From f8aaccdd1d64dca3e3d99a02643264b9f17a05e7 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 5 Jun 2019 16:55:08 -0700
Subject: [PATCH] Add tests

---
 tests/cases/compiler/numericEnumMappedType.ts | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 tests/cases/compiler/numericEnumMappedType.ts

diff --git a/tests/cases/compiler/numericEnumMappedType.ts b/tests/cases/compiler/numericEnumMappedType.ts
new file mode 100644
index 00000000000..be29167bb3d
--- /dev/null
+++ b/tests/cases/compiler/numericEnumMappedType.ts
@@ -0,0 +1,38 @@
+// @strict: true
+
+// Repro from #31771
+
+enum E1 { ONE, TWO, THREE }
+declare enum E2 { ONE, TWO, THREE }
+
+type Bins1 = { [k in E1]?: string; }
+type Bins2 = { [k in E2]?: string; }
+
+const b1: Bins1 = {};
+const b2: Bins2 = {};
+
+const e1: E1 = E1.ONE;
+const e2: E2 = E2.ONE;
+
+b1[1] = "a";
+b1[e1] = "b";
+
+b2[1] = "a";
+b2[e2] = "b";
+
+// Multiple numeric enum types accrue to the same numeric index signature in a mapped type
+
+declare function val(): number;
+
+enum N1 { A = val(), B = val() }
+enum N2 { C = val(), D = val() }
+
+type T1 = { [K in N1 | N2]: K };
+
+// Enum types with string valued members are always literal enum types and therefore
+// ONE and TWO below are not computed members but rather just numerically valued members
+// with auto-incremented values.
+
+declare enum E { ONE, TWO, THREE = 'x' }
+const e: E = E.ONE;
+const x: E.ONE = e;