Detect unreachable code after sys.exit, quit, exit, and os._exit (#7520)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Co-authored-by: Mark Byrne <31762852+mbyrnepr2@users.noreply.github.com>

doc/whatsnew/fragments/519.false_negative

@@ -0,0 +1,3 @@
+Code following a call to  ``quit``,  ``exit``, ``sys.exit`` or ``os._exit`` will be marked as `unreachable`.
+
+Refs #519

pylint/checkers/base/basic_checker.py

@@ -17,7 +17,7 @@
 
 from pylint import utils as lint_utils
 from pylint.checkers import BaseChecker, utils
-from pylint.interfaces import HIGH, INFERENCE
+from pylint.interfaces import HIGH, INFERENCE, Confidence
 from pylint.reporters.ureports import nodes as reporter_nodes
 from pylint.utils import LinterStats
 
@@ -657,13 +657,38 @@ def _check_misplaced_format_function(self, call_node: nodes.Call) -> None:
             ):
                 self.add_message("misplaced-format-function", node=call_node)
 
+    @staticmethod
+    def _is_terminating_func(node: nodes.Call) -> bool:
+        """Detect call to exit(), quit(), os._exit(), or sys.exit()."""
+        if (
+            not isinstance(node.func, nodes.Attribute)
+            and not (isinstance(node.func, nodes.Name))
+            or isinstance(node.parent, nodes.Lambda)
+        ):
+            return False
+
+        qnames = {"_sitebuiltins.Quitter", "sys.exit", "posix._exit", "nt._exit"}
+
+        try:
+            for inferred in node.func.infer():
+                if hasattr(inferred, "qname") and inferred.qname() in qnames:
+                    return True
+        except (StopIteration, astroid.InferenceError):
+            pass
+
+        return False
+
     @utils.only_required_for_messages(
-        "eval-used", "exec-used", "bad-reversed-sequence", "misplaced-format-function"
+        "eval-used",
+        "exec-used",
+        "bad-reversed-sequence",
+        "misplaced-format-function",
+        "unreachable",
     )
     def visit_call(self, node: nodes.Call) -> None:
-        """Visit a Call node -> check if this is not a disallowed builtin
-        call and check for * or ** use.
-        """
+        """Visit a Call node."""
+        if self._is_terminating_func(node):
+            self._check_unreachable(node, confidence=INFERENCE)
         self._check_misplaced_format_function(node)
         if isinstance(node.func, nodes.Name):
             name = node.func.name
@@ -731,7 +756,9 @@ def leave_tryfinally(self, _: nodes.TryFinally) -> None:
         self._tryfinallys.pop()
 
     def _check_unreachable(
-        self, node: nodes.Return | nodes.Continue | nodes.Break | nodes.Raise
+        self,
+        node: nodes.Return | nodes.Continue | nodes.Break | nodes.Raise | nodes.Call,
+        confidence: Confidence = HIGH,
     ) -> None:
         """Check unreachable code."""
         unreachable_statement = node.next_sibling()
@@ -746,7 +773,9 @@ def _check_unreachable(
                 unreachable_statement = unreachable_statement.next_sibling()
                 if unreachable_statement is None:
                     return
-            self.add_message("unreachable", node=unreachable_statement, confidence=HIGH)
+            self.add_message(
+                "unreachable", node=unreachable_statement, confidence=confidence
+            )
 
     def _check_not_in_finally(
         self,

tests/functional/u/unreachable.py

@@ -1,5 +1,9 @@
-# pylint: disable=missing-docstring, broad-exception-raised
+# pylint: disable=missing-docstring, broad-exception-raised, too-few-public-methods, redefined-outer-name
+# pylint: disable=consider-using-sys-exit, protected-access
 
+import os
+import signal
+import sys
 
 def func1():
     return 1
@@ -32,3 +36,46 @@ def func6():
     return
     yield
     print("unreachable")  # [unreachable]
+
+def func7():
+    sys.exit(1)
+    var = 2 + 2  # [unreachable]
+    print(var)
+
+def func8():
+    signal.signal(signal.SIGTERM, lambda *args: sys.exit(0))
+    try:
+        print(1)
+    except KeyboardInterrupt:
+        pass
+
+class FalseExit:
+    def exit(self, number):
+        print(f"False positive this is not sys.exit({number})")
+
+def func_false_exit():
+    sys  = FalseExit()
+    sys.exit(1)
+    var = 2 + 2
+    print(var)
+
+def func9():
+    os._exit()
+    var = 2 + 2  # [unreachable]
+    print(var)
+
+def func10():
+    exit()
+    var = 2 + 2  # [unreachable]
+    print(var)
+
+def func11():
+    quit()
+    var = 2 + 2  # [unreachable]
+    print(var)
+
+incognito_function = sys.exit
+def func12():
+    incognito_function()
+    var = 2 + 2  # [unreachable]
+    print(var)

tests/functional/u/unreachable.txt

@@ -1,5 +1,10 @@
-unreachable:6:4:6:24:func1:Unreachable code:HIGH
-unreachable:11:8:11:28:func2:Unreachable code:HIGH
-unreachable:17:8:17:28:func3:Unreachable code:HIGH
-unreachable:21:4:21:16:func4:Unreachable code:HIGH
-unreachable:34:4:34:24:func6:Unreachable code:HIGH
+unreachable:10:4:10:24:func1:Unreachable code:HIGH
+unreachable:15:8:15:28:func2:Unreachable code:HIGH
+unreachable:21:8:21:28:func3:Unreachable code:HIGH
+unreachable:25:4:25:16:func4:Unreachable code:HIGH
+unreachable:38:4:38:24:func6:Unreachable code:HIGH
+unreachable:42:4:42:15:func7:Unreachable code:INFERENCE
+unreachable:64:4:64:15:func9:Unreachable code:INFERENCE
+unreachable:69:4:69:15:func10:Unreachable code:INFERENCE
+unreachable:74:4:74:15:func11:Unreachable code:INFERENCE
+unreachable:80:4:80:15:func12:Unreachable code:INFERENCE