Merge pull request #4504 from feuillemorte/4278_add_cachedir_tag

#4278 Added a CACHEDIR.TAG file to the cache directory

src/_pytest/cacheprovider.py

@@ -33,6 +33,13 @@ which provides the `--lf` and `--ff` options, as well as the `cache` fixture.
 See [the docs](https://docs.pytest.org/en/latest/cache.html) for more information.
 """
 
+CACHEDIR_TAG_CONTENT = b"""\
+Signature: 8a477f597d28d172789f06886806bc55
+# This file is a cache directory tag created by pytest.
+# For information about cache directory tags, see:
+#	http://www.bford.info/cachedir/spec.html
+"""
+
 
 @attr.s
 class Cache(object):
@@ -140,6 +147,10 @@ class Cache(object):
                 msg = u"# Created by pytest automatically.\n*"
                 gitignore_path.write_text(msg, encoding="UTF-8")
 
+            cachedir_tag_path = self._cachedir.joinpath("CACHEDIR.TAG")
+            if not cachedir_tag_path.is_file():
+                cachedir_tag_path.write_bytes(CACHEDIR_TAG_CONTENT)
+
 
 class LFPlugin(object):
     """ Plugin which implements the --lf (run last-failing) option """