Move ``PYLINTHOME`` to constants and test it (#6509)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/pylint/constants.py b/pylint/constants.py
index 90e2b734e..6986b8a4e 100644
--- a/pylint/constants.py
+++ b/pylint/constants.py
@@ -5,8 +5,10 @@
 from __future__ import annotations
 
 import os
+import pathlib
 import platform
 import sys
+from datetime import datetime
 from typing import NamedTuple
 
 import astroid
@@ -209,3 +211,58 @@ INCOMPATIBLE_WITH_USELESS_SUPPRESSION = frozenset(
 
 
 TYPING_TYPE_CHECKS_GUARDS = frozenset({"typing.TYPE_CHECKING", "TYPE_CHECKING"})
+
+
+def _warn_about_old_home(pylint_home: pathlib.Path) -> None:
+    """Warn users about the old pylint home being deprecated.
+
+    The spam prevention mechanism is due to pylint being used in parallel by
+    pre-commit, and the message being spammy in this context
+    Also if you work with an old version of pylint that recreates the
+    old pylint home, you can get the old message for a long time.
+    """
+    prefix_spam_prevention = "pylint_warned_about_old_cache_already"
+    spam_prevention_file = pathlib.Path(pylint_home) / datetime.now().strftime(
+        prefix_spam_prevention + "_%Y-%m-%d.temp"
+    )
+    old_home = pathlib.Path(USER_HOME) / OLD_DEFAULT_PYLINT_HOME
+
+    if old_home.exists() and not spam_prevention_file.exists():
+        print(
+            f"PYLINTHOME is now '{pylint_home}' but obsolescent '{old_home}' is found; "
+            "you can safely remove the latter",
+            file=sys.stderr,
+        )
+
+        # Remove old spam prevention file
+        if pylint_home.exists():
+            for filename in pylint_home.iterdir():
+                if prefix_spam_prevention in str(filename):
+                    try:
+                        os.remove(pylint_home / filename)
+                    except OSError:  # pragma: no cover
+                        pass
+
+        # Create spam prevention file for today
+        try:
+            pylint_home.mkdir(parents=True, exist_ok=True)
+            with open(spam_prevention_file, "w", encoding="utf8") as f:
+                f.write("")
+        except Exception as exc:  # pragma: no cover  # pylint: disable=broad-except
+            print(
+                "Can't write the file that was supposed to "
+                f"prevent 'pylint.d' deprecation spam in {pylint_home} because of {exc}."
+            )
+
+
+def _get_pylint_home() -> str:
+    """Return the pylint home."""
+    if "PYLINTHOME" in os.environ:
+        return os.environ["PYLINTHOME"]
+
+    _warn_about_old_home(pathlib.Path(DEFAULT_PYLINT_HOME))
+
+    return DEFAULT_PYLINT_HOME
+
+
+PYLINT_HOME = _get_pylint_home()