From dd8ef3d37fbcc4569ac785bbbeba9f036f644d60 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Mart=C3=AD?= <mvdan@mvdan.cc>
Date: Wed, 27 May 2026 10:46:01 +0100
Subject: [PATCH] cue/testdata: add test for issue #4091
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The bug is resolved as of master; add a regression test.

Closes #4091.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I1dbe8f1a7d8a234397d1198db3a5d8132385417d
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1237927
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
---
 cue/testdata/comprehensions/issue4091.txtar   | 36 ++++++++++
 .../sync/comprehensions/issue4091.txtar       | 71 +++++++++++++++++++
 2 files changed, 107 insertions(+)
 create mode 100644 cue/testdata/comprehensions/issue4091.txtar
 create mode 100644 internal/core/compile/testdata/sync/comprehensions/issue4091.txtar

diff --git a/cue/testdata/comprehensions/issue4091.txtar b/cue/testdata/comprehensions/issue4091.txtar
new file mode 100644
index 000000000..05125f15d
--- /dev/null
+++ b/cue/testdata/comprehensions/issue4091.txtar
@@ -0,0 +1,36 @@
+# evalv3 incorrectly reported a "cyclic reference to field" error when a
+# comprehension-based field (_volumes) was conditionally exposed (volumes)
+# and then referenced through a generator pattern that re-binds the struct
+# via {_input: _obj}.
+# https://cuelang.org/issue/4091
+-- in.cue --
+output: (_Generator & {_input: _obj})._output @test(eq, {
+	genID: "id1"
+	_id: "id1"
+	volumeMounts: [{name: "mount1"}]
+	_volumes: {mount1: {name: "mount1"}}
+	volumes: {mount1: {name: "mount1"}}
+})
+
+_obj: spec: {
+	_id: "id1"
+	volumeMounts: [{name: "mount1"}]
+	_volumes: {
+		for _, vm in spec.volumeMounts {
+			(vm.name): name: vm.name
+		}
+	}
+	if len(_volumes) > 0 {
+		volumes: _volumes
+	}
+}
+_Generator: {
+	_input: {...}
+	_output: _input.spec
+	if _input.spec._id != _|_ {
+		_output: genID: (_input.spec._id)
+	}
+}
+-- out/errors.txt --
+[incomplete] _Generator._output: undefined field: spec:
+    ./in.cue:23:18
diff --git a/internal/core/compile/testdata/sync/comprehensions/issue4091.txtar b/internal/core/compile/testdata/sync/comprehensions/issue4091.txtar
new file mode 100644
index 000000000..59b02835b
--- /dev/null
+++ b/internal/core/compile/testdata/sync/comprehensions/issue4091.txtar
@@ -0,0 +1,71 @@
+# evalv3 incorrectly reported a "cyclic reference to field" error when a
+# comprehension-based field (_volumes) was conditionally exposed (volumes)
+# and then referenced through a generator pattern that re-binds the struct
+# via {_input: _obj}.
+# https://cuelang.org/issue/4091
+-- in.cue --
+output: (_Generator & {_input: _obj})._output @test(eq, {
+	genID: "id1"
+	_id: "id1"
+	volumeMounts: [{name: "mount1"}]
+	_volumes: {mount1: {name: "mount1"}}
+	volumes: {mount1: {name: "mount1"}}
+})
+
+_obj: spec: {
+	_id: "id1"
+	volumeMounts: [{name: "mount1"}]
+	_volumes: {
+		for _, vm in spec.volumeMounts {
+			(vm.name): name: vm.name
+		}
+	}
+	if len(_volumes) > 0 {
+		volumes: _volumes
+	}
+}
+_Generator: {
+	_input: {...}
+	_output: _input.spec
+	if _input.spec._id != _|_ {
+		_output: genID: (_input.spec._id)
+	}
+}
+-- out/compile --
+--- in.cue
+{
+  output: (〈0;_Generator〉 & {
+    _input: 〈1;_obj〉
+  })._output
+  _obj: {
+    spec: {
+      _id: "id1"
+      volumeMounts: [
+        {
+          name: "mount1"
+        },
+      ]
+      _volumes: {
+        for _, vm in 〈2;spec〉.volumeMounts {
+          〈1;vm〉.name: {
+            name: 〈2;vm〉.name
+          }
+        }
+      }
+      if (len(〈0;_volumes〉) > 0) {
+        volumes: 〈1;_volumes〉
+      }
+    }
+  }
+  _Generator: {
+    _input: {
+      ...
+    }
+    _output: 〈0;_input〉.spec
+    if (〈0;_input〉.spec._id != _|_(explicit error (_|_ literal) in source)) {
+      _output: {
+        genID: 〈2;_input〉.spec._id
+      }
+    }
+  }
+}
-- 
2.51.2