Allow `satisfies` in string enum member initializers

🔍 Search Terms

satisfies, enum

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

I suggest that TypeScript should allow this:

enum Foo {
  Foo = "Foo" satisfies "Foo"
}

Currently this is treated as a computed enum member and requires number type, despite nothing being actually computed here.

📃 Motivating Example

With isolatedModules/isolatedDeclarations enabled references in enum members are restricted. For example, this does not compile with isolatedDeclarations:

const FOO = "Foo"

enum Foo { Foo = FOO }
// Error: Enum member initializers must be computable without references to external symbols with --isolatedDeclarations.

satisfies here will ensure that Foo is properly typed while not referring to external symbols:

const FOO = "Foo"

enum Foo { Foo = "Foo" satisfies typeof FOO }

💻 Use Cases

See motivating example above.

Start by reproducing the string enum examples with and without satisfies, including the isolatedDeclarations case described in the issue. Trace how enum member initializers are classified and tested, then verify that accepted string initializers preserve the intended type restrictions without changing emitted JavaScript.