Add cpython repository into primer runs

- cpython tests is probably the best repo for black to test on as the stdlib's unittests should use all syntax
  - Limit to running in recent versions of the python runtime - e.g. today >= 3.9
    - This allows us to parse more syntax
- Exclude all failing files for now
  - Definately have bugs to explore there - Refer to #2407 for more details there
  - Some test files on purpose have syntax errors, so we will never be able to parse them
- Add new black command arguments logging in debug mode; very handy for seeing how CLI arguments are formatted

cython now succeeds ignoring 16 files:
```
Oh no! 💥 💔 💥
1859 files would be reformatted, 148 files would be left unchanged.
```

Testing
- Ran locally with and without string processing - Very little runtime difference BUT 3 more failed files
```
time /tmp/tb/bin/black --experimental-string-processing --check . 2>&1 | tee /tmp/black_cpython_esp
...
Oh no! 💥 💔 💥
1859 files would be reformatted, 148 files would be left unchanged, 16 files would fail to reformat.

real	4m8.563s
user	16m21.735s
sys	0m6.000s
```
- Add unittest for new covienence config file flattening that allows long arguments to be broke up into an array/list of strings

Addresses #2407

src/black_primer/lib.py

@@ -12,7 +12,17 @@
 from subprocess import CalledProcessError
 from sys import version_info
 from tempfile import TemporaryDirectory
-from typing import Any, Callable, Dict, NamedTuple, Optional, Sequence, Tuple
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    List,
+    NamedTuple,
+    Optional,
+    Sequence,
+    Tuple,
+    Union,
+)
 from urllib.parse import urlparse
 
 import click
@@ -113,6 +123,23 @@ def analyze_results(project_count: int, results: Results) -> int:
     return results.stats["failed"]
 
 
+def _flatten_cli_args(cli_args: List[Union[Sequence[str], str]]) -> List[str]:
+    """Allow a user to put long arguments into a list of strs
+    to make the JSON human readable"""
+    flat_args = []
+    for arg in cli_args:
+        if isinstance(arg, str):
+            flat_args.append(arg)
+            continue
+
+        new_args_str = ""
+        for arg_str in arg:
+            new_args_str += arg_str
+        flat_args.append(new_args_str)
+
+    return flat_args
+
+
 async def black_run(
     project_name: str,
     repo_path: Optional[Path],
@@ -131,7 +158,7 @@ async def black_run(
     stdin_test = project_name.upper() == "STDIN"
     cmd = [str(which(BLACK_BINARY))]
     if "cli_arguments" in project_config and project_config["cli_arguments"]:
-        cmd.extend(project_config["cli_arguments"])
+        cmd.extend(_flatten_cli_args(project_config["cli_arguments"]))
     cmd.append("--check")
     if not no_diff:
         cmd.append("--diff")
@@ -154,6 +181,7 @@ async def black_run(
 
         cwd_path = repo_path.parent if stdin_test else repo_path
         try:
+            LOG.debug(f"Running black for {project_name}: {' '.join(cmd)}")
             _stdout, _stderr = await _gen_check_output(
                 cmd, cwd=cwd_path, env=env, stdin=stdin
             )

src/black_primer/primer.json

@@ -36,6 +36,34 @@
       "long_checkout": false,
       "py_versions": ["all"]
     },
+    "cpython": {
+      "cli_arguments": [
+        "--experimental-string-processing",
+        "--extend-exclude",
+        [
+          "Lib/lib2to3/tests/data/different_encoding.py",
+          "|Lib/lib2to3/tests/data/false_encoding.py",
+          "|Lib/lib2to3/tests/data/py2_test_grammar.py",
+          "|Lib/test/bad_coding.py",
+          "|Lib/test/bad_coding2.py",
+          "|Lib/test/badsyntax_3131.py",
+          "|Lib/test/badsyntax_pep3120.py",
+          "|Lib/test/test_base64.py",
+          "|Lib/test/test_exceptions.py",
+          "|Lib/test/test_grammar.py",
+          "|Lib/test/test_named_expressions.py",
+          "|Lib/test/test_patma.py",
+          "|Lib/test/test_tokenize.py",
+          "|Lib/test/test_xml_etree.py",
+          "|Lib/traceback.py",
+          "|Tools/c-analyzer/c_parser/parser/_delim.py"
+        ]
+      ],
+      "expect_formatting_changes": true,
+      "git_clone_url": "https://github.com/python/cpython.git",
+      "long_checkout": false,
+      "py_versions": ["3.9", "3.10"]
+    },
     "django": {
       "cli_arguments": [
         "--experimental-string-processing",

tests/test_primer.py

@@ -146,6 +146,11 @@ def test_black_run(self) -> None:
             )
         self.assertEqual(2, results.stats["failed"])
 
+    def test_flatten_cli_args(self) -> None:
+        fake_long_args = ["--arg", ["really/", "|long", "|regex", "|splitup"], "--done"]
+        expected = ["--arg", "really/|long|regex|splitup", "--done"]
+        self.assertEqual(expected, lib._flatten_cli_args(fake_long_args))
+
     @event_loop()
     def test_gen_check_output(self) -> None:
         loop = asyncio.get_event_loop()
@@ -184,6 +189,8 @@ def test_git_checkout_or_rebase(self) -> None:
     @patch("sys.stdout", new_callable=StringIO)
     @event_loop()
     def test_process_queue(self, mock_stdout: Mock) -> None:
+        """Test the process queue on primer itself
+        - If you have non black conforming formatting in primer itself this can fail"""
         loop = asyncio.get_event_loop()
         config_path = Path(lib.__file__).parent / "primer.json"
         with patch("black_primer.lib.git_checkout_or_rebase", return_false):