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>

19 files changed, 154 insertions, 63 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
 
 
diff --git a/pylint/checkers/base.py b/pylint/checkers/base.py
index d839d921e..2f1579cd6 100644
--- a/pylint/checkers/base.py
+++ b/pylint/checkers/base.py
@@ -66,7 +66,7 @@ import collections
 import itertools
 import re
 import sys
-from typing import Any, Iterator, Optional, Pattern
+from typing import Any, Dict, Iterator, Optional, Pattern, Union
 
 import astroid
 from astroid import nodes
@@ -81,6 +81,7 @@ from pylint.checkers.utils import (
     is_property_setter,
 )
 from pylint.reporters.ureports import nodes as reporter_nodes
+from pylint.typing import CheckerStats
 
 
 class NamingStyle:
@@ -386,36 +387,42 @@ def _has_abstract_methods(node):
     return len(utils.unimplemented_abstract_methods(node)) > 0
 
 
-def report_by_type_stats(sect, stats, old_stats):
+def report_by_type_stats(
+    sect,
+    stats: CheckerStats,
+    old_stats: CheckerStats,
+):
     """make a report of
 
     * percentage of different types documented
     * percentage of different types with a bad name
     """
     # percentage of different types documented and/or with a bad name
-    nice_stats = {}
+    nice_stats: Dict[str, Dict[str, str]] = {}
     for node_type in ("module", "class", "method", "function"):
         try:
-            total = stats[node_type]
+            total: int = stats[node_type]  # type: ignore
         except KeyError as e:
             raise exceptions.EmptyReportError() from e
         nice_stats[node_type] = {}
         if total != 0:
             try:
-                documented = total - stats["undocumented_" + node_type]
+                undocumented_node: int = stats["undocumented_" + node_type]  # type: ignore
+                documented = total - undocumented_node
                 percent = (documented * 100.0) / total
                 nice_stats[node_type]["percent_documented"] = f"{percent:.2f}"
             except KeyError:
                 nice_stats[node_type]["percent_documented"] = "NC"
             try:
-                percent = (stats["badname_" + node_type] * 100.0) / total
+                badname_node: int = stats["badname_" + node_type]  # type: ignore
+                percent = (badname_node * 100.0) / total
                 nice_stats[node_type]["percent_badname"] = f"{percent:.2f}"
             except KeyError:
                 nice_stats[node_type]["percent_badname"] = "NC"
     lines = ["type", "number", "old number", "difference", "%documented", "%badname"]
     for node_type in ("module", "class", "method", "function"):
         new = stats[node_type]
-        old = old_stats.get(node_type, None)
+        old: Optional[Union[str, int]] = old_stats.get(node_type, None)  # type: ignore
         if old is not None:
             diff_str = lint_utils.diff_string(old, new)
         else:
@@ -1082,7 +1089,7 @@ class BasicChecker(_BasicChecker):
 
     def __init__(self, linter):
         _BasicChecker.__init__(self, linter)
-        self.stats = None
+        self.stats: CheckerStats = {}
         self._tryfinallys = None
 
     def open(self):
@@ -1159,13 +1166,13 @@ class BasicChecker(_BasicChecker):
 
     def visit_module(self, _: nodes.Module) -> None:
         """check module name, docstring and required arguments"""
-        self.stats["module"] += 1
+        self.stats["module"] += 1  # type: ignore
 
     def visit_classdef(self, _: nodes.ClassDef) -> None:
         """check module name, docstring and redefinition
         increment branch counter
         """
-        self.stats["class"] += 1
+        self.stats["class"] += 1  # type: ignore
 
     @utils.check_messages(
         "pointless-statement", "pointless-string-statement", "expression-not-assigned"
@@ -1304,7 +1311,7 @@ class BasicChecker(_BasicChecker):
         """check function name, docstring, arguments, redefinition,
         variable names, max locals
         """
-        self.stats["method" if node.is_method() else "function"] += 1
+        self.stats["method" if node.is_method() else "function"] += 1  # type: ignore
         self._check_dangerous_default(node)
 
     visit_asyncfunctiondef = visit_functiondef
@@ -2040,7 +2047,7 @@ class NameChecker(_BasicChecker):
         )
 
         self.add_message(warning, node=node, args=args, confidence=confidence)
-        self.stats["badname_" + node_type] += 1
+        self.stats["badname_" + node_type] += 1  # type: ignore
 
     def _name_allowed_by_regex(self, name: str) -> bool:
         return name in self.config.good_names or any(
diff --git a/pylint/checkers/base_checker.py b/pylint/checkers/base_checker.py
index 5dfd7ea78..791a3cb1e 100644
--- a/pylint/checkers/base_checker.py
+++ b/pylint/checkers/base_checker.py
@@ -24,6 +24,7 @@ from pylint.constants import _MSG_ORDER, WarningScope
 from pylint.exceptions import InvalidMessageError
 from pylint.interfaces import UNDEFINED, IRawChecker, ITokenChecker, implements
 from pylint.message.message_definition import MessageDefinition
+from pylint.typing import CheckerStats
 from pylint.utils import get_rst_section, get_rst_title
 
 
@@ -51,6 +52,7 @@ class BaseChecker(OptionsProviderMixIn):
             self.name = self.name.lower()
         OptionsProviderMixIn.__init__(self)
         self.linter = linter
+        self.stats: CheckerStats = {}
 
     def __gt__(self, other):
         """Permit to sort a list of Checker by name."""
diff --git a/pylint/checkers/design_analysis.py b/pylint/checkers/design_analysis.py
index 9777b568e..362d299de 100644
--- a/pylint/checkers/design_analysis.py
+++ b/pylint/checkers/design_analysis.py
@@ -35,6 +35,7 @@ from pylint import utils
 from pylint.checkers import BaseChecker
 from pylint.checkers.utils import check_messages
 from pylint.interfaces import IAstroidChecker
+from pylint.typing import CheckerStats
 
 MSGS = {  # pylint: disable=consider-using-namedtuple-or-dataclass
     "R0901": (
@@ -391,7 +392,7 @@ class MisdesignChecker(BaseChecker):
 
     def __init__(self, linter=None):
         BaseChecker.__init__(self, linter)
-        self.stats = None
+        self.stats: CheckerStats = {}
         self._returns = None
         self._branches = None
         self._stmts = None
diff --git a/pylint/checkers/imports.py b/pylint/checkers/imports.py
index 7e0cda26d..8b413253f 100644
--- a/pylint/checkers/imports.py
+++ b/pylint/checkers/imports.py
@@ -68,6 +68,7 @@ from pylint.graph import DotBackend, get_cycles
 from pylint.interfaces import IAstroidChecker
 from pylint.lint import PyLinter
 from pylint.reporters.ureports.nodes import Paragraph, VerbatimText, VNode
+from pylint.typing import CheckerStats
 from pylint.utils import IsortDriver, get_global_option
 
 
@@ -423,7 +424,7 @@ class ImportsChecker(DeprecatedMixin, BaseChecker):
         self, linter: PyLinter = None
     ):  # pylint: disable=super-init-not-called # See https://github.com/PyCQA/pylint/issues/4941
         BaseChecker.__init__(self, linter)
-        self.stats: Dict[Any, Any] = {}
+        self.stats: CheckerStats = {}
         self.import_graph: collections.defaultdict = collections.defaultdict(set)
         self._imports_stack: List[Tuple[Any, Any]] = []
         self._first_non_import_node = None
@@ -839,9 +840,8 @@ class ImportsChecker(DeprecatedMixin, BaseChecker):
                 self._module_pkg[context_name] = context_name.rsplit(".", 1)[0]
 
             # handle dependencies
-            importedmodnames = self.stats["dependencies"].setdefault(
-                importedmodname, set()
-            )
+            dependencies_stat: Dict[str, Union[Set]] = self.stats["dependencies"]  # type: ignore
+            importedmodnames = dependencies_stat.setdefault(importedmodname, set())
             if context_name not in importedmodnames:
                 importedmodnames.add(context_name)
 
diff --git a/pylint/checkers/raw_metrics.py b/pylint/checkers/raw_metrics.py
index 028c68e7a..cc3f2729d 100644
--- a/pylint/checkers/raw_metrics.py
+++ b/pylint/checkers/raw_metrics.py
@@ -15,27 +15,32 @@
 # For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
 
 import tokenize
-from typing import Any
+from typing import Any, Optional, Union
 
 from pylint.checkers import BaseTokenChecker
 from pylint.exceptions import EmptyReportError
 from pylint.interfaces import ITokenChecker
 from pylint.reporters.ureports.nodes import Table
+from pylint.typing import CheckerStats
 from pylint.utils import diff_string
 
 
-def report_raw_stats(sect, stats, old_stats):
+def report_raw_stats(
+    sect,
+    stats: CheckerStats,
+    old_stats: CheckerStats,
+):
     """calculate percentage of code / doc / comment / empty"""
-    total_lines = stats["total_lines"]
+    total_lines: int = stats["total_lines"]  # type: ignore
     if not total_lines:
         raise EmptyReportError()
     sect.description = f"{total_lines} lines have been analyzed"
     lines = ["type", "number", "%", "previous", "difference"]
     for node_type in ("code", "docstring", "comment", "empty"):
         key = node_type + "_lines"
-        total = stats[key]
+        total: int = stats[key]  # type: ignore
         percent = float(total * 100) / total_lines
-        old = old_stats.get(key, None)
+        old: Optional[Union[int, str]] = old_stats.get(key, None)  # type: ignore
         if old is not None:
             diff_str = diff_string(old, total)
         else:
@@ -66,7 +71,7 @@ class RawMetricsChecker(BaseTokenChecker):
 
     def __init__(self, linter):
         BaseTokenChecker.__init__(self, linter)
-        self.stats = None
+        self.stats: CheckerStats = {}
 
     def open(self):
         """init statistics"""
diff --git a/pylint/checkers/similar.py b/pylint/checkers/similar.py
index 4ceb5d660..2a28e7d6c 100644
--- a/pylint/checkers/similar.py
+++ b/pylint/checkers/similar.py
@@ -73,6 +73,7 @@ from astroid import nodes
 from pylint.checkers import BaseChecker, MapReduceMixin, table_lines_from_stats
 from pylint.interfaces import IRawChecker
 from pylint.reporters.ureports.nodes import Table
+from pylint.typing import CheckerStats
 from pylint.utils import decoding_stream
 
 DEFAULT_MIN_SIMILARITY_LINE = 4
@@ -721,7 +722,11 @@ MSGS = {
 }
 
 
-def report_similarities(sect, stats, old_stats):
+def report_similarities(
+    sect,
+    stats: CheckerStats,
+    old_stats: CheckerStats,
+):
     """make a layout with some stats about duplication"""
     lines = ["", "now", "previous", "difference"]
     lines += table_lines_from_stats(
@@ -804,7 +809,7 @@ class SimilarChecker(BaseChecker, Similar, MapReduceMixin):
             ignore_imports=self.config.ignore_imports,
             ignore_signatures=self.config.ignore_signatures,
         )
-        self.stats = None
+        self.stats: CheckerStats = {}
 
     def set_option(self, optname, value, action=None, optdict=None):
         """method called to set an option (registered in the options list)
diff --git a/pylint/lint/parallel.py b/pylint/lint/parallel.py
index ad6830721..2f3d0dd05 100644
--- a/pylint/lint/parallel.py
+++ b/pylint/lint/parallel.py
@@ -3,10 +3,15 @@
 
 import collections
 import functools
+from typing import TYPE_CHECKING, Dict, List, Union
 
 from pylint import reporters
 from pylint.lint.utils import _patch_sys_path
 from pylint.message import Message
+from pylint.typing import CheckerStats
+
+if TYPE_CHECKING:
+    from typing import Counter  # typing.Counter added in Python 3.6.1
 
 try:
     import multiprocessing
@@ -30,20 +35,20 @@ def _get_new_args(message):
     return (message.msg_id, message.symbol, location, message.msg, message.confidence)
 
 
-def _merge_stats(stats):
-    merged = {}
-    by_msg = collections.Counter()
+def _merge_stats(stats: List[CheckerStats]):
+    merged: CheckerStats = {}
+    by_msg: "Counter[str]" = collections.Counter()
     for stat in stats:
-        message_stats = stat.pop("by_msg", {})
+        message_stats: Union["Counter[str]", Dict] = stat.pop("by_msg", {})  # type: ignore
         by_msg.update(message_stats)
 
         for key, item in stat.items():
             if key not in merged:
                 merged[key] = item
             elif isinstance(item, dict):
-                merged[key].update(item)
+                merged[key].update(item)  # type: ignore
             else:
-                merged[key] = merged[key] + item
+                merged[key] = merged[key] + item  # type: ignore
 
     merged["by_msg"] = by_msg
     return merged
diff --git a/pylint/lint/pylinter.py b/pylint/lint/pylinter.py
index 54614ad89..d731e71b3 100644
--- a/pylint/lint/pylinter.py
+++ b/pylint/lint/pylinter.py
@@ -31,6 +31,7 @@ from pylint.lint.utils import (
 )
 from pylint.message import MessageDefinitionStore, MessagesHandlerMixIn
 from pylint.reporters.ureports import nodes as report_nodes
+from pylint.typing import CheckerStats
 from pylint.utils import ASTWalker, FileState, utils
 from pylint.utils.pragma_parser import (
     OPTION_PO,
@@ -502,7 +503,7 @@ class PyLinter(
         self.file_state = FileState()
         self.current_name = None
         self.current_file = None
-        self.stats = None
+        self.stats: CheckerStats = {}
         self.fail_on_symbols = []
         # init options
         self._external_opts = options
@@ -729,8 +730,10 @@ class PyLinter(
                         self.fail_on_symbols.append(msg.symbol)
 
     def any_fail_on_issues(self):
-        return self.stats is not None and any(
-            x in self.fail_on_symbols for x in self.stats["by_msg"]
+        return (
+            self.stats
+            and self.stats.get("by_msg") is not None
+            and any(x in self.fail_on_symbols for x in self.stats["by_msg"])
         )
 
     def disable_noerror_messages(self):
diff --git a/pylint/lint/report_functions.py b/pylint/lint/report_functions.py
index 21cb3b824..12c4b0335 100644
--- a/pylint/lint/report_functions.py
+++ b/pylint/lint/report_functions.py
@@ -2,12 +2,18 @@
 # For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
 
 import collections
+from typing import DefaultDict, Dict, List, Tuple, Union
 
 from pylint import checkers, exceptions
 from pylint.reporters.ureports import nodes as report_nodes
+from pylint.typing import CheckerStats
 
 
-def report_total_messages_stats(sect, stats, previous_stats):
+def report_total_messages_stats(
+    sect,
+    stats: CheckerStats,
+    previous_stats: CheckerStats,
+):
     """make total errors / warnings report"""
     lines = ["type", "number", "previous", "difference"]
     lines += checkers.table_lines_from_stats(
@@ -16,14 +22,19 @@ def report_total_messages_stats(sect, stats, previous_stats):
     sect.append(report_nodes.Table(children=lines, cols=4, rheaders=1))
 
 
-def report_messages_stats(sect, stats, _):
+def report_messages_stats(
+    sect,
+    stats: CheckerStats,
+    _: CheckerStats,
+):
     """make messages type report"""
     if not stats["by_msg"]:
         # don't print this report when we didn't detected any errors
         raise exceptions.EmptyReportError()
-    in_order = sorted(
+    by_msg_stats: Dict[str, int] = stats["by_msg"]  # type: ignore
+    in_order: List[Tuple[int, str]] = sorted(
         (value, msg_id)
-        for msg_id, value in stats["by_msg"].items()
+        for msg_id, value in by_msg_stats.items()
         if not msg_id.startswith("I")
     )
     in_order.reverse()
@@ -33,16 +44,23 @@ def report_messages_stats(sect, stats, _):
     sect.append(report_nodes.Table(children=lines, cols=2, rheaders=1))
 
 
-def report_messages_by_module_stats(sect, stats, _):
+def report_messages_by_module_stats(
+    sect,
+    stats: CheckerStats,
+    _: CheckerStats,
+):
     """make errors / warnings by modules report"""
-    if len(stats["by_module"]) == 1:
+    module_stats: Dict[str, Dict[str, int]] = stats["by_module"]  # type: ignore
+    if len(module_stats) == 1:
         # don't print this report when we are analysing a single module
         raise exceptions.EmptyReportError()
-    by_mod = collections.defaultdict(dict)
+    by_mod: DefaultDict[str, Dict[str, Union[int, float]]] = collections.defaultdict(
+        dict
+    )
     for m_type in ("fatal", "error", "warning", "refactor", "convention"):
-        total = stats[m_type]
-        for module in stats["by_module"].keys():
-            mod_total = stats["by_module"][module][m_type]
+        total: int = stats[m_type]  # type: ignore
+        for module in module_stats.keys():
+            mod_total = module_stats[module][m_type]
             percent = 0 if total == 0 else float((mod_total) * 100) / total
             by_mod[module][m_type] = percent
     sorted_result = []
diff --git a/pylint/reporters/base_reporter.py b/pylint/reporters/base_reporter.py
index fda99f4ef..4cf5d5895 100644
--- a/pylint/reporters/base_reporter.py
+++ b/pylint/reporters/base_reporter.py
@@ -6,6 +6,7 @@ import sys
 from typing import List
 
 from pylint.message import Message
+from pylint.typing import CheckerStats
 
 
 class BaseReporter:
@@ -41,7 +42,7 @@ class BaseReporter:
     def display_reports(self, layout):
         """display results encapsulated in the layout tree"""
         self.section = 0
-        if hasattr(layout, "report_id"):
+        if layout.report_id:
             layout.children[0].children[0].data += f" ({layout.report_id})"
         self._display(layout)
 
@@ -65,5 +66,9 @@ class BaseReporter:
     def on_set_current_module(self, module, filepath):
         """Hook called when a module starts to be analysed."""
 
-    def on_close(self, stats, previous_stats):
+    def on_close(
+        self,
+        stats: CheckerStats,
+        previous_stats: CheckerStats,
+    ) -> None:
         """Hook called when a module finished analyzing."""
diff --git a/pylint/reporters/multi_reporter.py b/pylint/reporters/multi_reporter.py
index a4dbae53b..245c10f79 100644
--- a/pylint/reporters/multi_reporter.py
+++ b/pylint/reporters/multi_reporter.py
@@ -3,12 +3,13 @@
 
 
 import os
-from typing import IO, Any, AnyStr, Callable, List, Mapping, Optional, Union
+from typing import IO, Any, AnyStr, Callable, List, Optional, Union
 
 from pylint.interfaces import IReporter
 from pylint.message import Message
 from pylint.reporters.base_reporter import BaseReporter
 from pylint.reporters.ureports.nodes import BaseLayout
+from pylint.typing import CheckerStats
 
 AnyFile = IO[AnyStr]
 AnyPath = Union[str, bytes, os.PathLike]
@@ -95,8 +96,8 @@ class MultiReporter:
 
     def on_close(
         self,
-        stats: Mapping[Any, Any],
-        previous_stats: Mapping[Any, Any],
+        stats: CheckerStats,
+        previous_stats: CheckerStats,
     ) -> None:
         """hook called when a module finished analyzing"""
         for rep in self._sub_reporters:
diff --git a/pylint/reporters/reports_handler_mix_in.py b/pylint/reporters/reports_handler_mix_in.py
index 914556ef4..450d383f5 100644
--- a/pylint/reporters/reports_handler_mix_in.py
+++ b/pylint/reporters/reports_handler_mix_in.py
@@ -2,9 +2,14 @@
 # For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
 
 import collections
+from typing import TYPE_CHECKING, Any
 
 from pylint.exceptions import EmptyReportError
 from pylint.reporters.ureports.nodes import Section
+from pylint.typing import CheckerStats
+
+if TYPE_CHECKING:
+    from pylint.lint.pylinter import PyLinter
 
 
 class ReportsHandlerMixIn:
@@ -49,7 +54,11 @@ class ReportsHandlerMixIn:
         """
         return self._reports_state.get(reportid, True)
 
-    def make_reports(self, stats, old_stats):
+    def make_reports(  # type: ignore # ReportsHandlerMixIn is always mixed with PyLinter
+        self: "PyLinter",
+        stats: CheckerStats,
+        old_stats: CheckerStats,
+    ):
         """render registered reports"""
         sect = Section("Report", f"{self.stats['statement']} statements analysed.")
         for checker in self.report_order():
@@ -65,7 +74,9 @@ class ReportsHandlerMixIn:
                 sect.append(report_sect)
         return sect
 
-    def add_stats(self, **kwargs):
+    def add_stats(  # type: ignore # ReportsHandlerMixIn is always mixed with PyLinter
+        self: "PyLinter", **kwargs: Any
+    ) -> CheckerStats:
         """add some stats entries to the statistic dictionary
         raise an AssertionError if there is a key conflict
         """
diff --git a/pylint/reporters/ureports/nodes.py b/pylint/reporters/ureports/nodes.py
index 3f7842a18..c5c14737d 100644
--- a/pylint/reporters/ureports/nodes.py
+++ b/pylint/reporters/ureports/nodes.py
@@ -14,6 +14,7 @@
 
 A micro report is a tree of layout and content objects.
 """
+from typing import Optional
 
 
 class VNode:
@@ -126,6 +127,7 @@ class Section(BaseLayout):
             self.insert(0, Paragraph([Text(description)]))
         if title:
             self.insert(0, Title(children=(title,)))
+        self.report_id: Optional[str] = None
 
 
 class EvaluationSection(Section):
diff --git a/pylint/testutils/unittest_linter.py b/pylint/testutils/unittest_linter.py
index 2d0a4f2c3..b75592ce6 100644
--- a/pylint/testutils/unittest_linter.py
+++ b/pylint/testutils/unittest_linter.py
@@ -3,6 +3,7 @@
 
 from pylint.testutils.global_test_linter import linter
 from pylint.testutils.output_line import Message
+from pylint.typing import CheckerStats
 
 
 class UnittestLinter:
@@ -12,7 +13,7 @@ class UnittestLinter:
 
     def __init__(self):
         self._messages = []
-        self.stats = {}
+        self.stats: CheckerStats = {}
 
     def release_messages(self):
         try:
diff --git a/pylint/typing.py b/pylint/typing.py
new file mode 100644
index 000000000..9ce1c587f
--- /dev/null
+++ b/pylint/typing.py
@@ -0,0 +1,14 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
+
+"""A collection of typing utilities."""
+from typing import TYPE_CHECKING, Dict, List, Union
+
+if TYPE_CHECKING:
+    from typing import Counter  # typing.Counter added in Python 3.6.1
+
+
+# The base type of the "stats" attribute of a checker
+CheckerStats = Dict[
+    str, Union[int, "Counter[str]", List, Dict[str, Union[int, str, Dict[str, int]]]]
+]
diff --git a/tests/lint/unittest_lint.py b/tests/lint/unittest_lint.py
index 18656ad74..c31cbdba0 100644
--- a/tests/lint/unittest_lint.py
+++ b/tests/lint/unittest_lint.py
@@ -48,7 +48,7 @@ from io import StringIO
 from os import chdir, getcwd
 from os.path import abspath, basename, dirname, isdir, join, sep
 from shutil import rmtree
-from typing import Iterable, Iterator, List, Optional, Tuple
+from typing import Dict, Iterable, Iterator, List, Optional, Tuple
 
 import platformdirs
 import pytest
@@ -828,7 +828,8 @@ def test_by_module_statement_value(init_linter: PyLinter) -> None:
     linter = init_linter
     linter.check(os.path.join(os.path.dirname(__file__), "data"))
 
-    for module, module_stats in linter.stats["by_module"].items():
+    by_module_stats: Dict[str, Dict[str, int]] = linter.stats["by_module"]  # type: ignore
+    for module, module_stats in by_module_stats.items():
 
         linter2 = init_linter
         if module == "data":
diff --git a/tests/test_check_parallel.py b/tests/test_check_parallel.py
index 102c0f122..66236ac8d 100644
--- a/tests/test_check_parallel.py
+++ b/tests/test_check_parallel.py
@@ -24,6 +24,7 @@ from pylint.lint.parallel import _worker_check_single_file as worker_check_singl
 from pylint.lint.parallel import _worker_initialize as worker_initialize
 from pylint.lint.parallel import check_parallel
 from pylint.testutils import GenericTestReporter as Reporter
+from pylint.typing import CheckerStats
 
 
 def _gen_file_data(idx: int = 0) -> Tuple[str, str, str]:
@@ -101,7 +102,7 @@ class ParallelTestChecker(BaseChecker):
         super().__init__(linter)
         self.data: List[str] = []
         self.linter = linter
-        self.stats = None
+        self.stats: CheckerStats = {}
 
     def open(self) -> None:
         """init the checkers: reset statistics information"""
diff --git a/tests/test_regr.py b/tests/test_regr.py
index 793a19612..12dd03406 100644
--- a/tests/test_regr.py
+++ b/tests/test_regr.py
@@ -23,7 +23,7 @@ to be incorporated in the automatic functional test framework
 import os
 import sys
 from os.path import abspath, dirname, join
-from typing import Iterator
+from typing import Dict, Iterator
 
 import astroid
 import pytest
@@ -111,12 +111,14 @@ def modify_path() -> Iterator:
 def test_check_package___init__(finalize_linter: PyLinter) -> None:
     filename = "package.__init__"
     finalize_linter.check(filename)
-    checked = list(finalize_linter.stats["by_module"].keys())
+    by_module_stats: Dict[str, Dict[str, int]] = finalize_linter.stats["by_module"]  # type: ignore
+    checked = list(by_module_stats.keys())
     assert checked == [filename]
 
     os.chdir(join(REGR_DATA, "package"))
     finalize_linter.check("__init__")
-    checked = list(finalize_linter.stats["by_module"].keys())
+    by_module_stats: Dict[str, Dict[str, int]] = finalize_linter.stats["by_module"]  # type: ignore
+    checked = list(by_module_stats.keys())
     assert checked == ["__init__"]