From 0a1f3b64fbadfced18021052112e9f3579d3525a Mon Sep 17 00:00:00 2001
From: aleph-naught2tog <maggie@8thlight.com>
Date: Wed, 14 Nov 2018 00:30:54 -0600
Subject: [PATCH] Disallows `async abstract` method declarations

Since we do not allow `async` as a modifier on type members such as in an interface, it was decided that it should also not be allowed on abstract methods.

Fixes #28516.
---
 src/compiler/checker.ts                            |  3 +++
 tests/baselines/reference/abstractAsync.errors.txt |  9 +++++++++
 tests/baselines/reference/abstractAsync.js         | 11 +++++++++++
 tests/baselines/reference/abstractAsync.symbols    |  8 ++++++++
 tests/baselines/reference/abstractAsync.types      |  8 ++++++++
 tests/cases/compiler/abstractAsync.ts              |  4 ++++
 6 files changed, 43 insertions(+)
 create mode 100644 tests/baselines/reference/abstractAsync.errors.txt
 create mode 100644 tests/baselines/reference/abstractAsync.js
 create mode 100644 tests/baselines/reference/abstractAsync.symbols
 create mode 100644 tests/baselines/reference/abstractAsync.types
 create mode 100644 tests/cases/compiler/abstractAsync.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index e59641bed412e..54d6daca678a3 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -28342,6 +28342,9 @@ namespace ts {
                             if (flags & ModifierFlags.Private) {
                                 return grammarErrorOnNode(modifier, Diagnostics._0_modifier_cannot_be_used_with_1_modifier, "private", "abstract");
                             }
+                            if (flags & ModifierFlags.Async) {
+                                return grammarErrorOnNode(modifier, Diagnostics._0_modifier_cannot_be_used_with_1_modifier, "async", "abstract");
+                            }
                         }
 
                         flags |= ModifierFlags.Abstract;
diff --git a/tests/baselines/reference/abstractAsync.errors.txt b/tests/baselines/reference/abstractAsync.errors.txt
new file mode 100644
index 0000000000000..d0f741468b28b
--- /dev/null
+++ b/tests/baselines/reference/abstractAsync.errors.txt
@@ -0,0 +1,9 @@
+tests/cases/compiler/abstractAsync.ts(2,9): error TS1243: 'async' modifier cannot be used with 'abstract' modifier.
+
+
+==== tests/cases/compiler/abstractAsync.ts (1 errors) ====
+    abstract class ShouldFailClass {
+      async abstract badMethod(): Promise<number>;
+            ~~~~~~~~
+!!! error TS1243: 'async' modifier cannot be used with 'abstract' modifier.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/abstractAsync.js b/tests/baselines/reference/abstractAsync.js
new file mode 100644
index 0000000000000..96665a0ada194
--- /dev/null
+++ b/tests/baselines/reference/abstractAsync.js
@@ -0,0 +1,11 @@
+//// [abstractAsync.ts]
+abstract class ShouldFailClass {
+  async abstract badMethod(): Promise<number>;
+}
+
+//// [abstractAsync.js]
+var ShouldFailClass = /** @class */ (function () {
+    function ShouldFailClass() {
+    }
+    return ShouldFailClass;
+}());
diff --git a/tests/baselines/reference/abstractAsync.symbols b/tests/baselines/reference/abstractAsync.symbols
new file mode 100644
index 0000000000000..e0cf473f8b8b5
--- /dev/null
+++ b/tests/baselines/reference/abstractAsync.symbols
@@ -0,0 +1,8 @@
+=== tests/cases/compiler/abstractAsync.ts ===
+abstract class ShouldFailClass {
+>ShouldFailClass : Symbol(ShouldFailClass, Decl(abstractAsync.ts, 0, 0))
+
+  async abstract badMethod(): Promise<number>;
+>badMethod : Symbol(ShouldFailClass.badMethod, Decl(abstractAsync.ts, 0, 32))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
+}
diff --git a/tests/baselines/reference/abstractAsync.types b/tests/baselines/reference/abstractAsync.types
new file mode 100644
index 0000000000000..1b1771c2ca753
--- /dev/null
+++ b/tests/baselines/reference/abstractAsync.types
@@ -0,0 +1,8 @@
+=== tests/cases/compiler/abstractAsync.ts ===
+abstract class ShouldFailClass {
+>ShouldFailClass : ShouldFailClass
+
+  async abstract badMethod(): Promise<number>;
+>badMethod : () => Promise<number>
+>Promise : Promise<T>
+}
diff --git a/tests/cases/compiler/abstractAsync.ts b/tests/cases/compiler/abstractAsync.ts
new file mode 100644
index 0000000000000..efd6d979ed16c
--- /dev/null
+++ b/tests/cases/compiler/abstractAsync.ts
@@ -0,0 +1,4 @@
+// @lib: es2015
+abstract class ShouldFailClass {
+  async abstract badMethod(): Promise<number>;
+}
\ No newline at end of file