fix: guard against iterating over empty list in for loop (#3197)

without this guard, the typechecker tries every possible type, which results in a bad error message
vyperlang · Jan 6, 2023 · 13ebcbe · 13ebcbe
1 parent a16af3d
commit 13ebcbe
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diff --git a/tests/parser/features/iteration/test_for_in_list.py b/tests/parser/features/iteration/test_for_in_list.py
@@ -658,6 +658,20 @@ def foo():
     for i in range(0):
         pass
     """,
+    """
+@external
+def foo():
+    for i in []:
+        pass
+    """,
+    """
+FOO: constant(DynArray[uint256, 3]) = []
+
+@external
+def foo():
+    for i in FOO:
+        pass
+    """,
     (
         """
 @external

diff --git a/vyper/semantics/analysis/local.py b/vyper/semantics/analysis/local.py
@@ -383,6 +383,9 @@ def visit_For(self, node):
 
         else:
             # iteration over a variable or literal list
+            if isinstance(node.iter, vy_ast.List) and len(node.iter.elements) == 0:
+                raise StructureException("For loop must have at least 1 iteration", node.iter)
+
             type_list = [
                 i.value_type
                 for i in get_possible_types_from_node(node.iter)