fix: unreachable code analysis inside for loops (vyperlang#3731)

unreachable code analysis did not analyze for loop bodies.
fix: in `find_terminating_node()`, recurse into the bodies of for loops.

tests/functional/syntax/test_unbalanced_return.py

@@ -118,6 +118,39 @@ def foo() -> uint256:
     """,
         StructureException,
     ),
+    (
+        """
+@internal
+def foo() -> uint256:
+    for i: uint256 in range(10):
+        if i == 11:
+            return 1
+        """,
+        FunctionDeclarationException,
+    ),
+    (
+        """
+@internal
+def foo() -> uint256:
+    for i: uint256 in range(9):
+        if i == 11:
+            return 1
+    if block.number % 2 == 0:
+        return 1
+        """,
+        FunctionDeclarationException,
+    ),
+    (
+        """
+@internal
+def foo() -> uint256:
+    for i: uint256 in range(10):
+        return 1
+        pass  # unreachable
+    return 5
+        """,
+        StructureException,
+    ),
 ]
 
 
@@ -187,6 +220,13 @@ def foo() -> int128:
     else:
         raw_revert(b"vyper")
     """,
+    """
+@external
+def foo() -> int128:
+    for i: uint256 in range(1):
+        return 1
+    return 0
+    """,
 ]
 
 

vyper/ast/nodes.pyi

@@ -257,6 +257,10 @@ class IfExp(ExprNode):
     body: ExprNode = ...
     orelse: ExprNode = ...
 
-class For(VyperNode): ...
+class For(VyperNode):
+    target: ExprNode
+    iter: ExprNode
+    body: list[VyperNode]
+
 class Break(VyperNode): ...
 class Continue(VyperNode): ...

vyper/semantics/analysis/local.py

@@ -74,6 +74,7 @@ def find_terminating_node(node_list: list) -> Optional[vy_ast.VyperNode]:
     for node in node_list:
         if ret is not None:
             raise StructureException("Unreachable code!", node)
+
         if node.is_terminus:
             ret = node
 
@@ -87,6 +88,10 @@ def find_terminating_node(node_list: list) -> Optional[vy_ast.VyperNode]:
             if body_terminates is not None and else_terminates is not None:
                 ret = else_terminates
 
+        if isinstance(node, vy_ast.For):
+            # call find_terminating_node for its side effects
+            find_terminating_node(node.body)
+
     return ret