From e3d6189e3ab054a11ae5be246d9dcc1cf245fd3b Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <DanielRosenwasser@users.noreply.github.com>
Date: Thu, 1 Jul 2021 15:19:11 -0700
Subject: [PATCH] Correctly check for 'delete' on optional properties in
 'exactOptionalPropertyTypes'. (#44854)

* Check for optionality in 'delete'.

* Accepted baselines.
---
 src/compiler/checker.ts                                   | 8 ++++----
 ...pertyTypes(exactoptionalpropertytypes=true).errors.txt | 8 +-------
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f0f817facfc..761ca7a95ec 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -31402,16 +31402,16 @@ namespace ts {
                 if (isReadonlySymbol(symbol)) {
                     error(expr, Diagnostics.The_operand_of_a_delete_operator_cannot_be_a_read_only_property);
                 }
-
-                checkDeleteExpressionMustBeOptional(expr, getTypeOfSymbol(symbol));
+                checkDeleteExpressionMustBeOptional(expr, symbol);
             }
             return booleanType;
         }
 
-        function checkDeleteExpressionMustBeOptional(expr: AccessExpression, type: Type) {
+        function checkDeleteExpressionMustBeOptional(expr: AccessExpression, symbol: Symbol) {
+            const type = getTypeOfSymbol(symbol);
             if (strictNullChecks &&
                 !(type.flags & (TypeFlags.AnyOrUnknown | TypeFlags.Never)) &&
-                !(exactOptionalPropertyTypes ? 0 : getFalsyFlags(type) & TypeFlags.Undefined)) {
+                !(exactOptionalPropertyTypes ? hasQuestionToken(symbol.valueDeclaration!) : getFalsyFlags(type) & TypeFlags.Undefined)) {
                 error(expr, Diagnostics.The_operand_of_a_delete_operator_must_be_optional);
             }
         }
diff --git a/tests/baselines/reference/deleteExpressionMustBeOptional_exactOptionalPropertyTypes(exactoptionalpropertytypes=true).errors.txt b/tests/baselines/reference/deleteExpressionMustBeOptional_exactOptionalPropertyTypes(exactoptionalpropertytypes=true).errors.txt
index 300d2370355..03d5b58f2e7 100644
--- a/tests/baselines/reference/deleteExpressionMustBeOptional_exactOptionalPropertyTypes(exactoptionalpropertytypes=true).errors.txt
+++ b/tests/baselines/reference/deleteExpressionMustBeOptional_exactOptionalPropertyTypes(exactoptionalpropertytypes=true).errors.txt
@@ -1,13 +1,11 @@
 tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(25,8): error TS2790: The operand of a 'delete' operator must be optional.
 tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(26,8): error TS2790: The operand of a 'delete' operator must be optional.
 tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(27,8): error TS2790: The operand of a 'delete' operator must be optional.
-tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(28,8): error TS2790: The operand of a 'delete' operator must be optional.
 tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(29,8): error TS2790: The operand of a 'delete' operator must be optional.
-tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(30,8): error TS2790: The operand of a 'delete' operator must be optional.
 tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts(34,10): error TS2339: Property 'j' does not exist on type 'Foo'.
 
 
-==== tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts (7 errors) ====
+==== tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.ts (5 errors) ====
     interface Foo {
         a: number
         b: number | undefined
@@ -42,14 +40,10 @@ tests/cases/compiler/deleteExpressionMustBeOptional_exactOptionalPropertyTypes.t
            ~~~
 !!! error TS2790: The operand of a 'delete' operator must be optional.
     delete f.d
-           ~~~
-!!! error TS2790: The operand of a 'delete' operator must be optional.
     delete f.e
            ~~~
 !!! error TS2790: The operand of a 'delete' operator must be optional.
     delete f.f
-           ~~~
-!!! error TS2790: The operand of a 'delete' operator must be optional.
     delete f.g
     delete f.h
     delete f.i