Add new check: import-used-only-for-typechecking

pylint/checkers/variables.py

@@ -28,6 +28,7 @@
 from pylint.checkers.utils import (
     in_type_checking_block,
     is_module_ignored,
+    is_node_in_type_annotation_context,
     is_postponed_evaluation_enabled,
     is_sys_guard,
     overridden_method,
@@ -459,6 +460,11 @@ def _has_locals_call_after_node(stmt: nodes.NodeNG, scope: nodes.FunctionDef) ->
         "Used when an imported module or variable is not used from a "
         "`'from X import *'` style import.",
     ),
+    "W0615": (
+        "`%s` used only for typechecking but imported outside of a typechecking block",
+        "import-used-only-for-typechecking",
+        "Used when an import is used only for typechecking but imported outside of a typechecking block.",
+    ),
     "W0621": (
         "Redefining name %r from outer scope (line %s)",
         "redefined-outer-name",
@@ -529,6 +535,7 @@ class ScopeConsumer(NamedTuple):
 
     to_consume: dict[str, list[nodes.NodeNG]]
     consumed: dict[str, list[nodes.NodeNG]]
+    consumed_as_type: dict[str, list[nodes.NodeNG]]
     consumed_uncertain: defaultdict[str, list[nodes.NodeNG]]
     scope_type: str
 
@@ -538,7 +545,11 @@ class NamesConsumer:
 
     def __init__(self, node: nodes.NodeNG, scope_type: str) -> None:
         self._atomic = ScopeConsumer(
-            copy.copy(node.locals), {}, collections.defaultdict(list), scope_type
+            copy.copy(node.locals),
+            {},
+            {},
+            collections.defaultdict(list),
+            scope_type,
         )
         self.node = node
         self.names_under_always_false_test: set[str] = set()
@@ -547,15 +558,20 @@ def __init__(self, node: nodes.NodeNG, scope_type: str) -> None:
     def __repr__(self) -> str:
         _to_consumes = [f"{k}->{v}" for k, v in self._atomic.to_consume.items()]
         _consumed = [f"{k}->{v}" for k, v in self._atomic.consumed.items()]
+        _consumed_as_type = [
+            f"{k}->{v}" for k, v in self._atomic.consumed_as_type.items()
+        ]
         _consumed_uncertain = [
             f"{k}->{v}" for k, v in self._atomic.consumed_uncertain.items()
         ]
         to_consumes = ", ".join(_to_consumes)
         consumed = ", ".join(_consumed)
+        consumed_as_type = ", ".join(_consumed_as_type)
         consumed_uncertain = ", ".join(_consumed_uncertain)
         return f"""
 to_consume : {to_consumes}
 consumed : {consumed}
+consumed_as_type : {consumed_as_type}
 consumed_uncertain: {consumed_uncertain}
 scope_type : {self._atomic.scope_type}
 """
@@ -571,6 +587,10 @@ def to_consume(self) -> dict[str, list[nodes.NodeNG]]:
     def consumed(self) -> dict[str, list[nodes.NodeNG]]:
         return self._atomic.consumed
 
+    @property
+    def consumed_as_type(self) -> dict[str, list[nodes.NodeNG]]:
+        return self._atomic.consumed_as_type
+
     @property
     def consumed_uncertain(self) -> defaultdict[str, list[nodes.NodeNG]]:
         """Retrieves nodes filtered out by get_next_to_consume() that may not
@@ -587,19 +607,32 @@ def consumed_uncertain(self) -> defaultdict[str, list[nodes.NodeNG]]:
     def scope_type(self) -> str:
         return self._atomic.scope_type
 
-    def mark_as_consumed(self, name: str, consumed_nodes: list[nodes.NodeNG]) -> None:
+    def mark_as_consumed(
+        self,
+        name: str,
+        consumed_nodes: list[nodes.NodeNG],
+        consumed_as_type: bool = False,
+    ) -> None:
         """Mark the given nodes as consumed for the name.
 
         If all of the nodes for the name were consumed, delete the name from
         the to_consume dictionary
         """
-        unconsumed = [n for n in self.to_consume[name] if n not in set(consumed_nodes)]
-        self.consumed[name] = consumed_nodes
+        consumed = self.consumed_as_type if consumed_as_type else self.consumed
+        consumed[name] = consumed_nodes
 
-        if unconsumed:
-            self.to_consume[name] = unconsumed
-        else:
-            del self.to_consume[name]
+        if name in self.to_consume:
+            unconsumed = [
+                n for n in self.to_consume[name] if n not in set(consumed_nodes)
+            ]
+
+            if unconsumed:
+                self.to_consume[name] = unconsumed
+            else:
+                del self.to_consume[name]
+
+        if not consumed_as_type and name in self.consumed_as_type:
+            del self.consumed_as_type[name]
 
     def get_next_to_consume(self, node: nodes.Name) -> list[nodes.NodeNG] | None:
         """Return a list of the nodes that define `node` from this scope.
@@ -642,6 +675,9 @@ def get_next_to_consume(self, node: nodes.Name) -> list[nodes.NodeNG] | None:
         if VariablesChecker._comprehension_between_frame_and_node(node):
             return found_nodes
 
+        if found_nodes is None:
+            found_nodes = self.consumed_as_type.get(name)
+
         # Filter out assignments in ExceptHandlers that node is not contained in
         if found_nodes:
             found_nodes = [
@@ -1415,7 +1451,8 @@ def leave_module(self, node: nodes.Module) -> None:
         assert len(self._to_consume) == 1
 
         self._check_metaclasses(node)
-        not_consumed = self._to_consume.pop().to_consume
+        consumer = self._to_consume.pop()
+        not_consumed = consumer.to_consume
         # attempt to check for __all__ if defined
         if "__all__" in node.locals:
             self._check_all(node, not_consumed)
@@ -1427,7 +1464,7 @@ def leave_module(self, node: nodes.Module) -> None:
         if not self.linter.config.init_import and node.package:
             return
 
-        self._check_imports(not_consumed)
+        self._check_imports(not_consumed, consumer.consumed_as_type)
         self._type_annotation_names = []
 
     def visit_classdef(self, node: nodes.ClassDef) -> None:
@@ -1729,7 +1766,11 @@ def _undefined_and_used_before_checker(
                 # They will have already had a chance to emit used-before-assignment.
                 # We check here instead of before every single return in _check_consumer()
                 nodes_to_consume += current_consumer.consumed_uncertain[node.name]
-                current_consumer.mark_as_consumed(node.name, nodes_to_consume)
+                current_consumer.mark_as_consumed(
+                    node.name,
+                    nodes_to_consume,
+                    consumed_as_type=is_node_in_type_annotation_context(node),
+                )
             if action is VariableVisitConsumerAction.CONTINUE:
                 continue
             if action is VariableVisitConsumerAction.RETURN:
@@ -3195,7 +3236,11 @@ def _check_globals(self, not_consumed: dict[str, nodes.NodeNG]) -> None:
                 self.add_message("unused-variable", args=(name,), node=node)
 
     # pylint: disable = too-many-branches
-    def _check_imports(self, not_consumed: dict[str, list[nodes.NodeNG]]) -> None:
+    def _check_imports(
+        self,
+        not_consumed: dict[str, list[nodes.NodeNG]],
+        consumed_as_type: dict[str, list[nodes.NodeNG]],
+    ) -> None:
         local_names = _fix_dot_imports(not_consumed)
         checked = set()
         unused_wildcard_imports: defaultdict[
@@ -3282,8 +3327,26 @@ def _check_imports(self, not_consumed: dict[str, list[nodes.NodeNG]]) -> None:
             self.add_message(
                 "unused-wildcard-import", args=(arg_string, module[0]), node=module[1]
             )
+
+        self._check_type_imports(consumed_as_type)
+
         del self._to_consume
 
+    def _check_type_imports(
+        self,
+        consumed_as_type: dict[str, list[nodes.NodeNG]],
+    ) -> None:
+        for name, import_node in _fix_dot_imports(consumed_as_type):
+            if import_node.names[0][0] == "*":
+                continue
+
+            if not in_type_checking_block(import_node):
+                self.add_message(
+                    "import-used-only-for-typechecking",
+                    args=name,
+                    node=import_node,
+                )
+
     def _check_metaclasses(self, node: nodes.Module | nodes.FunctionDef) -> None:
         """Update consumption analysis for metaclasses."""
         consumed: list[tuple[dict[str, list[nodes.NodeNG]], str]] = []
@@ -3325,7 +3388,7 @@ def _check_classdef_metaclasses(
         name = METACLASS_NAME_TRANSFORMS.get(name, name)
         if name:
             # check enclosing scopes starting from most local
-            for scope_locals, _, _, _ in self._to_consume[::-1]:
+            for scope_locals, _, _, _, _ in self._to_consume[::-1]:
                 found_nodes = scope_locals.get(name, [])
                 for found_node in found_nodes:
                     if found_node.lineno <= klass.lineno: