From 312e90f4b6c8b5680117b56b4f80af85828c3cfd Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Sat, 9 Aug 2025 15:01:25 +0200
Subject: [PATCH] tests: add small testcase for output cycle detection

Change-Id: I186937dfbca4d051e5ad860239720816429a0a8e
---
 tests/functional/check-outputs.nix | 25 +++++++++++++++++++++++++
 tests/functional/meson.build       |  1 +
 tests/functional/output-cycles.sh  | 10 ++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 tests/functional/check-outputs.nix
 create mode 100644 tests/functional/output-cycles.sh

diff --git a/tests/functional/check-outputs.nix b/tests/functional/check-outputs.nix
new file mode 100644
index 000000000..ce260dd4d
--- /dev/null
+++ b/tests/functional/check-outputs.nix
@@ -0,0 +1,25 @@
+with import ./config.nix;
+
+rec {
+  dep = import ./dependencies.nix {};
+
+  cycle = mkDerivation {
+    name = "cycle";
+    inherit dep;
+    outputs = [ "foo" "bar" "baz" ];
+    builder = builtins.toFile "builder.sh" ''
+      mkdir -p $foo/bin $bar/lib $baz/share
+      echo $bar > $foo/bin/alarm
+      echo $baz > $bar/lib/libfoo
+      echo $foo > $baz/share/lalala
+    '';
+  };
+
+  as_dependency = mkDerivation {
+    name = "depends-on-cycle";
+    inherit cycle;
+    builder = builtins.toFile "builder.sh" ''
+      touch $out
+    '';
+  };
+}
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index c37a32e62..7b73ed26a 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -173,6 +173,7 @@ functional_tests_scripts = [
   'regression-reference-checks.sh',
   'redirected-filter-source.sh',
   'daemon-trust.sh',
+  'output-cycles.sh',
 ]
 
 # Plugin tests require shared libraries support.
diff --git a/tests/functional/output-cycles.sh b/tests/functional/output-cycles.sh
new file mode 100644
index 000000000..6b2931ba2
--- /dev/null
+++ b/tests/functional/output-cycles.sh
@@ -0,0 +1,10 @@
+source common.sh
+
+clearStore
+
+(! nix-build check-outputs.nix -A cycle) 2>&1 | grepQuiet "cycle detected in build of '.*' in the references of output 'bar' from output 'foo'"
+
+error="$(! nix-build check-outputs.nix -A as_dependency 2>&1)"
+
+grepQuiet "cycle detected in build of '.*' in the references of output 'bar' from output 'foo'" <<<"$error"
+grepQuiet "error: 1 dependencies of derivation" <<<"$error"