From aa4c66cdfabea17210abe0a04a7b0ecff9723edf Mon Sep 17 00:00:00 2001
From: Beth Rennie <beth@brennie.ca>
Date: Sat, 6 Jun 2026 14:18:57 -0400
Subject: [PATCH] Bug 2045161 - Do not opt-out of unenrolled enrollments

---
 CHANGELOG.md                                   |  1 +
 components/nimbus/src/enrollment.rs            |  9 ++-------
 components/nimbus/src/tests/test_enrollment.rs | 16 ++++------------
 3 files changed, 7 insertions(+), 19 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 60d90a35c7..8c3fa41722 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 - Enrollment change events (visible to the UDL) now include the feature IDs of the features involved when possible. ([#7391](https://github.com/mozilla/application-services/pull/7391/))
 - Fixed a bug where enrollment change events were not emitted for rollouts that re-enrolled after previously unenrolling. ([#7391](https://github.com/mozilla/application-services/pull/7391/))
+- Attempting to opt-out from an experiment that is not currently enrolled is now a no-op. ([#7399](https://github.com/mozilla/application-services/pull/7399))
 
 [Full Changelog](In progress)
 
diff --git a/components/nimbus/src/enrollment.rs b/components/nimbus/src/enrollment.rs
index 32eca71a5c..1f1f2791ba 100644
--- a/components/nimbus/src/enrollment.rs
+++ b/components/nimbus/src/enrollment.rs
@@ -484,13 +484,8 @@ impl ExperimentEnrollment {
                 out_enrollment_events.push(enrollment.get_change_event(experiment));
                 enrollment
             }
-            EnrollmentStatus::NotEnrolled { .. } => Self {
-                slug: self.slug.to_string(),
-                status: EnrollmentStatus::NotEnrolled {
-                    reason: NotEnrolledReason::OptOut, // Explicitly set the reason to OptOut.
-                },
-            },
-            EnrollmentStatus::Disqualified { .. }
+            EnrollmentStatus::NotEnrolled { .. }
+            | EnrollmentStatus::Disqualified { .. }
             | EnrollmentStatus::WasEnrolled { .. }
             | EnrollmentStatus::Error { .. } => {
                 // Nothing to do here.
diff --git a/components/nimbus/src/tests/test_enrollment.rs b/components/nimbus/src/tests/test_enrollment.rs
index b787c92b8a..88720ed5e8 100644
--- a/components/nimbus/src/tests/test_enrollment.rs
+++ b/components/nimbus/src/tests/test_enrollment.rs
@@ -3749,11 +3749,9 @@ fn test_enrollment_enrolled_explicit_opt_out() {
         #[cfg(feature = "stateful")]
         None,
     );
-    if let EnrollmentStatus::Disqualified { branch, .. } = enrollment.status {
-        assert_eq!(branch, "control");
-    } else {
-        panic!("Wrong variant!");
-    }
+    assert!(
+        matches!(enrollment.status, EnrollmentStatus::Disqualified { branch, .. } if branch == "control")
+    );
     assert_eq!(
         &events,
         &[EnrollmentChangeEvent {
@@ -3782,13 +3780,7 @@ fn test_enrollment_not_enrolled_explicit_opt_out() {
         #[cfg(feature = "stateful")]
         None,
     );
-    assert!(matches!(
-        enrollment.status,
-        EnrollmentStatus::NotEnrolled {
-            reason: NotEnrolledReason::OptOut,
-            ..
-        }
-    ));
+    assert_eq!(enrollment, existing_enrollment);
     assert_eq!(&events, &[]);
 }