Add typing to all calls to ``self.stats`` (#4973)

* Add typing to all calls to ``self.stats``

All checkers inherit from a baseclass which has a ``stats`` attribute.
This attribute has a fairly unmanageable type, but the current typing includes all variations of the attribute.
Other changes not directly related to ``self.stats`` are due to ``mypy``warnings.
This incorporate the feedback received in #4954

* Add ``CheckerStatistic`` class to ``pylint/typing``

* Guard `typing.Counter` import

Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/pylint/checkers/__init__.py b/pylint/checkers/__init__.py
index ffc940223..584f476fc 100644
--- a/pylint/checkers/__init__.py
+++ b/pylint/checkers/__init__.py
@@ -46,28 +46,35 @@ messages nor reports. XXX not true, emit a 07 report !
 
 """
 
+from typing import Iterable, List, Union
+
 from pylint.checkers.base_checker import BaseChecker, BaseTokenChecker
 from pylint.checkers.deprecated import DeprecatedMixin
 from pylint.checkers.mapreduce_checker import MapReduceMixin
+from pylint.typing import CheckerStats
 from pylint.utils import diff_string, register_plugins
 
 
-def table_lines_from_stats(stats, old_stats, columns):
+def table_lines_from_stats(
+    stats: CheckerStats,
+    old_stats: CheckerStats,
+    columns: Iterable[str],
+) -> List[str]:
     """get values listed in <columns> from <stats> and <old_stats>,
     and return a formated list of values, designed to be given to a
     ureport.Table object
     """
-    lines = []
+    lines: List[str] = []
     for m_type in columns:
-        new = stats[m_type]
-        old = old_stats.get(m_type)
+        new: Union[int, str] = stats[m_type]  # type: ignore
+        old: Union[int, str, None] = old_stats.get(m_type)  # type: ignore
         if old is not None:
             diff_str = diff_string(old, new)
         else:
             old, diff_str = "NC", "NC"
         new = f"{new:.3f}" if isinstance(new, float) else str(new)
         old = f"{old:.3f}" if isinstance(old, float) else str(old)
-        lines += (m_type.replace("_", " "), new, old, diff_str)
+        lines.extend((m_type.replace("_", " "), new, old, diff_str))
     return lines