path(d) / "example.py"
+        python_file.write_text(python_code)
+        mypy_cmd = ["mypy", "--config-file", "tests/typehints/test-mypy.toml", str(python_file)]
+        result = run(mypy_cmd, check=False, capture_output=True, encoding="utf-8")
+        if result.returncode != 0:
+            msg = f"Error calling {' '.join(mypy_cmd)}:\n{result.stderr}{result.stdout}"
+            raise AssertionError(msg)
+        return result.stdout.replace(d, "")
+
+
+def test_script_decoration_no_arguments():
+    """Verify a script can be decorated with no extra arguments."""
+    SCRIPT = """
+        @w.script()
+        def simple_script(_: Input) -> Output:
+            return Output()
+
+        reveal_type(simple_script(Input()))
+    """
+    result = run_mypy(COMMON_SETUP + dedent(SCRIPT))
+    assert 'Revealed type is "hera.workflows.io.v2.Output"' in result
+
+
+def test_script_decoration_accepts_name_argument():
+    """Verify the script decorator can be passed a name."""
+    SCRIPT = """
+        @w.script(name = "some_script")
+        def simple_script(_: Input) -> Output:
+            return Output()
+
+        reveal_type(simple_script(Input()))
+    """
+    result = run_mypy(COMMON_SETUP + dedent(SCRIPT))
+    assert 'Revealed type is "hera.workflows.io.v2.Output"' in result