Revert "Revert "Add check for delete expression must be optional (#37921

)" (#38154)" (#38173)

This reverts commit 1b8c68d.

src/compiler/checker.ts

@@ -27682,12 +27682,23 @@ namespace ts {
             }
             const links = getNodeLinks(expr);
             const symbol = getExportSymbolOfValueSymbolIfExported(links.resolvedSymbol);
-            if (symbol && isReadonlySymbol(symbol)) {
-                error(expr, Diagnostics.The_operand_of_a_delete_operator_cannot_be_a_read_only_property);
+            if (symbol) {
+                if (isReadonlySymbol(symbol)) {
+                    error(expr, Diagnostics.The_operand_of_a_delete_operator_cannot_be_a_read_only_property);
+                }
+
+                checkDeleteExpressionMustBeOptional(expr, getTypeOfSymbol(symbol));
             }
             return booleanType;
         }
 
+        function checkDeleteExpressionMustBeOptional(expr: AccessExpression, type: Type) {
+            const AnyOrUnknownOrNeverFlags = TypeFlags.AnyOrUnknown | TypeFlags.Never;
+            if (strictNullChecks && !(type.flags & AnyOrUnknownOrNeverFlags) && !(getFalsyFlags(type) & TypeFlags.Undefined)) {
+                error(expr, Diagnostics.The_operand_of_a_delete_operator_must_be_optional);
+            }
+        }
+
         function checkTypeOfExpression(node: TypeOfExpression): Type {
             checkExpression(node.expression);
             return typeofType;

src/compiler/diagnosticMessages.json

@@ -2963,6 +2963,10 @@
         "category": "Error",
         "code": 2789
     },
+    "The operand of a 'delete' operator must be optional.": {
+        "category": "Error",
+        "code": 2790
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

tests/baselines/reference/controlFlowDeleteOperator.errors.txt

@@ -1,7 +1,8 @@
+tests/cases/conformance/controlFlow/controlFlowDeleteOperator.ts(10,12): error TS2790: The operand of a 'delete' operator must be optional.
 tests/cases/conformance/controlFlow/controlFlowDeleteOperator.ts(14,12): error TS2703: The operand of a 'delete' operator must be a property reference.
 
 
-==== tests/cases/conformance/controlFlow/controlFlowDeleteOperator.ts (1 errors) ====
+==== tests/cases/conformance/controlFlow/controlFlowDeleteOperator.ts (2 errors) ====
     function f() {
         let x: { a?: number | string, b: number | string } = { b: 1 };
         x.a;
@@ -12,6 +13,8 @@ tests/cases/conformance/controlFlow/controlFlowDeleteOperator.ts(14,12): error T
         x.b;
         delete x.a;
         delete x.b;
+               ~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
         x.a;
         x.b;
         x;

tests/baselines/reference/deleteChain.errors.txt

@@ -0,0 +1,66 @@
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(2,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(3,9): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(6,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(7,9): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(10,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(11,9): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(14,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(15,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(16,9): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(19,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(20,9): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(23,8): error TS2790: The operand of a 'delete' operator must be optional.
+tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts(24,9): error TS2790: The operand of a 'delete' operator must be optional.
+
+
+==== tests/cases/conformance/expressions/optionalChaining/delete/deleteChain.ts (13 errors) ====
+    declare const o1: undefined | { b: string };
+    delete o1?.b;
+           ~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o1?.b);
+            ~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+
+    declare const o2: undefined | { b: { c: string } };
+    delete o2?.b.c;
+           ~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o2?.b.c);
+            ~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+
+    declare const o3: { b: undefined | { c: string } };
+    delete o3.b?.c;
+           ~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o3.b?.c);
+            ~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+
+    declare const o4: { b?: { c: { d?: { e: string } } } };
+    delete o4.b?.c.d?.e;
+           ~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o4.b?.c.d)?.e;
+           ~~~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o4.b?.c.d?.e);
+            ~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+
+    declare const o5: { b?(): { c: { d?: { e: string } } } };
+    delete o5.b?.().c.d?.e;
+           ~~~~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o5.b?.().c.d?.e);
+            ~~~~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+
+    declare const o6: { b?: { c: { d?: { e: string } } } };
+    delete o6.b?.['c'].d?.['e'];
+           ~~~~~~~~~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.
+    delete (o6.b?.['c'].d?.['e']);
+            ~~~~~~~~~~~~~~~~~~~~
+!!! error TS2790: The operand of a 'delete' operator must be optional.

tests/baselines/reference/deleteExpressionMustBeOptional(strict=false).errors.txt

@@ -0,0 +1,46 @@
+tests/cases/compiler/deleteExpressionMustBeOptional.ts(34,10): error TS2339: Property 'j' does not exist on type 'Foo'.
+
+
+==== tests/cases/compiler/deleteExpressionMustBeOptional.ts (1 errors) ====
+    interface Foo {
+        a: number
+        b: number | undefined
+        c: number | null
+        d?: number
+        e: number | undefined | null
+        f?: number | undefined | null
+        g: unknown
+        h: any
+        i: never
+    }
+
+    interface AA {
+        [s: string]: number
+    }
+
+    type BB = {
+        [P in keyof any]: number
+    }
+
+    declare const f: Foo
+    declare const a: AA
+    declare const b: BB
+
+    delete f.a
+    delete f.b
+    delete f.c
+    delete f.d
+    delete f.e
+    delete f.f
+    delete f.g
+    delete f.h
+    delete f.i
+    delete f.j
+             ~
+!!! error TS2339: Property 'j' does not exist on type 'Foo'.
+
+    delete a.a
+    delete a.b
+
+    delete b.a
+    delete b.b

tests/baselines/reference/deleteExpressionMustBeOptional(strict=false).js

@@ -0,0 +1,57 @@
+//// [deleteExpressionMustBeOptional.ts]
+interface Foo {
+    a: number
+    b: number | undefined
+    c: number | null
+    d?: number
+    e: number | undefined | null
+    f?: number | undefined | null
+    g: unknown
+    h: any
+    i: never
+}
+
+interface AA {
+    [s: string]: number
+}
+
+type BB = {
+    [P in keyof any]: number
+}
+
+declare const f: Foo
+declare const a: AA
+declare const b: BB
+
+delete f.a
+delete f.b
+delete f.c
+delete f.d
+delete f.e
+delete f.f
+delete f.g
+delete f.h
+delete f.i
+delete f.j
+
+delete a.a
+delete a.b
+
+delete b.a
+delete b.b
+
+//// [deleteExpressionMustBeOptional.js]
+delete f.a;
+delete f.b;
+delete f.c;
+delete f.d;
+delete f.e;
+delete f.f;
+delete f.g;
+delete f.h;
+delete f.i;
+delete f.j;
+delete a.a;
+delete a.b;
+delete b.a;
+delete b.b;

tests/baselines/reference/deleteExpressionMustBeOptional(strict=false).symbols

@@ -0,0 +1,118 @@
+=== tests/cases/compiler/deleteExpressionMustBeOptional.ts ===
+interface Foo {
+>Foo : Symbol(Foo, Decl(deleteExpressionMustBeOptional.ts, 0, 0))
+
+    a: number
+>a : Symbol(Foo.a, Decl(deleteExpressionMustBeOptional.ts, 0, 15))
+
+    b: number | undefined
+>b : Symbol(Foo.b, Decl(deleteExpressionMustBeOptional.ts, 1, 13))
+
+    c: number | null
+>c : Symbol(Foo.c, Decl(deleteExpressionMustBeOptional.ts, 2, 25))
+
+    d?: number
+>d : Symbol(Foo.d, Decl(deleteExpressionMustBeOptional.ts, 3, 20))
+
+    e: number | undefined | null
+>e : Symbol(Foo.e, Decl(deleteExpressionMustBeOptional.ts, 4, 14))
+
+    f?: number | undefined | null
+>f : Symbol(Foo.f, Decl(deleteExpressionMustBeOptional.ts, 5, 32))
+
+    g: unknown
+>g : Symbol(Foo.g, Decl(deleteExpressionMustBeOptional.ts, 6, 33))
+
+    h: any
+>h : Symbol(Foo.h, Decl(deleteExpressionMustBeOptional.ts, 7, 14))
+
+    i: never
+>i : Symbol(Foo.i, Decl(deleteExpressionMustBeOptional.ts, 8, 10))
+}
+
+interface AA {
+>AA : Symbol(AA, Decl(deleteExpressionMustBeOptional.ts, 10, 1))
+
+    [s: string]: number
+>s : Symbol(s, Decl(deleteExpressionMustBeOptional.ts, 13, 5))
+}
+
+type BB = {
+>BB : Symbol(BB, Decl(deleteExpressionMustBeOptional.ts, 14, 1))
+
+    [P in keyof any]: number
+>P : Symbol(P, Decl(deleteExpressionMustBeOptional.ts, 17, 5))
+}
+
+declare const f: Foo
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>Foo : Symbol(Foo, Decl(deleteExpressionMustBeOptional.ts, 0, 0))
+
+declare const a: AA
+>a : Symbol(a, Decl(deleteExpressionMustBeOptional.ts, 21, 13))
+>AA : Symbol(AA, Decl(deleteExpressionMustBeOptional.ts, 10, 1))
+
+declare const b: BB
+>b : Symbol(b, Decl(deleteExpressionMustBeOptional.ts, 22, 13))
+>BB : Symbol(BB, Decl(deleteExpressionMustBeOptional.ts, 14, 1))
+
+delete f.a
+>f.a : Symbol(Foo.a, Decl(deleteExpressionMustBeOptional.ts, 0, 15))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>a : Symbol(Foo.a, Decl(deleteExpressionMustBeOptional.ts, 0, 15))
+
+delete f.b
+>f.b : Symbol(Foo.b, Decl(deleteExpressionMustBeOptional.ts, 1, 13))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>b : Symbol(Foo.b, Decl(deleteExpressionMustBeOptional.ts, 1, 13))
+
+delete f.c
+>f.c : Symbol(Foo.c, Decl(deleteExpressionMustBeOptional.ts, 2, 25))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>c : Symbol(Foo.c, Decl(deleteExpressionMustBeOptional.ts, 2, 25))
+
+delete f.d
+>f.d : Symbol(Foo.d, Decl(deleteExpressionMustBeOptional.ts, 3, 20))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>d : Symbol(Foo.d, Decl(deleteExpressionMustBeOptional.ts, 3, 20))
+
+delete f.e
+>f.e : Symbol(Foo.e, Decl(deleteExpressionMustBeOptional.ts, 4, 14))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>e : Symbol(Foo.e, Decl(deleteExpressionMustBeOptional.ts, 4, 14))
+
+delete f.f
+>f.f : Symbol(Foo.f, Decl(deleteExpressionMustBeOptional.ts, 5, 32))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>f : Symbol(Foo.f, Decl(deleteExpressionMustBeOptional.ts, 5, 32))
+
+delete f.g
+>f.g : Symbol(Foo.g, Decl(deleteExpressionMustBeOptional.ts, 6, 33))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>g : Symbol(Foo.g, Decl(deleteExpressionMustBeOptional.ts, 6, 33))
+
+delete f.h
+>f.h : Symbol(Foo.h, Decl(deleteExpressionMustBeOptional.ts, 7, 14))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>h : Symbol(Foo.h, Decl(deleteExpressionMustBeOptional.ts, 7, 14))
+
+delete f.i
+>f.i : Symbol(Foo.i, Decl(deleteExpressionMustBeOptional.ts, 8, 10))
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+>i : Symbol(Foo.i, Decl(deleteExpressionMustBeOptional.ts, 8, 10))
+
+delete f.j
+>f : Symbol(f, Decl(deleteExpressionMustBeOptional.ts, 20, 13))
+
+delete a.a
+>a : Symbol(a, Decl(deleteExpressionMustBeOptional.ts, 21, 13))
+
+delete a.b
+>a : Symbol(a, Decl(deleteExpressionMustBeOptional.ts, 21, 13))
+
+delete b.a
+>b : Symbol(b, Decl(deleteExpressionMustBeOptional.ts, 22, 13))
+
+delete b.b
+>b : Symbol(b, Decl(deleteExpressionMustBeOptional.ts, 22, 13))
+