From 6d01dc18724dcd896bb7d474529d34fe8f0fe34b Mon Sep 17 00:00:00 2001
From: Sergio Garcia <47090312+singiamtel@users.noreply.github.com>
Date: Tue, 3 Jun 2025 15:08:55 +0200
Subject: [PATCH] Find cycles in recipes (#917)

---
 bits_helpers/utilities.py | 21 +++++++++++++++++++++
 tests/test_utilities.py   | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/bits_helpers/utilities.py b/bits_helpers/utilities.py
index 1c929c41..e4e6f510 100644
--- a/bits_helpers/utilities.py
+++ b/bits_helpers/utilities.py
@@ -64,6 +64,27 @@ def topological_sort(specs):
     edges = [(pkg, dep) for pkg, dep in edges if dep != current_package]
     # ...but keep blocking those that still depend on other stuff!
     leaves.extend(new_leaves - {pkg for pkg, _ in edges})
+  # If we have any edges left, we have a cycle
+  if edges:
+    # Find a cycle by following dependencies
+    cycle = []
+    start = edges[0][0]  # Start with any remaining package
+    current = start
+    max_iter = 10000 # Prevent infinite loops
+    while max_iter > 0:
+      max_iter -= 1
+      cycle.append(current)
+      # Find what current depends on
+      for pkg, dep in edges:
+        if pkg == current:
+          current = dep
+          break
+      if current in cycle:  # We found a cycle
+        cycle = cycle[cycle.index(current):]  # Trim to just the cycle
+        dieOnError(True, "Dependency cycle detected: " + " -> ".join(cycle + [cycle[0]]))
+      if current == start:  # We've gone full circle
+        raise RuntimeError("Internal error: cycle detection failed")
+    assert False, "Unreachable error: cycle detection failed"
 
 
 def resolve_store_path(architecture, spec_hash):
diff --git a/tests/test_utilities.py b/tests/test_utilities.py
index 1016f410..c8f2c321 100644
--- a/tests/test_utilities.py
+++ b/tests/test_utilities.py
@@ -5,12 +5,14 @@
 # Assuming you are using the mock library to ... mock things
 from unittest.mock import patch
 
-from bits_helpers.utilities import doDetectArch, filterByArchitectureDefaults, disabledByArchitectureDefaults
+from bits_helpers.utilities import doDetectArch, filterByArchitectureDefaults, disabledByArchitectureDefaults, getPkgDirs
 from bits_helpers.utilities import Hasher
 from bits_helpers.utilities import asList
 from bits_helpers.utilities import prunePaths
 from bits_helpers.utilities import resolve_version
 from bits_helpers.utilities import topological_sort
+from bits_helpers.utilities import resolveFilename, resolveDefaultsFilename
+import bits_helpers
 import os
 import string
 
@@ -272,6 +274,39 @@ def test_dont_drop_packages(self) -> None:
         self.assertEqual(frozenset(specs.keys()),
                          frozenset(topological_sort(specs)))
 
+    def test_cycle(self) -> None:
+        """Test that dependency cycles are detected and reported."""
+        specs = {
+            "A": {"package": "A", "requires": ["B"]},
+            "B": {"package": "B", "requires": ["C"]},
+            "C": {"package": "C", "requires": ["D"]},
+            "D": {"package": "D", "requires": ["A"]}
+        }
+        with patch.object(alibuild_helpers.log, 'error') as mock_error:
+          with self.assertRaises(SystemExit) as cm:
+            list(topological_sort(specs))
+          self.assertEqual(cm.exception.code, 1)
+          mock_error.assert_called_once_with("%s", "Dependency cycle detected: A -> B -> C -> D -> A")
+
+    def test_empty_set(self) -> None:
+        """Test that an empty set of packages is handled correctly."""
+        self.assertEqual([], list(topological_sort({})))
+        
+    def test_single_package(self) -> None:
+        """Test that a single package with no dependencies is handled correctly."""
+        self.assertEqual(["A"], list(topological_sort({
+            "A": {"package": "A", "requires": []}
+        })))
+        
+    def test_independent_packages(self) -> None:
+        """Test that packages with no dependencies between them are handled correctly."""
+        result = list(topological_sort({
+            "A": {"package": "A", "requires": []},
+            "B": {"package": "B", "requires": []},
+            "C": {"package": "C", "requires": []}
+        }))
+        self.assertEqual(set(["A", "B", "C"]), set(result))
+        self.assertEqual(3, len(result))
 
 if __name__ == '__main__':
     unittest.main()