Make ``undefined-variable`` flag type annotation without value assignment (#5158)

Closes #5140

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index b4027d602..44044f76b 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -1186,6 +1186,8 @@ class VariablesChecker(BaseChecker):
                                 )
                         elif current_consumer.scope_type == "lambda":
                             self.add_message("undefined-variable", node=node, args=name)
+                elif self._is_only_type_assignment(node, name, defstmt):
+                    self.add_message("undefined-variable", node=node, args=name)
 
             current_consumer.mark_as_consumed(name, found_nodes)
             # check it's not a loop variable used outside the loop
@@ -1548,6 +1550,22 @@ class VariablesChecker(BaseChecker):
 
         return maybee0601, annotation_return, use_outer_definition
 
+    @staticmethod
+    def _is_only_type_assignment(
+        node: nodes.Name, name: str, defstmt: nodes.Statement
+    ) -> bool:
+        """Check if variable only gets assigned a type and never a value"""
+        if not isinstance(defstmt, nodes.AnnAssign) or defstmt.value:
+            return False
+        for ref_node in node.scope().locals[name][1:]:
+            if ref_node.lineno < node.lineno:
+                if not (
+                    isinstance(ref_node.parent, nodes.AnnAssign)
+                    and ref_node.parent.value
+                ):
+                    return False
+        return True
+
     def _ignore_class_scope(self, node):
         """
         Return True if the node is in a local class scope, as an assignment.