From ff3e75fe5ea8d439f87842d6289d7d331aa8290e Mon Sep 17 00:00:00 2001
From: Sergii <sergiy.stotskiy@gmail.com>
Date: Tue, 17 Aug 2021 11:41:12 +0300
Subject: [PATCH] fix(ability): makes sure that other event handlers are not
 lost when last handler is unregistered

---
 packages/casl-ability/spec/ability.spec.js | 30 +++++++++++++++++-----
 packages/casl-ability/src/RuleIndex.ts     | 14 ++++++----
 2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/packages/casl-ability/spec/ability.spec.js b/packages/casl-ability/spec/ability.spec.js
index 7afc97680..3dd32698b 100755
--- a/packages/casl-ability/spec/ability.spec.js
+++ b/packages/casl-ability/spec/ability.spec.js
@@ -221,25 +221,41 @@ describe('Ability', () => {
           spy(() => results.push(0)),
           spy(() => results.push(1)),
           spy(() => results.push(2)),
-          spy(() => results.push(3))
         ]
         const unsubscribe = []
 
         unsubscribe[0] = ability.on('updated', handlers[0])
         unsubscribe[1] = ability.on('updated', handlers[1])
-        unsubscribe[2] = ability.on('updated', handlers[2])
-        unsubscribe[3] = ability.on('updated', () => {
-          handlers[3]()
-          unsubscribe[2]()
+        unsubscribe[2] = ability.on('updated', () => {
+          handlers[2]()
+          unsubscribe[1]()
         })
         ability.update([])
 
-        expect(results).to.deep.equal([3, 2, 1, 0])
+        expect(results).to.deep.equal([2, 1, 0])
 
         results = []
         ability.update([{ action: 'read', subject: 'all' }])
 
-        expect(results).to.deep.equal([3, 1, 0])
+        expect(results).to.deep.equal([2, 0])
+      })
+
+      it('can unregister last handler', () => {
+        let results = []
+        const handlers = [
+          spy(() => results.push(0)),
+          spy(() => results.push(1)),
+          spy(() => results.push(2)),
+        ]
+        const unsubscribe = []
+
+        unsubscribe[0] = ability.on('updated', handlers[0])
+        unsubscribe[1] = ability.on('updated', handlers[1])
+        unsubscribe[2] = ability.on('updated', handlers[2])
+        unsubscribe[2]();
+        ability.update([])
+
+        expect(results).to.deep.equal([1, 0])
       })
     })
   })
diff --git a/packages/casl-ability/src/RuleIndex.ts b/packages/casl-ability/src/RuleIndex.ts
index 3126111b5..5b137d71d 100644
--- a/packages/casl-ability/src/RuleIndex.ts
+++ b/packages/casl-ability/src/RuleIndex.ts
@@ -218,16 +218,20 @@ export class RuleIndex<A extends Abilities, Conditions> {
     event: T,
     handler: EventsMap<Public<this>>[T]
   ): Unsubscribe {
-    const head = this._events.get(event) || null;
-    const item = linkedItem(handler, head);
+    const tail = this._events.get(event) || null;
+    const item = linkedItem(handler, tail);
     this._events.set(event, item);
 
     return () => {
-      if (!item.next && !item.prev && this._events.get(event) === item) {
+      const currentTail = this._events.get(event);
+
+      if (!item.next && !item.prev && currentTail === item) {
         this._events.delete(event);
-      } else {
-        unlinkItem(item);
+      } else if (item === currentTail) {
+        this._events.set(event, item.prev);
       }
+
+      unlinkItem(item);
     };
   }