From ab7012c5386f8fc31cace97fb7c6d812e627ddfb Mon Sep 17 00:00:00 2001
From: LordBaryhobal <lordbaryhobal@gmail.com>
Date: Wed, 8 Jul 2026 19:21:19 +0200
Subject: [PATCH] fix(checker): leaking for-loop iterator target

---
 midas/checker/python.py                       |  10 +-
 midas/checker/resolver.py                     |   2 +-
 tests/cases/checker/10_variable_defined.py    |   5 +
 .../checker/10_variable_defined.py.ref.json   | 124 ++++++++++++++++++
 4 files changed, 138 insertions(+), 3 deletions(-)

diff --git a/midas/checker/python.py b/midas/checker/python.py
index 2ed55d1..ef8e688 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -601,6 +601,10 @@ class PythonTyper(
         pass
 
     def visit_for_stmt(self, stmt: p.ForStmt) -> None:
+        outer_env: Environment = self.env
+        inner_env: Environment = Environment(self.env)
+        self.env = inner_env
+
         item_type: Type = UnknownType()
         iterator_type: Type = self.type_of(stmt.iterator)
         if iterator_type != UnknownType():
@@ -614,8 +618,10 @@ class PythonTyper(
 
         self._assign(stmt.location, stmt.target, item_type)
         self.judge(stmt.target, item_type)
-        env: Environment = Environment(self.env)
-        body_returned: bool = self.process_block(stmt.body, env)
+        body_returned: bool = self.process_block(stmt.body, inner_env)
+
+        self.env = outer_env
+
         if body_returned:
             raise ReturnException()
 
diff --git a/midas/checker/resolver.py b/midas/checker/resolver.py
index 1cc77db..16756fb 100644
--- a/midas/checker/resolver.py
+++ b/midas/checker/resolver.py
@@ -180,9 +180,9 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         pass
 
     def visit_for_stmt(self, stmt: p.ForStmt) -> None:
+        self.begin_scope()
         self.resolve(stmt.iterator)
         self._visit_assign(stmt.target)
-        self.begin_scope()
         self.resolve(*stmt.body)
         self.end_scope()
 
diff --git a/tests/cases/checker/10_variable_defined.py b/tests/cases/checker/10_variable_defined.py
index 41fef83..47b8d56 100644
--- a/tests/cases/checker/10_variable_defined.py
+++ b/tests/cases/checker/10_variable_defined.py
@@ -38,3 +38,8 @@ def fact(n: int) -> int:
     if n <= 1:
         return 1
     return n * fact(n - 1)
+
+
+for i in [1, 2, 3]:
+    _ = i
+_ = i
diff --git a/tests/cases/checker/10_variable_defined.py.ref.json b/tests/cases/checker/10_variable_defined.py.ref.json
index 28af712..40428e2 100644
--- a/tests/cases/checker/10_variable_defined.py.ref.json
+++ b/tests/cases/checker/10_variable_defined.py.ref.json
@@ -83,6 +83,20 @@
         ]
       },
       "message": "Unknown variable"
+    },
+    {
+      "type": "Warning",
+      "location": {
+        "start": [
+          45,
+          4
+        ],
+        "end": [
+          45,
+          5
+        ]
+      },
+      "message": "Unknown variable"
     }
   ],
   "judgments": [
@@ -522,6 +536,116 @@
       "type": {
         "name": "int"
       }
+    },
+    {
+      "location": {
+        "from": "L43:10",
+        "to": "L43:11"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 1
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L43:13",
+        "to": "L43:14"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 2
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L43:16",
+        "to": "L43:17"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 3
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L43:9",
+        "to": "L43:18"
+      },
+      "expr": {
+        "_type": "ListExpr",
+        "items": [
+          {
+            "_type": "LiteralExpr",
+            "value": 1
+          },
+          {
+            "_type": "LiteralExpr",
+            "value": 2
+          },
+          {
+            "_type": "LiteralExpr",
+            "value": 3
+          }
+        ]
+      },
+      "type": {
+        "name": "list",
+        "args": [
+          {
+            "name": "int"
+          }
+        ],
+        "body": {
+          "name": "list"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L43:4",
+        "to": "L43:5"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "i"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L44:8",
+        "to": "L44:9"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "i"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L45:4",
+        "to": "L45:5"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "i"
+      },
+      "type": {}
     }
   ]
 }
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