Adhere to XDG specification for cache dir.

pre_commit/commands/clean.py

@@ -8,7 +8,9 @@ from pre_commit.util import rmtree
 
 
 def clean(runner):
-    if os.path.exists(runner.store.directory):
-        rmtree(runner.store.directory)
-        output.write_line('Cleaned {}.'.format(runner.store.directory))
+    legacy_path = os.path.expanduser('~/.pre-commit')
+    for directory in (runner.store.directory, legacy_path):
+        if os.path.exists(directory):
+            rmtree(directory)
+            output.write_line('Cleaned {}.'.format(directory))
     return 0

pre_commit/error_handler.py

@@ -28,10 +28,11 @@ def _log_and_exit(msg, exc, formatted):
         _to_bytes(exc), b'\n',
     ))
     output.write(error_msg)
-    output.write_line('Check the log at ~/.pre-commit/pre-commit.log')
     store = Store()
     store.require_created()
-    with open(os.path.join(store.directory, 'pre-commit.log'), 'wb') as log:
+    log_path = os.path.join(store.directory, 'pre-commit.log')
+    output.write_line('Check the log at {}'.format(log_path))
+    with open(log_path, 'wb') as log:
         output.write(error_msg, stream=log)
         output.write_line(formatted, stream=log)
     raise SystemExit(1)

pre_commit/store.py

@@ -29,9 +29,9 @@ def _get_default_directory():
     `Store.get_default_directory` can be mocked in tests and
     `_get_default_directory` can be tested.
     """
-    return os.environ.get(
-        'PRE_COMMIT_HOME',
-        os.path.join(os.path.expanduser('~'), '.pre-commit'),
+    return os.environ.get('PRE_COMMIT_HOME') or os.path.join(
+        os.environ.get('XDG_CACHE_HOME') or os.path.expanduser('~/.cache'),
+        'pre-commit',
     )