From 4eebf8bd04fc29b944d77a758daa0b88f1e86efd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C4=B0lker=20O=C4=9Fulcan=20Say=C4=B1n?=
 <47698920+iosayin@users.noreply.github.com>
Date: Wed, 14 Oct 2026 13:46:16 +0300
Subject: [PATCH] fix(graphs): use None sentinel in Boruvka MST and un-ignore
 ty not-iterable

`Graph.boruvka_mst` stored `-1` in `cheap_edge` as a "no edge yet"
marker next to `[head, tail, weight]` lists. Mixing an int sentinel with
list values makes the later unpacking `head, tail, weight = ...` fail
type checking (`int & ~Literal[-1]` is not iterable), which was the only
`not-iterable` diagnostic left in the repository.

Use `None` as the sentinel with an explicit `list[int] | None` value type
and narrow through a local variable. Behaviour is unchanged.

With that diagnostic gone, remove `rules.not-iterable = "ignore"` from
`[tool.ty]` in pyproject.toml.

Part of #15187
---
 graphs/minimum_spanning_tree_boruvka.py | 17 ++++++++---------
 pyproject.toml                          |  1 -
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/graphs/minimum_spanning_tree_boruvka.py b/graphs/minimum_spanning_tree_boruvka.py
index 8ef8f6b7c827..fcbb4a7ff366 100644
--- a/graphs/minimum_spanning_tree_boruvka.py
+++ b/graphs/minimum_spanning_tree_boruvka.py
@@ -167,9 +167,9 @@ def boruvka_mst(graph) -> "Graph":
         union_find = Graph.UnionFind()
         mst_edges = []
         while num_components > 1:
-            cheap_edge = {}
-            for vertex in graph.get_vertices():
-                cheap_edge[vertex] = -1
+            cheap_edge: dict[int, list[int] | None] = dict.fromkeys(
+                graph.get_vertices()
+            )
 
             edges = graph.get_edges()
             for edge in edges:
@@ -180,13 +180,12 @@ def boruvka_mst(graph) -> "Graph":
                 set1 = union_find.find(head)
                 set2 = union_find.find(tail)
                 if set1 != set2:
-                    if cheap_edge[set1] == -1 or cheap_edge[set1][2] > weight:
-                        cheap_edge[set1] = [head, tail, weight]
-
-                    if cheap_edge[set2] == -1 or cheap_edge[set2][2] > weight:
-                        cheap_edge[set2] = [head, tail, weight]
+                    for component in (set1, set2):
+                        current = cheap_edge[component]
+                        if current is None or current[2] > weight:
+                            cheap_edge[component] = [head, tail, weight]
             for head_tail_weight in cheap_edge.values():
-                if head_tail_weight != -1:
+                if head_tail_weight is not None:
                     head, tail, weight = head_tail_weight
                     if union_find.find(head) != union_find.find(tail):
                         union_find.union(head, tail)
diff --git a/pyproject.toml b/pyproject.toml
index 52bd60b9d3aa..03c5d234303f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -321,7 +321,6 @@ rules.deprecated = "ignore"
 rules.invalid-argument-type = "ignore"
 rules.invalid-return-type = "ignore"
 rules.no-matching-overload = "ignore"
-rules.not-iterable = "ignore"
 rules.not-subscriptable = "ignore"
 rules.parameter-already-assigned = "ignore"
 rules.unresolved-attribute = "ignore"