feat(cohorts): add used-in references endpoint and UI

frontend/src/scenes/cohorts/CohortEdit.tsx

@@ -38,7 +38,7 @@ import {
 } from '~/layout/scenes/SceneLayout'
 import { AndOrFilterSelect } from '~/queries/nodes/InsightViz/PropertyGroupFilters/AndOrFilterSelect'
 import { Query } from '~/queries/Query/Query'
-import { CohortType, SidePanelTab } from '~/types'
+import { CohortType, InsightShortId, SidePanelTab } from '~/types'
 
 import { AddPersonToCohortModal } from './AddPersonToCohortModal'
 import { addPersonToCohortModalLogic } from './addPersonToCohortModalLogic'
@@ -96,6 +96,7 @@ export function CohortEdit({ id, attachTo, tabId }: CohortEditProps): JSX.Elemen
         canRemovePersonFromCohort,
         isPendingCalculation,
         isCalculatingOrPending,
+        usedIn,
         staticCohortMode,
     } = useValues(logic)
     const { featureFlags } = useValues(featureFlagLogic)
@@ -564,6 +565,71 @@ export function CohortEdit({ id, attachTo, tabId }: CohortEditProps): JSX.Elemen
                                         </Link>
                                     </LemonBanner>
                                 )}
+                                {!isNewCohort &&
+                                    usedIn &&
+                                    (usedIn.feature_flags.length > 0 ||
+                                        usedIn.insights.results.length > 0 ||
+                                        usedIn.cohorts.results.length > 0) && (
+                                        <LemonBanner type="info">
+                                            <div className="font-semibold mb-1">Used in</div>
+                                            <div className="space-y-2">
+                                                {usedIn.feature_flags.length > 0 && (
+                                                    <div>
+                                                        <div className="text-xs font-semibold uppercase opacity-60">
+                                                            Feature flags
+                                                        </div>
+                                                        <ul className="list-disc pl-4 mb-0 space-y-0.5">
+                                                            {usedIn.feature_flags.map((flag) => (
+                                                                <li key={`flag-${flag.id}`}>
+                                                                    <Link to={urls.featureFlag(flag.id)}>
+                                                                        {flag.name || flag.key}
+                                                                    </Link>
+                                                                </li>
+                                                            ))}
+                                                        </ul>
+                                                    </div>
+                                                )}
+                                                {usedIn.insights.results.length > 0 && (
+                                                    <div>
+                                                        <div className="text-xs font-semibold uppercase opacity-60">
+                                                            Insights
+                                                            {usedIn.insights.has_more &&
+                                                                ` (${usedIn.insights.results.length} of ${usedIn.insights.total} shown)`}
+                                                        </div>
+                                                        <ul className="list-disc pl-4 mb-0 space-y-0.5">
+                                                            {usedIn.insights.results.map((insight) => (
+                                                                <li key={`insight-${insight.id}`}>
+                                                                    <Link
+                                                                        to={urls.insightView(
+                                                                            insight.short_id as InsightShortId
+                                                                        )}
+                                                                    >
+                                                                        {insight.name}
+                                                                    </Link>
+                                                                </li>
+                                                            ))}
+                                                        </ul>
+                                                    </div>
+                                                )}
+                                                {usedIn.cohorts.results.length > 0 && (
+                                                    <div>
+                                                        <div className="text-xs font-semibold uppercase opacity-60">
+                                                            Cohorts
+                                                            {usedIn.cohorts.has_more &&
+                                                                ` (${usedIn.cohorts.results.length} of ${usedIn.cohorts.total} shown)`}
+                                                        </div>
+                                                        <ul className="list-disc pl-4 mb-0 space-y-0.5">
+                                                            {usedIn.cohorts.results.map((c) => (
+                                                                <li key={`cohort-${c.id}`}>
+                                                                    <Link to={urls.cohort(c.id)}>{c.name}</Link>
+                                                                </li>
+                                                            ))}
+                                                        </ul>
+                                                    </div>
+                                                )}
+                                            </div>
+                                        </LemonBanner>
+                                    )}
                                 <SceneSection
                                     // TODO: @adamleithp Add a number of matching persons to the title "Matching criteria (100)"
                                     title="Matching criteria"

frontend/src/scenes/cohorts/cohortEditLogic.ts

@@ -24,6 +24,7 @@ import {
     validateGroup,
 } from 'scenes/cohorts/cohortUtils'
 import { personsLogic } from 'scenes/persons/personsLogic'
+import { teamLogic } from 'scenes/teamLogic'
 import { urls } from 'scenes/urls'
 
 import { refreshTreeItem } from '~/layout/panel-layout/ProjectTree/projectTreeLogic'
@@ -45,6 +46,9 @@ import {
     PropertyType,
 } from '~/types'
 
+import { cohortsUsedInRetrieve } from 'products/cohorts/frontend/generated/api'
+import type { CohortUsedInResponseApi } from 'products/cohorts/frontend/generated/api.schemas'
+
 import type { cohortEditLogicType } from './cohortEditLogicType'
 
 export type CohortLogicProps = {
@@ -83,6 +87,7 @@ export const cohortEditLogic = kea<cohortEditLogicType>([
     }),
     path(['scenes', 'cohorts', 'cohortLogicEdit']),
     connect(() => ({
+        values: [teamLogic, ['currentProjectId']],
         actions: [eventUsageLogic, ['reportExperimentExposureCohortEdited']],
         logic: [cohortsModel],
     })),
@@ -566,6 +571,24 @@ export const cohortEditLogic = kea<cohortEditLogicType>([
                 },
             },
         ],
+
+        usedIn: [
+            null as CohortUsedInResponseApi | null,
+            {
+                loadUsedIn: async () => {
+                    const { id } = values.cohort
+                    if (!id || id === 'new') {
+                        return null
+                    }
+                    try {
+                        return await cohortsUsedInRetrieve(String(values.currentProjectId), id)
+                    } catch (error) {
+                        posthog.captureException(error, { feature: 'cohort-used-in' })
+                        return null
+                    }
+                },
+            },
+        ],
     })),
     listeners(({ actions, values }) => ({
         setCriteria: ({ newCriteria, groupIndex, criteriaIndex }) => {
@@ -613,6 +636,9 @@ export const cohortEditLogic = kea<cohortEditLogicType>([
                     'There was an error submitting this cohort. Make sure the cohort filters are correct.',
             })
         },
+        submitCohortSuccess: () => {
+            actions.loadUsedIn()
+        },
         checkIfFinishedCalculating: async ({ cohort }, breakpoint) => {
             const isPendingCalculation = checkIsPendingCalculation(cohort)
             const isCalculatingOrPending = cohort.is_calculating || isPendingCalculation
@@ -658,6 +684,7 @@ export const cohortEditLogic = kea<cohortEditLogicType>([
             actions.setCohort(NEW_COHORT)
         } else {
             actions.fetchCohort(props.id)
+            actions.loadUsedIn()
         }
     }),
     beforeUnmount(({ values }) => {

posthog/api/cohort.py

@@ -382,6 +382,54 @@ class RemovePersonRequestSerializer(serializers.Serializer):
     person_id = serializers.UUIDField(required=True, help_text="Person UUID to remove from the cohort")
 
 
+class CohortUsedInFlagSerializer(serializers.Serializer):
+    id = serializers.IntegerField(help_text="Feature flag database ID")
+    key = serializers.CharField(help_text="Feature flag key (URL slug)")
+    name = serializers.CharField(allow_null=True, allow_blank=True, help_text="Feature flag display name")
+
+
+class CohortUsedInInsightSerializer(serializers.Serializer):
+    id = serializers.IntegerField(help_text="Insight database ID")
+    short_id = serializers.CharField(help_text="Insight short ID used for routing in the frontend")
+    name = serializers.CharField(
+        help_text="Insight display name; falls back to derived name, then to 'Unnamed' when both are empty"
+    )
+
+
+class CohortUsedInCohortSerializer(serializers.Serializer):
+    id = serializers.IntegerField(help_text="Cohort database ID")
+    name = serializers.CharField(help_text="Cohort display name")
+
+
+class CohortUsedInInsightsBlockSerializer(serializers.Serializer):
+    results = CohortUsedInInsightSerializer(
+        many=True, help_text="Insights referencing this cohort, capped at 100 results"
+    )
+    total = serializers.IntegerField(help_text="Total number of insights referencing this cohort, before truncation")
+    has_more = serializers.BooleanField(help_text="True when more insights exist beyond the truncation cap")
+
+
+class CohortUsedInCohortsBlockSerializer(serializers.Serializer):
+    results = CohortUsedInCohortSerializer(
+        many=True, help_text="Cohorts that include this cohort as a criterion, capped at 100 results"
+    )
+    total = serializers.IntegerField(help_text="Total number of cohorts referencing this cohort, before truncation")
+    has_more = serializers.BooleanField(help_text="True when more cohorts exist beyond the truncation cap")
+
+
+class CohortUsedInResponseSerializer(serializers.Serializer):
+    feature_flags = CohortUsedInFlagSerializer(
+        many=True,
+        help_text="Feature flags (active and inactive, excluding soft-deleted) that reference this cohort in their targeting conditions",
+    )
+    insights = CohortUsedInInsightsBlockSerializer(
+        help_text="Insights referencing this cohort with truncation metadata"
+    )
+    cohorts = CohortUsedInCohortsBlockSerializer(
+        help_text="Other cohorts that include this cohort as a criterion, with truncation metadata"
+    )
+
+
 class CohortCalculationHistorySerializer(serializers.ModelSerializer):
     duration_seconds = serializers.ReadOnlyField()
     is_completed = serializers.ReadOnlyField()
@@ -976,8 +1024,7 @@ def update(self, cohort: Cohort, validated_data: dict, *args: Any, **kwargs: Any
         is_deletion_change = deleted_state is not None and cohort.deleted != deleted_state
         if is_deletion_change:
             if deleted_state:
-                flags_using_cohort = FeatureFlag.objects.filter(team__project_id=cohort.team.project_id, active=True)
-                flags_with_cohort = [flag for flag in flags_using_cohort if cohort.id in flag.get_cohort_ids()]
+                flags_with_cohort = get_active_flags_using_cohort(cohort)
                 if flags_with_cohort:
                     flag_names = [flag.name or flag.key for flag in flags_with_cohort]
                     raise ValidationError(
@@ -1005,21 +1052,7 @@ def update(self, cohort: Cohort, validated_data: dict, *args: Any, **kwargs: Any
                     )
 
                 # Check if cohort is used in insights
-
-                # Use PostgreSQL's jsonb_path_exists for recursive JSONB searching
-                # This finds cohort references at any depth in the JSON structure
-                # nosemgrep: python.django.security.audit.query-set-extra.avoid-query-set-extra (parameterized via params)
-                insights_using_cohort = Insight.objects.filter(
-                    team_id=cohort.team_id,
-                    deleted=False,
-                ).extra(
-                    where=[
-                        """jsonb_path_exists(query, '$.** ? (@.type == "cohort" && @.value == %s)', '{"cohort_id": %s}'::jsonb)
-                        OR (query->'source'->'breakdownFilter'->>'breakdown_type' = 'cohort'
-                            AND query->'source'->'breakdownFilter'->'breakdown' @> '[%s]'::jsonb)"""
-                    ],
-                    params=[cohort.id, cohort.id, cohort.id],
-                )
+                insights_using_cohort = get_insights_using_cohort(cohort)
 
                 if insights_using_cohort.exists():
                     count = insights_using_cohort.count()
@@ -1035,24 +1068,11 @@ def update(self, cohort: Cohort, validated_data: dict, *args: Any, **kwargs: Any
                     )
 
                 # Check if cohort is used as criteria in other cohorts
-                # nosemgrep: python.django.security.audit.query-set-extra.avoid-query-set-extra (parameterized via params)
-                dependent_cohorts = (
-                    Cohort.objects.filter(
-                        team__project_id=cohort.team.project_id,
-                        deleted=False,
-                    )
-                    .exclude(id=cohort.id)
-                    .extra(
-                        where=[
-                            """jsonb_path_exists(filters, '$.** ? (@.type == "cohort" && @.value == %s)', '{"cohort_id": %s}'::jsonb)"""
-                        ],
-                        params=[cohort.id, cohort.id],
-                    )
-                )
+                dependent_cohorts = get_cohorts_using_cohort(cohort)
 
                 if dependent_cohorts.exists():
                     count = dependent_cohorts.count()
-                    cohort_names = [c.name for c in dependent_cohorts[:5]]
+                    cohort_names = [c.name or "Unnamed" for c in dependent_cohorts[:5]]
                     names_str = ", ".join(cohort_names)
                     if count > 5:
                         names_str = f"{names_str}, and {count - 5} more"
@@ -1126,6 +1146,63 @@ def to_representation(self, instance):
         return representation
 
 
+COHORT_USED_IN_PAGE_SIZE = 100
+
+
+def get_active_flags_using_cohort(cohort: Cohort) -> list[FeatureFlag]:
+    """Return active, non-deleted feature flags that reference this cohort.
+
+    Used by deletion protection — only live flags should block cohort deletion.
+    """
+    active_flags = FeatureFlag.objects.filter(team__project_id=cohort.team.project_id, active=True, deleted=False)
+    return [flag for flag in active_flags if cohort.id in flag.get_cohort_ids()]
+
+
+def get_flags_using_cohort(cohort: Cohort) -> list[FeatureFlag]:
+    """Return all non-deleted feature flags (active or inactive) that reference this cohort.
+
+    Used by the informational ``used_in`` endpoint — surfaces inactive flags too so users
+    are aware before flipping one back on. Excludes soft-deleted flags for consistency
+    with ``get_insights_using_cohort`` and ``get_cohorts_using_cohort``.
+    """
+    flags = FeatureFlag.objects.filter(team__project_id=cohort.team.project_id, deleted=False)
+    return [flag for flag in flags if cohort.id in flag.get_cohort_ids()]
+
+
+def get_insights_using_cohort(cohort: Cohort) -> QuerySet[Insight]:
+    """Return insights that reference this cohort in their query filters or breakdown."""
+    # nosemgrep: python.django.security.audit.query-set-extra.avoid-query-set-extra (parameterized via params)
+    return Insight.objects.filter(
+        team_id=cohort.team_id,
+        deleted=False,
+    ).extra(
+        where=[
+            """jsonb_path_exists(query, '$.** ? (@.type == "cohort" && @.value == %s)', '{"cohort_id": %s}'::jsonb)
+            OR (query->'source'->'breakdownFilter'->>'breakdown_type' = 'cohort'
+                AND query->'source'->'breakdownFilter'->'breakdown' @> '[%s]'::jsonb)"""
+        ],
+        params=[cohort.id, cohort.id, cohort.id],
+    )
+
+
+def get_cohorts_using_cohort(cohort: Cohort) -> QuerySet[Cohort]:
+    """Return other cohorts that include this cohort as criteria."""
+    # nosemgrep: python.django.security.audit.query-set-extra.avoid-query-set-extra (parameterized via params)
+    return (
+        Cohort.objects.filter(
+            team__project_id=cohort.team.project_id,
+            deleted=False,
+        )
+        .exclude(id=cohort.id)
+        .extra(
+            where=[
+                """jsonb_path_exists(filters, '$.** ? (@.type == "cohort" && @.value == %s)', '{"cohort_id": %s}'::jsonb)"""
+            ],
+            params=[cohort.id, cohort.id],
+        )
+    )
+
+
 @extend_schema(tags=["core"])
 class CohortViewSet(TeamAndOrgViewSetMixin, ForbidDestroyModel, viewsets.ModelViewSet):
     queryset = Cohort.objects.all()
@@ -1489,6 +1566,45 @@ def calculation_history(self, request: request.Request, **kwargs):
             }
         )
 
+    @extend_schema(responses=CohortUsedInResponseSerializer)
+    @action(methods=["GET"], detail=True, required_scopes=["cohort:read"])
+    def used_in(self, request: request.Request, **kwargs) -> Response:
+        cohort: Cohort = self.get_object()
+
+        flags_with_cohort = get_flags_using_cohort(cohort)
+        flags_data = [{"id": flag.id, "key": flag.key, "name": flag.name} for flag in flags_with_cohort]
+
+        insights_qs = get_insights_using_cohort(cohort)
+        insights_total = insights_qs.count()
+        insights_data = [
+            {
+                "id": insight["id"],
+                "short_id": insight["short_id"],
+                "name": insight.get("name") or insight.get("derived_name") or "Unnamed",
+            }
+            for insight in insights_qs.values("id", "short_id", "name", "derived_name")[:COHORT_USED_IN_PAGE_SIZE]
+        ]
+
+        cohorts_qs = get_cohorts_using_cohort(cohort)
+        cohorts_total = cohorts_qs.count()
+        cohorts_data = list(cohorts_qs.values("id", "name")[:COHORT_USED_IN_PAGE_SIZE])
+
+        return Response(
+            {
+                "feature_flags": flags_data,
+                "insights": {
+                    "results": insights_data,
+                    "total": insights_total,
+                    "has_more": insights_total > len(insights_data),
+                },
+                "cohorts": {
+                    "results": cohorts_data,
+                    "total": cohorts_total,
+                    "has_more": cohorts_total > len(cohorts_data),
+                },
+            }
+        )
+
     def perform_create(self, serializer):
         serializer.save()
         instance = cast(Cohort, serializer.instance)