From b8b0d26cb9b9b0573affc6cb2faaa6227db9f49b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Tue, 15 Aug 2023 21:01:21 +0200
Subject: [PATCH] Display write type for property accesses in write locations
 (#54777)

---
 src/compiler/checker.ts                               |  8 ++++++--
 .../quickInfoOnPropertyAccessInWriteLocation1.ts      |  8 ++++++++
 .../quickInfoOnPropertyAccessInWriteLocation2.ts      |  8 ++++++++
 .../quickInfoOnPropertyAccessInWriteLocation3.ts      |  8 ++++++++
 .../quickInfoOnPropertyAccessInWriteLocation4.ts      | 11 +++++++++++
 .../quickInfoOnPropertyAccessInWriteLocation5.ts      | 11 +++++++++++
 6 files changed, 52 insertions(+), 2 deletions(-)
 create mode 100644 tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation1.ts
 create mode 100644 tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation2.ts
 create mode 100644 tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation3.ts
 create mode 100644 tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation4.ts
 create mode 100644 tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation5.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 51cee644b17..06c2808a393 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11541,7 +11541,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     getWriteTypeOfSymbolWithDeferredType(symbol) || getTypeOfSymbolWithDeferredType(symbol) :
                     // NOTE: cast to TransientSymbol should be safe because only TransientSymbols can have CheckFlags.SyntheticProperty
                     (symbol as TransientSymbol).links.writeType || (symbol as TransientSymbol).links.type! :
-                getTypeOfSymbol(symbol);
+                removeMissingType(getTypeOfSymbol(symbol), !!(symbol.flags & SymbolFlags.Optional));
         }
         if (symbol.flags & SymbolFlags.Accessor) {
             return checkFlags & CheckFlags.Instantiated ?
@@ -27703,7 +27703,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 location = location.parent;
             }
             if (isExpressionNode(location) && (!isAssignmentTarget(location) || isWriteAccess(location))) {
-                const type = removeOptionalTypeMarker(getTypeOfExpression(location as Expression));
+                const type = removeOptionalTypeMarker(
+                    isWriteAccess(location) && location.kind === SyntaxKind.PropertyAccessExpression ?
+                        checkPropertyAccessExpression(location as PropertyAccessExpression, /*checkMode*/ undefined, /*writeOnly*/ true) :
+                        getTypeOfExpression(location as Expression)
+                );
                 if (getExportSymbolOfValueSymbolIfExported(getNodeLinks(location).resolvedSymbol) === symbol) {
                     return type;
                 }
diff --git a/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation1.ts b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation1.ts
new file mode 100644
index 00000000000..81299002a12
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation1.ts
@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts'/>
+
+// @strict: true
+// @exactOptionalPropertyTypes: true
+//// declare const xx: { prop?: number };
+//// xx.prop/*1*/ = 1;
+
+verify.quickInfoAt('1', '(property) prop?: number');
diff --git a/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation2.ts b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation2.ts
new file mode 100644
index 00000000000..02babc99c22
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation2.ts
@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts'/>
+
+// @strict: true
+// @exactOptionalPropertyTypes: true
+//// declare const xx: { prop?: number };
+//// xx.prop/*1*/ += 1;
+
+verify.quickInfoAt('1', '(property) prop?: number');
diff --git a/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation3.ts b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation3.ts
new file mode 100644
index 00000000000..6b2e7092c33
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation3.ts
@@ -0,0 +1,8 @@
+/// <reference path='fourslash.ts'/>
+
+// @strict: true
+// @exactOptionalPropertyTypes: true
+//// declare const xx: { prop?: number };
+//// xx.prop/*1*/ ??= 1;
+
+verify.quickInfoAt('1', '(property) prop?: number');
diff --git a/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation4.ts b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation4.ts
new file mode 100644
index 00000000000..acf55817c39
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation4.ts
@@ -0,0 +1,11 @@
+/// <reference path='fourslash.ts'/>
+
+// @strict: true
+//// interface Serializer {
+////   set value(v: string | number | boolean);
+////   get value(): string;
+//// }
+//// declare let box: Serializer;
+//// box.value/*1*/ = true;
+
+verify.quickInfoAt('1', '(property) Serializer.value: string | number | boolean');
diff --git a/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation5.ts b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation5.ts
new file mode 100644
index 00000000000..06ea4ba9166
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoOnPropertyAccessInWriteLocation5.ts
@@ -0,0 +1,11 @@
+/// <reference path='fourslash.ts'/>
+
+// @strict: true
+//// interface Serializer {
+////   set value(v: string | number);
+////   get value(): string;
+//// }
+//// declare let box: Serializer;
+//// box.value/*1*/ += 10;
+
+verify.quickInfoAt('1', '(property) Serializer.value: string | number');