fix: Account for subscriber chaining.

Author: cartant

source/rules/rxjsNoIgnoredSubscriptionRule.ts

@@ -46,6 +46,15 @@ export class Rule extends Lint.Rules.TypedRule {
           propertyAccessExpression.expression
         );
         if (couldBeType(type, "Observable")) {
+          if (
+            callExpression.arguments.length === 1 &&
+            couldBeType(
+              typeChecker.getTypeAtLocation(callExpression.arguments[0]),
+              "Subscriber"
+            )
+          ) {
+            return;
+          }
           const { name } = callExpression.expression;
           failures.push(
             new Lint.RuleFailure(

test/v6/fixtures/no-ignored-subscription/default/fixture.ts.lint

@@ -1,4 +1,4 @@
-import { of, Subscription } from "rxjs";
+import { of, Subscriber, Subscription } from "rxjs";
 
 of(42).subscribe();
        ~~~~~~~~~                            [no-ignored-subscription]
@@ -9,4 +9,7 @@ b = of(42).subscribe();
 const c = [of(42).subscribe()];
 const d = { subscription: of(42).subscribe() };
 
+const subscriber = new Subscriber<number>();
+of(42).subscribe(subscriber);
+
 [no-ignored-subscription]: Ignoring returned subscriptions is forbidden