From c9b5f2b02262b3c1049e3010a3c587368402bed5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Sat, 4 Feb 2023 01:32:22 +0100
Subject: [PATCH] Replace `missingType` with `undefinedType` in the
 `IndexedAccessTypeNode`'s type (#52016)

---
 src/compiler/checker.ts                       |  4 +--
 ...icateAcceptingPartialOfRefinedType.symbols | 26 +++++++++++++++++++
 ...edicateAcceptingPartialOfRefinedType.types | 17 ++++++++++++
 ...ePredicateAcceptingPartialOfRefinedType.ts | 15 +++++++++++
 4 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.symbols
 create mode 100644 tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.types
 create mode 100644 tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6e3448ba929..b1d258e6c2a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17060,8 +17060,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     }
                 }
                 const propType = getTypeOfSymbol(prop);
-                return accessExpression && getAssignmentTargetKind(accessExpression) !== AssignmentKind.Definite ?
-                    getFlowTypeOfReference(accessExpression, propType) :
+                return accessExpression && getAssignmentTargetKind(accessExpression) !== AssignmentKind.Definite ? getFlowTypeOfReference(accessExpression, propType) :
+                    accessNode && isIndexedAccessTypeNode(accessNode) && containsMissingType(propType) ? getUnionType([propType, undefinedType]) :
                     propType;
             }
             if (everyType(objectType, isTupleType) && isNumericLiteralName(propName)) {
diff --git a/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.symbols b/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.symbols
new file mode 100644
index 00000000000..6df3a454fb2
--- /dev/null
+++ b/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.symbols
@@ -0,0 +1,26 @@
+=== tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts ===
+// repro #51953
+
+interface Test {
+>Test : Symbol(Test, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 0, 0))
+
+  testy?: string;
+>testy : Symbol(Test.testy, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 2, 16))
+}
+
+interface Options {
+>Options : Symbol(Options, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 4, 1))
+
+  test: Test['testy'];
+>test : Symbol(Options.test, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 6, 19))
+>Test : Symbol(Test, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 0, 0))
+}
+
+declare function includesAllRequiredOptions(options: Partial<Options>): options is Options;
+>includesAllRequiredOptions : Symbol(includesAllRequiredOptions, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 8, 1))
+>options : Symbol(options, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 10, 44))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Options : Symbol(Options, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 4, 1))
+>options : Symbol(options, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 10, 44))
+>Options : Symbol(Options, Decl(typePredicateAcceptingPartialOfRefinedType.ts, 4, 1))
+
diff --git a/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.types b/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.types
new file mode 100644
index 00000000000..b0605fa5351
--- /dev/null
+++ b/tests/baselines/reference/typePredicateAcceptingPartialOfRefinedType.types
@@ -0,0 +1,17 @@
+=== tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts ===
+// repro #51953
+
+interface Test {
+  testy?: string;
+>testy : string | undefined
+}
+
+interface Options {
+  test: Test['testy'];
+>test : string | undefined
+}
+
+declare function includesAllRequiredOptions(options: Partial<Options>): options is Options;
+>includesAllRequiredOptions : (options: Partial<Options>) => options is Options
+>options : Partial<Options>
+
diff --git a/tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts b/tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts
new file mode 100644
index 00000000000..f15632e59c9
--- /dev/null
+++ b/tests/cases/compiler/typePredicateAcceptingPartialOfRefinedType.ts
@@ -0,0 +1,15 @@
+// @strict: true
+// @exactOptionalPropertyTypes: true
+// @noEmit: true
+
+// repro #51953
+
+interface Test {
+  testy?: string;
+}
+
+interface Options {
+  test: Test['testy'];
+}
+
+declare function includesAllRequiredOptions(options: Partial<Options>): options is Options;