Fix cyclic import with TYPE_CHECKING (#4703)

* Fix cyclic-import with TYPE_CHECKING
* Use new astroid helper method

Author: cdce8p

ChangeLog

@@ -52,6 +52,10 @@ Release date: TBA
 
   Closes #4664
 
+* Don't emit ``cyclic-import`` message if import is guarded by ``typing.TYPE_CHECKING``.
+
+  Closes #3525
+
 * Clarify documentation for consider-using-from-import
 
 * Don't emit ``unreachable`` warning for empty generator functions

pylint/checkers/imports.py

@@ -813,7 +813,9 @@ def _get_imported_module(self, importnode, modname):
             self.add_message("import-error", args=repr(dotted_modname), node=importnode)
         return None
 
-    def _add_imported_module(self, node, importedmodname):
+    def _add_imported_module(
+        self, node: Union[astroid.Import, astroid.ImportFrom], importedmodname: str
+    ) -> None:
         """notify an imported module, used to analyze dependencies"""
         module_file = node.root().file
         context_name = node.root().name
@@ -826,6 +828,10 @@ def _add_imported_module(self, node, importedmodname):
         except ImportError:
             pass
 
+        in_type_checking_block = (
+            isinstance(node.parent, astroid.If) and node.parent.is_typing_guard()
+        )
+
         if context_name == importedmodname:
             self.add_message("import-self", node=node)
 
@@ -845,7 +851,10 @@ def _add_imported_module(self, node, importedmodname):
 
             # update import graph
             self.import_graph[context_name].add(importedmodname)
-            if not self.linter.is_message_enabled("cyclic-import", line=node.lineno):
+            if (
+                not self.linter.is_message_enabled("cyclic-import", line=node.lineno)
+                or in_type_checking_block
+            ):
                 self._excluded_edges[context_name].add(importedmodname)
 
     def _check_preferred_module(self, node, mod_path):

tests/input/func_noerror_cycle/__init__.py

@@ -0,0 +1,3 @@
+# https://github.com/PyCQA/pylint/issues/3525
+# `cyclic-import` should not be emitted if one import
+# is guarded by `typing.TYPE_CHECKING`

tests/input/func_noerror_cycle/a.py

@@ -0,0 +1,8 @@
+# pylint: disable=missing-docstring
+from typing import List
+
+from .b import var
+
+LstT = List[int]
+
+print(var)

tests/input/func_noerror_cycle/b.py

@@ -0,0 +1,7 @@
+# pylint: disable=missing-docstring
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from .a import LstT
+
+var: "LstT" = [1, 2]

tests/messages/func_noerror_cycle.txt

@@ -121,7 +121,7 @@ def gen_tests(filter_rgx):
         tests.append((module_file, messages_file, dependencies))
     if UPDATE_FILE.exists():
         return tests
-    assert len(tests) < 12, "Please do not add new test cases here." + "\n".join(
+    assert len(tests) < 13, "Please do not add new test cases here." + "\n".join(
         str(k) for k in tests if not k[2]
     )
     return tests