fix(toObservableValue): accommodate all observable inputs (#2471)

- Switches toObservableValue to just use rxjs `from`. This will ensure it works with all
  types that `rxjs` is compatable with. Also, the checks in `toObservableValue` were redundant if
  `from` was used.  For example, if `x` is `Observable` from rxjs, then `from(x) === x` would be `true`.
  `from` does all of the necessary checks. Also, `from` will do the work of figuring out of it happens
  to be an observable that has interop with RxJS, or is an observable from another instance
  of rxjs (in node_modules, Node scenario).
- Also `x == null` will only return `true` if `x` is `undefined` or `null`.
- Fixes the return types of `toObservableValue` to be more true to form. If you return
  `Observable<X> | Observable<Y> | Observable<Z>`, it's really no different than `Observable<X | Y | Z>`,
  because there's no static/synchronous way to narrow the type of the `Observable` to say, `Observable<X>`
  in either scenario.
- Removes unecessary types in favor of more obvious explicit types
- Removes superfluous isObservable-type assert function
- Removes unused assertion methods. Not sure what those were used for, as they were exported, but two
  were ill-advised, as they were doing type-narrowing by iterating over an array, making it an O(n) operation
  just to narrow a type.

Author: benlesh

modules/component/spec/core/projections/toObservableValue.spec.ts

@@ -1,8 +1,11 @@
-import { EMPTY, isObservable, Observable, of } from 'rxjs';
+import { EMPTY, isObservable, Observable } from 'rxjs';
 import { toObservableValue } from '../../../src/core/projections';
 
 describe('toObservableValue', () => {
   describe('used as RxJS creation function', () => {
+    // NOTE: (benlesh) These tests are probably all redundant, as you're just
+    // testing `rxjs` from in every case but `null` and `undefined`.
+
     it('should take observables', () => {
       const observable: Observable<any> = toObservableValue(EMPTY);
       expect(isObservable(observable)).toBe(true);
@@ -15,6 +18,12 @@ describe('toObservableValue', () => {
       expect(isObservable(observable)).toBe(true);
     });
 
+    it('should take an iterable', () => {
+      const set = new Set([1, 2, 3]);
+      const observable: Observable<any> = toObservableValue(set.values());
+      expect(isObservable(observable)).toBe(true);
+    });
+
     it('should take undefined', () => {
       const observable: Observable<any> = toObservableValue(undefined);
       expect(isObservable(observable)).toBe(true);
@@ -25,7 +34,9 @@ describe('toObservableValue', () => {
       expect(isObservable(observable)).toBe(true);
     });
 
-    it('throw if no observable, promise, undefined or null is passed', () => {
+    // NOTE: (benlesh) - AFIACT this test would never have passed with the existing code
+    // `toObservableValue(null)` was made to return `of(null)`
+    xit('throw if no observable, promise, undefined or null is passed', () => {
       const observable: Observable<any> = toObservableValue(null);
       observable.subscribe({
         error(e) {

modules/component/src/core/cd-aware.abstract.ts

@@ -61,7 +61,7 @@ export function createCdAware<U>(cfg: {
     // Ignore potential observables of the same instances
     distinctUntilChanged(),
     // Try to convert it to values, throw if not possible
-    map(v => toObservableValue(v)),
+    map(toObservableValue),
     tap((v: any) => {
       cfg.resetContextObserver.next(v);
       cfg.work();

modules/component/src/core/projections/toObservableValue.ts

@@ -1,32 +1,7 @@
-import { from, of } from 'rxjs';
-import {
-  isObservableGuard,
-  isPromiseGuard,
-  PotentialObservableValue,
-  Output,
-} from '../utils';
+import { from, of, Observable, ObservableInput } from 'rxjs';
 
 export function toObservableValue<T>(
-  p: PotentialObservableValue<T>
-): Output<T> {
-  // Comparing to the literal null value with the == operator covers both null and undefined values.
-  if (p === null) {
-    return of(p);
-  }
-
-  if (p === undefined) {
-    return of(p);
-  }
-
-  if (isObservableGuard<T>(p)) {
-    return p;
-  }
-
-  if (isPromiseGuard<T>(p)) {
-    return from(p);
-  }
-
-  throw new Error(
-    'Argument not observable. Only null/undefined or Promise/Observable-like values are allowed.'
-  );
+  p: ObservableInput<T> | undefined | null
+): Observable<T | undefined | null> {
+  return p == null ? of(p) : from(p);
 }

modules/component/src/core/utils/index.ts

@@ -2,14 +2,3 @@ export { getChangeDetectionHandler } from './get-change-detection-handling';
 export { getGlobalThis } from './get-global-this';
 export { isIvy } from './is-ivy';
 export { hasZone } from './has-zone';
-
-export {
-  isDefinedGuard,
-  isIterableGuard,
-  isObservableGuard,
-  isOperateFnArrayGuard,
-  isPromiseGuard,
-  isStringArrayGuard,
-  PotentialObservableValue,
-  Output,
-} from './typing';