Don't restore active span if closed in withContext

When a span gets closed for whatever reason before getting restored in a
withContext callback, do not restore it. We do not restore closed spans
as active spans.

This is difficult to test, because the `active()` function also does
this check, but removing that check this test will still pass.

packages/nodejs/.changesets/do-not-restore-closed-spans-from-within-withspan.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "change"
+---
+
+Do not restore closed spans from within the `withSpan` helper. If a previously active span gets closed while `withSpan` has another span as currently active, do not restore the closed span when the callback has finished.

packages/nodejs/src/__tests__/scope.test.ts

@@ -253,6 +253,26 @@ describe("ScopeManager", () => {
       expect(scopeManager.active()).toBe(outerRootSpan)
       expect(scopeManager.root()).toBe(innerRootSpan)
     })
+
+    it("does not restore the active span if it is closed", () => {
+      const rootSpan = new RootSpan()
+      const activeSpan1 = new ChildSpan(rootSpan)
+      const activeSpan2 = new ChildSpan(rootSpan)
+
+      scopeManager.setRoot(rootSpan)
+      expect(scopeManager.active()).toBe(rootSpan)
+
+      scopeManager.withContext(activeSpan1, () => {
+        expect(scopeManager.active()).toBe(activeSpan1)
+        scopeManager.withContext(activeSpan2, () => {
+          activeSpan1.close()
+          expect(scopeManager.active()).toBe(activeSpan2)
+        })
+        expect(scopeManager.active()).toBeUndefined()
+      })
+
+      expect(scopeManager.active()).toBe(rootSpan)
+    })
   })
 
   describe(".bindContext()", () => {

packages/nodejs/src/scope.ts

@@ -194,10 +194,11 @@ export class ScopeManager {
       this.root()?.setError(err)
       throw err
     } finally {
-      // revert to the previous span
-      if (oldScope === undefined) {
-        this.#scopes.delete(uid)
-      } else {
+      // Unset the current active span so it doesn't leak outside this context
+      // in case there was no previous active span or it's no longer open.
+      this.#scopes.delete(uid)
+      if (oldScope && oldScope.open) {
+        // Revert the current active span
         this.#scopes.set(uid, oldScope)
       }
     }