From 228b727ff16d33dc4925e6414655652a3832ef33 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 4 Sep 2019 16:49:59 -0700
Subject: [PATCH] Add regression test

---
 .../compiler/observableInferenceCanBeMade.ts  | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 tests/cases/compiler/observableInferenceCanBeMade.ts

diff --git a/tests/cases/compiler/observableInferenceCanBeMade.ts b/tests/cases/compiler/observableInferenceCanBeMade.ts
new file mode 100644
index 00000000000..72685daabf6
--- /dev/null
+++ b/tests/cases/compiler/observableInferenceCanBeMade.ts
@@ -0,0 +1,22 @@
+// @strict: true
+
+// Repro from #33131
+
+declare function of<T>(a: T): Observable<T>;
+declare function from<O extends ObservableInput<any>>(input: O): Observable<ObservedValueOf<O>>;
+
+type ObservedValueOf<O> = O extends ObservableInput<infer T> ? T : never;
+
+interface Subscribable<T> {
+    subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): void;
+}
+type ObservableInput<T> = Subscribable<T> | Subscribable<never>;
+
+
+declare class Observable<T> implements Subscribable<T> {
+    subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): void;
+}
+
+function asObservable(input: string | ObservableInput<string>): Observable<string> {
+    return typeof input === 'string' ? of(input) : from(input)
+}