From 55d6e330a1676c01f4ce15434162c1d1aea6060f Mon Sep 17 00:00:00 2001
From: pgorostiagab <pgorostiagab@bloomberg.net>
Date: Thu, 16 Jun 2022 13:16:11 +0100
Subject: [PATCH] Initial hacky implementation using InKeyword narrowing and
 simple test

---
 src/compiler/checker.ts                                  | 8 ++++++++
 tests/cases/compiler/objectHasOwnNarrowingSimpleUnion.ts | 6 ++++++
 2 files changed, 14 insertions(+)
 create mode 100644 tests/cases/compiler/objectHasOwnNarrowingSimpleUnion.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9e56c58411930..d91e4a94bb766 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -25289,6 +25289,7 @@ namespace ts {
             }
 
             function narrowTypeByCallExpression(type: Type, callExpression: CallExpression, assumeTrue: boolean): Type {
+                debugger;
                 if (hasMatchingArgument(callExpression, reference)) {
                     const signature = assumeTrue || !isCallChain(callExpression) ? getEffectsSignature(callExpression) : undefined;
                     const predicate = signature && getTypePredicateOfSignature(signature);
@@ -25306,6 +25307,13 @@ namespace ts {
                         }
                     }
                 }
+
+                if (isPropertyAccessExpression(callExpression.expression)) {
+                    const callAccess = callExpression.expression;
+                    if (isIdentifier(callAccess.name) && callAccess.name.escapedText === "hasOwn" && callExpression.arguments.length === 2 && isStringLiteralLike(callExpression.arguments[1])) {
+                        return narrowByInKeyword(type, callExpression.arguments[1].text as __String, assumeTrue);
+                    }
+                }
                 return type;
             }
 
diff --git a/tests/cases/compiler/objectHasOwnNarrowingSimpleUnion.ts b/tests/cases/compiler/objectHasOwnNarrowingSimpleUnion.ts
new file mode 100644
index 0000000000000..6a5a4acecc1ff
--- /dev/null
+++ b/tests/cases/compiler/objectHasOwnNarrowingSimpleUnion.ts
@@ -0,0 +1,6 @@
+// @target: es2022
+
+declare const abcd: { a: string, b: number } | { c: number, d: string };
+if (Object.hasOwn(abcd, "a")) {
+  abcd.b;
+}