From 58b9e6421b2246597c97c75640ee6337460cb0ba Mon Sep 17 00:00:00 2001
From: Claudiu Popa <pcmanticore@gmail.com>
Date: Mon, 16 Dec 2019 09:26:45 +0100
Subject: [PATCH] ``undefined-variable`` can now find undefined loop iterables

Close #498
---
 ChangeLog                                 |  4 ++++
 pylint/checkers/variables.py              | 10 +++++++++-
 tests/functional/u/undefined_variable.py  |  7 +++++++
 tests/functional/u/undefined_variable.txt |  1 +
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index f68cdb2260..997195510b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -29,6 +29,10 @@ Release date: TBA
 
    Close #3301
 
+* ``undefined-variable`` can now find undefined loop iterables
+
+   Close #498
+
 * ``safe_infer`` can infer a value as long as all the paths share the same type.
 
   Close #2503
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index 6a28870536..4449bd960e 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -546,7 +546,7 @@ def mark_as_consumed(self, name, new_node):
         del self.to_consume[name]
 
     def get_next_to_consume(self, node):
-        # mark the name as consumed if it's defined in this scope
+        # Get the definition of `node` from this scope
         name = node.name
         parent_node = node.parent
         found_node = self.to_consume.get(name)
@@ -558,6 +558,14 @@ def get_next_to_consume(self, node):
             lhs = found_node[0].parent.targets[0]
             if lhs.name == name:  # this name is defined in this very statement
                 found_node = None
+
+        if (
+            found_node
+            and isinstance(parent_node, astroid.For)
+            and parent_node.iter == node
+            and parent_node.target in found_node
+        ):
+            found_node = None
         return found_node
 
 
diff --git a/tests/functional/u/undefined_variable.py b/tests/functional/u/undefined_variable.py
index 4323bfd3c7..4787beb9a2 100644
--- a/tests/functional/u/undefined_variable.py
+++ b/tests/functional/u/undefined_variable.py
@@ -274,3 +274,10 @@ def func_should_fail(_dt: datetime):  # [used-before-assignment]
 def tick(counter: Counter, name: str, dictionary: OrderedDict) -> OrderedDict:
     counter[name] += 1
     return dictionary
+
+
+# pylint: disable=unused-argument
+def not_using_loop_variable_accordingly(iterator):
+    for iteree in iteree: # [undefined-variable]
+        yield iteree
+# pylint: enable=unused-argument
diff --git a/tests/functional/u/undefined_variable.txt b/tests/functional/u/undefined_variable.txt
index fa86ff5b6e..d9aa6c86db 100644
--- a/tests/functional/u/undefined_variable.txt
+++ b/tests/functional/u/undefined_variable.txt
@@ -25,3 +25,4 @@ undefined-variable:170::Undefined variable 'unicode_3'
 undefined-variable:225:LambdaClass4.<lambda>:Undefined variable 'LambdaClass4'
 undefined-variable:233:LambdaClass5.<lambda>:Undefined variable 'LambdaClass5'
 used-before-assignment:254:func_should_fail:Using variable 'datetime' before assignment
+undefined-variable:281:not_using_loop_variable_accordingly:Undefined variable 'iteree'