From f29d7df5d150070eb0e3e4cf49d76560d72ea63b Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 24 May 2017 15:50:30 -0700
Subject: [PATCH] Add tests

---
 .../inferFromGenericFunctionReturnTypes1.ts   | 70 ++++++++++++++
 .../inferFromGenericFunctionReturnTypes2.ts   | 94 +++++++++++++++++++
 2 files changed, 164 insertions(+)
 create mode 100644 tests/cases/compiler/inferFromGenericFunctionReturnTypes1.ts
 create mode 100644 tests/cases/compiler/inferFromGenericFunctionReturnTypes2.ts

diff --git a/tests/cases/compiler/inferFromGenericFunctionReturnTypes1.ts b/tests/cases/compiler/inferFromGenericFunctionReturnTypes1.ts
new file mode 100644
index 00000000000..3fb454ec7e5
--- /dev/null
+++ b/tests/cases/compiler/inferFromGenericFunctionReturnTypes1.ts
@@ -0,0 +1,70 @@
+// Repro from #15680
+
+// This is a contrived class. We could do the same thing with Observables, etc.
+class SetOf<A> {
+  _store: A[];
+
+  add(a: A) {
+    this._store.push(a);
+  }
+
+  transform<B>(transformer: (a: SetOf<A>) => SetOf<B>): SetOf<B> {
+    return transformer(this);
+  }
+
+  forEach(fn: (a: A, index: number) => void) {
+      this._store.forEach((a, i) => fn(a, i));
+  }
+}
+
+function compose<A, B, C, D, E>(
+  fnA: (a: SetOf<A>) => SetOf<B>, 
+  fnB: (b: SetOf<B>) => SetOf<C>, 
+  fnC: (c: SetOf<C>) => SetOf<D>,
+  fnD: (c: SetOf<D>) => SetOf<E>,
+):(x: SetOf<A>) => SetOf<E>;
+/* ... etc ... */
+function compose<T>(...fns: ((x: T) => T)[]): (x: T) => T {
+  return (x: T) => fns.reduce((prev, fn) => fn(prev), x);
+}
+
+function map<A, B>(fn: (a: A) => B): (s: SetOf<A>) => SetOf<B> {
+  return (a: SetOf<A>) => {
+    const b: SetOf<B> = new SetOf();
+    a.forEach(x => b.add(fn(x)));
+    return b;
+  }
+}
+
+function filter<A>(predicate: (a: A) => boolean): (s: SetOf<A>) => SetOf<A> {
+  return (a: SetOf<A>) => {
+    const result = new SetOf<A>();
+    a.forEach(x => {
+      if (predicate(x)) result.add(x);
+    });
+   return result;
+  }
+}
+
+const testSet = new SetOf<number>();
+testSet.add(1);
+testSet.add(2);
+testSet.add(3);
+
+testSet.transform(
+  compose(
+    filter(x => x % 1 === 0),
+    map(x => x + x),
+    map(x => x + '!!!'),
+    map(x => x.toUpperCase())
+  )
+)
+
+testSet.transform(
+  compose(
+    filter(x => x % 1 === 0),
+    map(x => x + x),
+    map(x => 123),  // Whoops a bug
+    map(x => x.toUpperCase()) // causes an error!
+  )
+)
diff --git a/tests/cases/compiler/inferFromGenericFunctionReturnTypes2.ts b/tests/cases/compiler/inferFromGenericFunctionReturnTypes2.ts
new file mode 100644
index 00000000000..314159d363c
--- /dev/null
+++ b/tests/cases/compiler/inferFromGenericFunctionReturnTypes2.ts
@@ -0,0 +1,94 @@
+type Mapper<T, U> = (x: T) => U;
+
+declare function wrap<T, U>(cb: Mapper<T, U>): Mapper<T, U>;
+
+declare function arrayize<T, U>(cb: Mapper<T, U>): Mapper<T, U[]>;
+
+declare function combine<A, B, C>(f: (x: A) => B, g: (x: B) => C): (x: A) => C;
+
+declare function foo(f: Mapper<string, number>): void;
+
+let f1: Mapper<string, number> = s => s.length;
+let f2: Mapper<string, number> = wrap(s => s.length);
+let f3: Mapper<string, number[]> = arrayize(wrap(s => s.length));
+let f4: Mapper<string, boolean> = combine(wrap(s => s.length), wrap(n => n >= 10));
+
+foo(wrap(s => s.length));
+
+let a1 = ["a", "b"].map(s => s.length);
+let a2 = ["a", "b"].map(wrap(s => s.length));
+let a3 = ["a", "b"].map(wrap(arrayize(s => s.length)));
+let a4 = ["a", "b"].map(combine(wrap(s => s.length), wrap(n => n > 10)));
+let a5 = ["a", "b"].map(combine(identity, wrap(s => s.length)));
+let a6 = ["a", "b"].map(combine(wrap(s => s.length), identity));
+
+// This is a contrived class. We could do the same thing with Observables, etc.
+class SetOf<A> {
+  _store: A[];
+
+  add(a: A) {
+    this._store.push(a);
+  }
+
+  transform<B>(transformer: (a: SetOf<A>) => SetOf<B>): SetOf<B> {
+    return transformer(this);
+  }
+
+  forEach(fn: (a: A, index: number) => void) {
+      this._store.forEach((a, i) => fn(a, i));
+  }
+}
+
+function compose<A, B, C, D, E>(
+  fnA: (a: SetOf<A>) => SetOf<B>, 
+  fnB: (b: SetOf<B>) => SetOf<C>, 
+  fnC: (c: SetOf<C>) => SetOf<D>,
+  fnD: (c: SetOf<D>) => SetOf<E>,
+):(x: SetOf<A>) => SetOf<E>;
+/* ... etc ... */
+function compose<T>(...fns: ((x: T) => T)[]): (x: T) => T {
+  return (x: T) => fns.reduce((prev, fn) => fn(prev), x);
+}
+
+function map<A, B>(fn: (a: A) => B): (s: SetOf<A>) => SetOf<B> {
+  return (a: SetOf<A>) => {
+    const b: SetOf<B> = new SetOf();
+    a.forEach(x => b.add(fn(x)));
+    return b;
+  }
+}
+
+function filter<A>(predicate: (a: A) => boolean): (s: SetOf<A>) => SetOf<A> {
+  return (a: SetOf<A>) => {
+    const result = new SetOf<A>();
+    a.forEach(x => {
+      if (predicate(x)) result.add(x);
+    });
+   return result;
+  }
+}
+
+const testSet = new SetOf<number>();
+testSet.add(1);
+testSet.add(2);
+testSet.add(3);
+
+const t1 = testSet.transform(
+  compose(
+    filter(x => x % 1 === 0),
+    map(x => x + x),
+    map(x => x + '!!!'),
+    map(x => x.toUpperCase())
+  )
+)
+
+declare function identity<T>(x: T): T;
+
+const t2 = testSet.transform(
+  compose(
+    filter(x => x % 1 === 0),
+    identity,
+    map(x => x + '!!!'),
+    map(x => x.toUpperCase())
+  )
+)