fix: returned operator functions from multicast operators share, publish, publishReplay are now referentially transparent. Meaning if you take the result of calling publish() and pass it to N observable pipe methods, it will behave the same in each case, rather than having a cumulative effect, which was a regression introduced sometime in 6.x. If you required this broken behavior, there is a work around posted [here](#6410 (comment)) (#6410)

* fix(publish,publishReplay): resolve sharing Subject

change publish operator to use factory
change publishReplay operator to not share ReplaySubject
fixes issue #5411

* test: rearrange tests

* test: add failing ref transparency tests

* fix(publishBehavior): make ref transparent

* fix(publishLast): make ref transparent

* test: add failing ref transparency tests

* fix(share): make ref transparent

* chore: add a comment

* test: change descriptions and add comments

* refactor: destructure options outside of op func

* chore: use consistent terminology in comments

* test: use consistent terminology

Co-authored-by: Eli Davidson <edavidson@broadfinancial.com>

Author: cartant

spec/operators/publish-spec.ts

@@ -1,7 +1,7 @@
 import { expect } from 'chai';
 import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
 import { publish, zip, mergeMapTo, mergeMap, tap, refCount, retry, repeat } from 'rxjs/operators';
-import { ConnectableObservable, of, Subscription, Observable } from 'rxjs';
+import { ConnectableObservable, of, Subscription, Observable, pipe } from 'rxjs';
 
 /** @test {publish} */
 describe('publish operator', () => {
@@ -337,4 +337,31 @@ describe('publish operator', () => {
     expect(subscriptions).to.equal(1);
     done();
   });
+
+  it('should be referentially-transparent', () => {
+    const source1 = cold('-1-2-3-4-5-|');
+    const source1Subs =  '^          !';
+    const expected1 =    '-1-2-3-4-5-|';
+    const source2 = cold('-6-7-8-9-0-|');
+    const source2Subs =  '^          !';
+    const expected2 =    '-6-7-8-9-0-|';
+
+    // Calls to the _operator_ must be referentially-transparent.
+    const partialPipeLine = pipe(
+      publish()
+    );
+
+    // The non-referentially-transparent publishing occurs within the _operator function_
+    // returned by the _operator_ and that happens when the complete pipeline is composed.
+    const published1 = source1.pipe(partialPipeLine) as ConnectableObservable<any>;
+    const published2 = source2.pipe(partialPipeLine) as ConnectableObservable<any>;
+
+    expectObservable(published1).toBe(expected1);
+    expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+    expectObservable(published2).toBe(expected2);
+    expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+
+    published1.connect();
+    published2.connect();
+  });
 });

spec/operators/publishBehavior-spec.ts

@@ -1,7 +1,7 @@
 import { expect } from 'chai';
 import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
 import { publishBehavior, mergeMapTo, tap, mergeMap, refCount, retry, repeat } from 'rxjs/operators';
-import { ConnectableObservable, of, Subscription, Observable } from 'rxjs';
+import { ConnectableObservable, of, Subscription, Observable, pipe } from 'rxjs';
 
 /** @test {publishBehavior} */
 describe('publishBehavior operator', () => {
@@ -344,4 +344,31 @@ describe('publishBehavior operator', () => {
     expect(results).to.deep.equal([]);
     done();
   });
+
+  it('should be referentially-transparent', () => {
+    const source1 = cold('-1-2-3-4-5-|');
+    const source1Subs =  '^          !';
+    const expected1 =    'x1-2-3-4-5-|';
+    const source2 = cold('-6-7-8-9-0-|');
+    const source2Subs =  '^          !'; 
+    const expected2 =    'x6-7-8-9-0-|';
+
+    // Calls to the _operator_ must be referentially-transparent.
+    const partialPipeLine = pipe(
+      publishBehavior('x')
+    );
+
+    // The non-referentially-transparent publishing occurs within the _operator function_
+    // returned by the _operator_ and that happens when the complete pipeline is composed.
+    const published1 = source1.pipe(partialPipeLine) as ConnectableObservable<any>;
+    const published2 = source2.pipe(partialPipeLine) as ConnectableObservable<any>;
+
+    expectObservable(published1).toBe(expected1);
+    expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+    expectObservable(published2).toBe(expected2);
+    expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+
+    published1.connect();
+    published2.connect();
+  });
 });

spec/operators/publishLast-spec.ts

@@ -1,7 +1,7 @@
 import { expect } from 'chai';
 import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
 import { publishLast, mergeMapTo, tap, mergeMap, refCount, retry } from 'rxjs/operators';
-import { ConnectableObservable, of, Subscription, Observable } from 'rxjs';
+import { ConnectableObservable, of, Subscription, Observable, pipe } from 'rxjs';
 
 /** @test {publishLast} */
 describe('publishLast operator', () => {
@@ -261,4 +261,31 @@ describe('publishLast operator', () => {
     expect(subscriptions).to.equal(1);
     done();
   });
+
+  it('should be referentially-transparent', () => {
+    const source1 = cold('-1-2-3-4-5-|');
+    const source1Subs =  '^          !';
+    const expected1 =    '-----------(5|)';
+    const source2 = cold('-6-7-8-9-0-|');
+    const source2Subs =  '^          !';
+    const expected2 =    '-----------(0|)';
+
+    // Calls to the _operator_ must be referentially-transparent.
+    const partialPipeLine = pipe(
+      publishLast()
+    );
+
+    // The non-referentially-transparent publishing occurs within the _operator function_
+    // returned by the _operator_ and that happens when the complete pipeline is composed.
+    const published1 = source1.pipe(partialPipeLine) as ConnectableObservable<any>;
+    const published2 = source2.pipe(partialPipeLine) as ConnectableObservable<any>;
+
+    expectObservable(published1).toBe(expected1);
+    expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+    expectObservable(published2).toBe(expected2);
+    expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+
+    published1.connect();
+    published2.connect();
+  });
 });

spec/operators/publishReplay-spec.ts

@@ -1,6 +1,6 @@
 import { expect } from 'chai';
 import { hot, cold, expectObservable, expectSubscriptions } from '../helpers/marble-testing';
-import { throwError, ConnectableObservable, EMPTY, NEVER, of, Observable, Subscription } from 'rxjs';
+import { throwError, ConnectableObservable, EMPTY, NEVER, of, Observable, Subscription, pipe } from 'rxjs';
 import { publishReplay, mergeMapTo, tap, mergeMap, refCount, retry, repeat, map } from 'rxjs/operators';
 
 /** @test {publishReplay} */
@@ -487,4 +487,31 @@ describe('publishReplay operator', () => {
     expectObservable(published).toBe(expected, undefined, error);
     expectSubscriptions(source.subscriptions).toBe(sourceSubs);
   });
+
+  it('should be referentially-transparent', () => {
+    const source1 = cold('-1-2-3-4-5-|');
+    const source1Subs =  '^          !';
+    const expected1 =    '-1-2-3-4-5-|';
+    const source2 = cold('-6-7-8-9-0-|');
+    const source2Subs =  '^          !';
+    const expected2 =    '-6-7-8-9-0-|';
+
+    // Calls to the _operator_ must be referentially-transparent.
+    const partialPipeLine = pipe(
+      publishReplay(1)
+    );
+
+    // The non-referentially-transparent publishing occurs within the _operator function_
+    // returned by the _operator_ and that happens when the complete pipeline is composed.
+    const published1 = source1.pipe(partialPipeLine) as ConnectableObservable<any>;
+    const published2 = source2.pipe(partialPipeLine) as ConnectableObservable<any>;
+
+    expectObservable(published1).toBe(expected1);
+    expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+    expectObservable(published2).toBe(expected2);
+    expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+
+    published1.connect();
+    published2.connect();
+  });
 });

spec/operators/share-spec.ts

@@ -1,6 +1,6 @@
 /** @prettier */
 import { expect } from 'chai';
-import { asapScheduler, concat, config, defer, EMPTY, NEVER, Observable, of, scheduled, Subject, throwError } from 'rxjs';
+import { asapScheduler, concat, config, defer, EMPTY, NEVER, Observable, of, scheduled, Subject, throwError, pipe } from 'rxjs';
 import {
   map,
   mergeMap,
@@ -619,6 +619,30 @@ describe('share', () => {
           expectSubscriptions(source.subscriptions).toBe(sourceSubs);
         });
       });
+
+      it('should be referentially-transparent', () => {
+        rxTest.run(({ cold, expectObservable, expectSubscriptions }) => {
+          const source1 = cold('-1-2-3-4-5-|');
+          const source1Subs = ' ^----------!';
+          const expected1 = '   -1-2-3-4-5-|';
+          const source2 = cold('-6-7-8-9-0-|');
+          const source2Subs = ' ^----------!';
+          const expected2 = '   -6-7-8-9-0-|';
+
+          // Calls to the _operator_ must be referentially-transparent.
+          const partialPipeLine = pipe(share({ resetOnRefCountZero }));
+
+          // The non-referentially-transparent sharing occurs within the _operator function_
+          // returned by the _operator_ and that happens when the complete pipeline is composed.
+          const shared1 = source1.pipe(partialPipeLine);
+          const shared2 = source2.pipe(partialPipeLine);
+
+          expectObservable(shared1).toBe(expected1);
+          expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+          expectObservable(shared2).toBe(expected2);
+          expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+        });
+      });
     });
   }
 

spec/operators/shareReplay-spec.ts

@@ -3,7 +3,7 @@ import { expect } from 'chai';
 import * as sinon from 'sinon';
 import { shareReplay, mergeMapTo, retry, take } from 'rxjs/operators';
 import { TestScheduler } from 'rxjs/testing';
-import { Observable, Operator, Observer, of, from, defer } from 'rxjs';
+import { Observable, Operator, Observer, of, from, defer, pipe } from 'rxjs';
 import { observableMatcher } from '../helpers/observableMatcher';
 
 /** @test {shareReplay} */
@@ -387,4 +387,28 @@ describe('shareReplay', () => {
   } else {
     console.warn(`No support for FinalizationRegistry in Node ${process.version}`);
   }
+
+  it('should be referentially-transparent', () => {
+    testScheduler.run(({ cold, expectObservable, expectSubscriptions }) => {
+      const source1 = cold('-1-2-3-4-5-|');
+      const source1Subs = ' ^----------!';
+      const expected1 = '   -1-2-3-4-5-|';
+      const source2 = cold('-6-7-8-9-0-|');
+      const source2Subs = ' ^----------!';
+      const expected2 = '   -6-7-8-9-0-|';
+
+      // Calls to the _operator_ must be referentially-transparent.
+      const partialPipeLine = pipe(shareReplay({ refCount: false }));
+
+      // The non-referentially-transparent sharing occurs within the _operator function_
+      // returned by the _operator_ and that happens when the complete pipeline is composed.
+      const shared1 = source1.pipe(partialPipeLine);
+      const shared2 = source2.pipe(partialPipeLine);
+
+      expectObservable(shared1).toBe(expected1);
+      expectSubscriptions(source1.subscriptions).toBe(source1Subs);
+      expectObservable(shared2).toBe(expected2);
+      expectSubscriptions(source2.subscriptions).toBe(source2Subs);
+    });
+  });
 });

src/internal/operators/publish.ts

@@ -85,5 +85,5 @@ export function publish<T, O extends ObservableInput<any>>(selector: (shared: Ob
  * Details: https://rxjs.dev/deprecations/multicasting
  */
 export function publish<T, R>(selector?: OperatorFunction<T, R>): MonoTypeOperatorFunction<T> | OperatorFunction<T, R> {
-  return selector ? connect(selector) : multicast(new Subject<T>());
+  return selector ? (source) => connect(selector)(source) : (source) => multicast(new Subject<T>())(source);
 }

src/internal/operators/publishBehavior.ts

@@ -18,7 +18,9 @@ import { UnaryFunction } from '../types';
  * Details: https://rxjs.dev/deprecations/multicasting
  */
 export function publishBehavior<T>(initialValue: T): UnaryFunction<Observable<T>, ConnectableObservable<T>> {
-  const subject = new BehaviorSubject<T>(initialValue);
   // Note that this has *never* supported the selector function.
-  return (source) => new ConnectableObservable(source, () => subject);
+  return (source) => {
+    const subject = new BehaviorSubject<T>(initialValue);
+    return new ConnectableObservable(source, () => subject);
+  };
 }

src/internal/operators/publishLast.ts

@@ -67,7 +67,9 @@ import { UnaryFunction } from '../types';
  * Details: https://rxjs.dev/deprecations/multicasting
  */
 export function publishLast<T>(): UnaryFunction<Observable<T>, ConnectableObservable<T>> {
-  const subject = new AsyncSubject<T>();
   // Note that this has *never* supported a selector function like `publish` and `publishReplay`.
-  return (source) => new ConnectableObservable(source, () => subject);
+  return (source) => {
+    const subject = new AsyncSubject<T>();
+    return new ConnectableObservable(source, () => subject);
+  };
 }

src/internal/operators/publishReplay.ts

@@ -89,11 +89,8 @@ export function publishReplay<T, R>(
   if (selectorOrScheduler && !isFunction(selectorOrScheduler)) {
     timestampProvider = selectorOrScheduler;
   }
-
   const selector = isFunction(selectorOrScheduler) ? selectorOrScheduler : undefined;
-  const subject = new ReplaySubject<T>(bufferSize, windowTime, timestampProvider);
-
   // Note, we're passing `selector!` here, because at runtime, `undefined` is an acceptable argument
   // but it makes our TypeScript signature for `multicast` unhappy (as it should, because it's gross).
-  return (source: Observable<T>) => multicast(subject, selector!)(source);
+  return (source: Observable<T>) => multicast(new ReplaySubject<T>(bufferSize, windowTime, timestampProvider), selector!)(source);
 }