Add regression test

Author: ahejlsberg

tests/baselines/reference/emptyObjectNarrowing.js

@@ -0,0 +1,22 @@
+//// [emptyObjectNarrowing.ts]
+// Repro from #49988
+
+declare function isObject(value: unknown): value is Record<string, unknown>;
+const obj = {};
+if (isObject(obj)) {
+    obj['attr'];
+}
+
+
+//// [emptyObjectNarrowing.js]
+"use strict";
+// Repro from #49988
+var obj = {};
+if (isObject(obj)) {
+    obj['attr'];
+}
+
+
+//// [emptyObjectNarrowing.d.ts]
+declare function isObject(value: unknown): value is Record<string, unknown>;
+declare const obj: {};

tests/baselines/reference/emptyObjectNarrowing.symbols

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/emptyObjectNarrowing.ts ===
+// Repro from #49988
+
+declare function isObject(value: unknown): value is Record<string, unknown>;
+>isObject : Symbol(isObject, Decl(emptyObjectNarrowing.ts, 0, 0))
+>value : Symbol(value, Decl(emptyObjectNarrowing.ts, 2, 26))
+>value : Symbol(value, Decl(emptyObjectNarrowing.ts, 2, 26))
+>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
+
+const obj = {};
+>obj : Symbol(obj, Decl(emptyObjectNarrowing.ts, 3, 5))
+
+if (isObject(obj)) {
+>isObject : Symbol(isObject, Decl(emptyObjectNarrowing.ts, 0, 0))
+>obj : Symbol(obj, Decl(emptyObjectNarrowing.ts, 3, 5))
+
+    obj['attr'];
+>obj : Symbol(obj, Decl(emptyObjectNarrowing.ts, 3, 5))
+}
+

tests/baselines/reference/emptyObjectNarrowing.types

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/emptyObjectNarrowing.ts ===
+// Repro from #49988
+
+declare function isObject(value: unknown): value is Record<string, unknown>;
+>isObject : (value: unknown) => value is Record<string, unknown>
+>value : unknown
+
+const obj = {};
+>obj : {}
+>{} : {}
+
+if (isObject(obj)) {
+>isObject(obj) : boolean
+>isObject : (value: unknown) => value is Record<string, unknown>
+>obj : {}
+
+    obj['attr'];
+>obj['attr'] : unknown
+>obj : Record<string, unknown>
+>'attr' : "attr"
+}
+

tests/cases/compiler/emptyObjectNarrowing.ts

@@ -0,0 +1,10 @@
+// @strict: true
+// @declaration: true
+
+// Repro from #49988
+
+declare function isObject(value: unknown): value is Record<string, unknown>;
+const obj = {};
+if (isObject(obj)) {
+    obj['attr'];
+}