assume that all pipe elements that return something, return outputs

javascript/ql/src/semmle/javascript/frameworks/RxJS.qll

@@ -34,7 +34,8 @@ private DataFlow::Node pipeInput(DataFlow::CallNode pipe) {
  * the pipe.
  */
 private DataFlow::Node pipeOutput(DataFlow::CallNode pipe) {
-  pipe = DataFlow::moduleMember("rxjs/operators", "map").getACall() and
+  // we assume if there is a return, it is an output.
+  pipe = DataFlow::moduleMember("rxjs/operators", _).getACall() and
   result = pipe.getCallback(0).getReturnNode()
   or
   pipe = DataFlow::moduleMember("rxjs/operators", "filter").getACall() and

javascript/ql/test/library-tests/TaintTracking/BasicTaintTracking.expected

@@ -112,6 +112,8 @@ typeInferenceMismatch
 | rxjs.js:13:1:13:8 | source() | rxjs.js:17:23:17:23 | x |
 | rxjs.js:13:1:13:8 | source() | rxjs.js:18:23:18:23 | x |
 | rxjs.js:13:1:13:8 | source() | rxjs.js:22:14:22:17 | data |
+| rxjs.js:27:24:27:32 | source(x) | rxjs.js:29:23:29:23 | x |
+| rxjs.js:27:24:27:32 | source(x) | rxjs.js:34:14:34:17 | data |
 | sanitizer-function.js:12:17:12:24 | source() | sanitizer-function.js:14:10:14:14 | taint |
 | sanitizer-function.js:12:17:12:24 | source() | sanitizer-function.js:33:14:33:18 | taint |
 | sanitizer-guards.js:2:11:2:18 | source() | sanitizer-guards.js:4:8:4:8 | x |

javascript/ql/test/library-tests/TaintTracking/rxjs.js

@@ -1,4 +1,4 @@
-import { map, tap, catchError } from 'rxjs/operators';
+import { map, tap, catchError, switchMap, filter } from 'rxjs/operators';
 
 source()
     .pipe(
@@ -21,3 +21,15 @@ source()
     .subscribe(data => {
         sink(data)
     });
+
+myIdentifier()
+    .pipe(
+        switchMap(x => source(x)),
+        filter(x => myFilter(x)),
+        tap(x => sink(x)),
+        catchError(err => {}),
+        map(x => x + 'foo')
+    )
+    .subscribe(data => {
+        sink(data)
+    });