try-except tomllib import (#2987)

See #2965 

I left the version check in place because mypy doesn't generally like try-excepted imports.

CHANGES.md

@@ -39,6 +39,9 @@
 
 <!-- Changes to how Black is packaged, such as dependency requirements -->
 
+- Use `tomli` instead of `tomllib` on Python 3.11 builds where `tomllib` is not
+  available (#2987)
+
 ### Parser
 
 <!-- Changes to the parser or to version autodetection -->

setup.py

@@ -98,7 +98,7 @@ def find_python_files(base: Path) -> List[Path]:
     install_requires=[
         "click>=8.0.0",
         "platformdirs>=2",
-        "tomli>=1.1.0; python_version < '3.11'",
+        "tomli>=1.1.0; python_full_version < '3.11.0a7'",
         "typed-ast>=1.4.2; python_version < '3.8' and implementation_name == 'cpython'",
         "pathspec>=0.9.0",
         "dataclasses>=0.6; python_version < '3.7'",

src/black/files.py

@@ -22,7 +22,11 @@
 from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
 
 if sys.version_info >= (3, 11):
-    import tomllib
+    try:
+        import tomllib
+    except ImportError:
+        # Help users on older alphas
+        import tomli as tomllib
 else:
     import tomli as tomllib