fix(isolated-declarations): allow adding undefined to keyof parameter types (#27173)

A defaulted `keyof` parameter followed by a required parameter still reports TS9025, even though tsc 7 accepts it and emits `| undefined`. #27009 handled `readonly` but kept the other type operators on the error path.

The only other operators are `keyof` and `unique`. `keyof X` never includes `undefined`, and `unique symbol` can't appear in a parameter annotation, so every type operator can safely take `| undefined`.

When the rest of the type can't be resolved without a checker, like `(any | undefined) & keyof S`, this now adds a redundant `| undefined` where it used to preserve the annotation. The type is the same. It's the existing behavior for `any` unions, and tsc 7 isn't consistent there either: it widens `any | string` but not `any | keyof {}`.

## Example

```ts
export function keyOf(value: keyof Source = "value", required: string): void {}
```

Before:

```
x TS9025: Declaration emit for this parameter requires implicitly adding
| undefined to it's type. This is not supported with --isolatedDeclarations.
```

After:

```ts
export declare function keyOf(value: keyof Source | undefined, required: string): void;
```

The existing `default-parameter-type-kinds` and `function-parameters` snapshots lose five TS9025 diagnostics. The `keyof` declarations match tsc 7.0.2 output apart from parenthesization.

Follow-up to #27009 (#26944).

crates/oxc_isolated_declarations/src/function.rs

@@ -334,10 +334,8 @@ fn can_add_undefined(ts_type: &TSType<'_>) -> bool {
         | TSType::TSTupleType(_)
         | TSType::TSTypeLiteral(_)
         | TSType::TSTemplateLiteralType(_)
-        | TSType::TSThisType(_) => true,
-        TSType::TSTypeOperatorType(operator) => {
-            operator.operator == TSTypeOperatorOperator::Readonly
-        }
+        | TSType::TSThisType(_)
+        | TSType::TSTypeOperatorType(_) => true,
         TSType::TSParenthesizedType(parenthesized) => {
             can_add_undefined(&parenthesized.type_annotation)
         }

crates/oxc_isolated_declarations/tests/snapshots/default-parameter-type-kinds.snap

@@ -9,18 +9,18 @@ interface Source {
 	value: string;
 }
 export declare function mapped(value: { [K in keyof Source]: Source[K] }, required: string): void;
-export declare function keyOf(value: keyof Source, required: string): void;
+export declare function keyOf(value: keyof Source | undefined, required: string): void;
 export declare function readonlyTuple(value: readonly [string] | undefined, required: string): void;
 export declare function intersection(value: {
 	optional?: string;
 } & number[] | undefined, required: string): void;
-export declare function operatorIntersection(value: (keyof Source) & string, required: string): void;
-export declare function unknownOperatorIntersection(value: unknown & keyof Source, required: string): void;
+export declare function operatorIntersection(value: (keyof Source) & string | undefined, required: string): void;
+export declare function unknownOperatorIntersection(value: unknown & keyof Source | undefined, required: string): void;
 export declare function unresolvedIntersection<T>(value: T & string, required: string): void;
 export declare function allUnknownIntersection(value: unknown & unknown | undefined, required: string): void;
 export declare function unresolvedUndefinedUnionIntersection<T>(value: (T | undefined) & string, required: string): void;
-export declare function unknownUndefinedUnionOperatorIntersection(value: (unknown | undefined) & keyof Source, required: string): void;
-export declare function anyUndefinedUnionOperatorIntersection(value: (any | undefined) & keyof Source, required: string): void;
+export declare function unknownUndefinedUnionOperatorIntersection(value: (unknown | undefined) & keyof Source | undefined, required: string): void;
+export declare function anyUndefinedUnionOperatorIntersection(value: (any | undefined) & keyof Source | undefined, required: string): void;
 export declare function unresolvedNeverOperatorIntersection<T>(value: T & never & keyof Source, required: string): void;
 export declare function voidUnionUndefinedIntersection(value: (void | string) & undefined, required: string): void;
 export {};
@@ -37,42 +37,6 @@ export {};
  7 |   required: string,
    `----
 
-  x TS9025: Declaration emit for this parameter requires implicitly adding
-  | undefined to it's type. This is not supported with --isolatedDeclarations.
-    ,-[11:3]
- 10 | export function keyOf(
- 11 |   value: keyof Source = "value",
-    :   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- 12 |   required: string,
-    `----
-
-  x TS9025: Declaration emit for this parameter requires implicitly adding
-  | undefined to it's type. This is not supported with --isolatedDeclarations.
-    ,-[26:3]
- 25 | export function operatorIntersection(
- 26 |   value: (keyof Source) & string = "value",
-    :   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- 27 |   required: string,
-    `----
-
-  x TS9025: Declaration emit for this parameter requires implicitly adding
-  | undefined to it's type. This is not supported with --isolatedDeclarations.
-    ,-[31:3]
- 30 | export function unknownOperatorIntersection(
- 31 |   value: unknown & keyof Source = "value",
-    :   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- 32 |   required: string,
-    `----
-
-  x TS9025: Declaration emit for this parameter requires implicitly adding
-  | undefined to it's type. This is not supported with --isolatedDeclarations.
-    ,-[51:3]
- 50 | export function unknownUndefinedUnionOperatorIntersection(
- 51 |   value: (unknown | undefined) & keyof Source = "value",
-    :   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- 52 |   required: string,
-    `----
-
   x TS9025: Declaration emit for this parameter requires implicitly adding
   | undefined to it's type. This is not supported with --isolatedDeclarations.
     ,-[61:3]

crates/oxc_isolated_declarations/tests/snapshots/function-parameters.snap

@@ -22,7 +22,7 @@ export declare function withAnyUndefinedUnion(a: any | undefined, b: string): vo
 type Foo = {};
 export declare function withAnyTypeReferenceUnion(a: any | Foo, b: string): void;
 export declare function withAnyTypeReferenceUndefinedUnion(a: any | Foo | undefined, b: string): void;
-export declare function withAnyTypeOperatorUnion(a: any | keyof {}, b: string): void;
+export declare function withAnyTypeOperatorUnion(a: any | keyof {} | undefined, b: string): void;
 export declare function withAnyIntersectionTypeReferenceUnion(a: any | (Foo & {}), b: string): void;
 export declare function withUnknown(a: unknown | undefined, b: string): void;
 export declare function withUnknownUnion(a: unknown | string | undefined, b: string): void;
@@ -55,14 +55,5 @@ export {};
  27 |   return 2;
     `----
 
-  x TS9025: Declaration emit for this parameter requires implicitly adding
-  | undefined to it's type. This is not supported with --isolatedDeclarations.
-    ,-[38:42]
- 37 | export function withAnyTypeReferenceUndefinedUnion(a: any | Foo | undefined = {}, b: string): void { }
- 38 | export function withAnyTypeOperatorUnion(a: any | keyof {} = 1, b: string): void { }
-    :                                          ^^^^^^^^^^^^^^^^^^^^^
- 39 | export function withAnyIntersectionTypeReferenceUnion(a: any | (Foo & {}) = {}, b: string): void { }
-    `----
-
 
 ```