From f5661b73d9f21c4073818d550e19f8ed5286fdaa Mon Sep 17 00:00:00 2001
From: dorimedini-starkware <dori@starkware.co>
Date: Wed, 22 Jan 2025 09:44:50 +0200
Subject: [PATCH] feat(ci): add parent_branch.txt, make sure it's on the merge
 path (#3564)

---
 scripts/merge_branches.py   |  2 +-
 scripts/merge_paths_test.py | 27 ++++++++++++++++++++++-----
 scripts/parent_branch.txt   |  1 +
 3 files changed, 24 insertions(+), 6 deletions(-)
 create mode 100644 scripts/parent_branch.txt

diff --git a/scripts/merge_branches.py b/scripts/merge_branches.py
index 7c43f477dc..40d592fd1b 100755
--- a/scripts/merge_branches.py
+++ b/scripts/merge_branches.py
@@ -17,7 +17,7 @@
 
 FINAL_BRANCH = "main"
 MERGE_PATHS_FILE = "scripts/merge_paths.json"
-FILES_TO_PRESERVE = {"rust-toolchain.toml"}
+FILES_TO_PRESERVE = {"rust-toolchain.toml", "scripts/parent_branch.txt"}
 
 
 def load_merge_paths() -> Dict[str, str]:
diff --git a/scripts/merge_paths_test.py b/scripts/merge_paths_test.py
index 3b083904cb..e98272b6f9 100755
--- a/scripts/merge_paths_test.py
+++ b/scripts/merge_paths_test.py
@@ -1,9 +1,20 @@
+import pytest
+from typing import Dict
+
 from merge_branches import FINAL_BRANCH, MERGE_PATHS_FILE, load_merge_paths
 
 
-def test_linear_path():
-    merge_paths = load_merge_paths()
+@pytest.fixture
+def parent_branch() -> str:
+    return open("scripts/parent_branch.txt").read().strip()
+
+
+@pytest.fixture
+def merge_paths() -> Dict[str, str]:
+    return load_merge_paths()
 
+
+def test_linear_path(merge_paths: Dict[str, str]):
     src_dst_iter = iter(merge_paths.items())
     (oldest_branch, prev_dst_branch) = next(src_dst_iter)
     assert (
@@ -11,9 +22,7 @@ def test_linear_path():
     ), f"Oldest branch '{oldest_branch}' cannot be a destination branch."
 
     for src_branch, dst_branch in src_dst_iter:
-        assert (
-            prev_dst_branch == src_branch
-        ), (
+        assert prev_dst_branch == src_branch, (
             f"Since the merge graph is linear, the source branch '{src_branch}' must be the same "
             f"as the previous destination branch, which is '{prev_dst_branch}'. Check out "
             f"{MERGE_PATHS_FILE}."
@@ -23,3 +32,11 @@ def test_linear_path():
     assert (
         prev_dst_branch == FINAL_BRANCH
     ), f"The last destination is '{prev_dst_branch}' but must be '{FINAL_BRANCH}'."
+
+
+def test_parent_branch_is_on_path(parent_branch: str, merge_paths: Dict[str, str]):
+    known_branches = set(merge_paths.keys()) | set(merge_paths.values())
+    assert parent_branch in known_branches, (
+        f"Parent branch '{parent_branch}' is not on the merge path (branches in merge path: "
+        f"{known_branches})."
+    )
diff --git a/scripts/parent_branch.txt b/scripts/parent_branch.txt
new file mode 100644
index 0000000000..ba2906d066
--- /dev/null
+++ b/scripts/parent_branch.txt
@@ -0,0 +1 @@
+main