[Bug] TypeScript string autocomplete works in VS Code but not Monaco

Reproducible in vscode.dev or in VS Code Desktop?

• Not reproducible in vscode.dev or VS Code Desktop

Reproducible in the monaco editor playground?

• Not reproducible in the monaco editor playground

Monaco Editor Playground Link

Try typing document.addEventListener(" in both VS Code and the Monaco playground, with either JavaScript or TypeScript. In VS Code autocomplete shows a list of allowed event names. In Monaco there is no such suggestion.

This occurs in general with any string parameters - for example if a TypeScript function parameter type is "MyString1" | "MyString2", VS Code will autocomplete suggest those strings, but Monaco does not suggest anything.

Monaco Playground link demonstrating the problem

Monaco Editor Playground Code

// Most minimal repro:
type AllowedStrings = "MyString1" | "MyString2";
function test2(str : AllowedStrings) {}

// Then try typing: test2("

Reproduction Steps

With the most minimal repro code snippet shown previously, try typing:

test2("

Actual (Problematic) Behavior

In Monaco, no autocomplete is shown for the string parameter.

Expected Behavior

In VS Code, autocomplete is shown for the string parameter, suggesting the allowed strings "MyString1" and "MyString2". This is what Monaco should do as well.

Additional Context

Monaco is able to use the type information to correctly validate parameters - for example test2("MyString1") is allowed, and test2("invalid") is correctly marked as an error. So it seems the type information is there and working, it's just not being provided to autocomplete.

This issue makes it significantly harder to write common calls like addEventListener in Monaco outside of VS Code: autocompleting the allowed strings is very useful, and avoids the need for trial-and-error to get the right string.

Start with the linked Monaco Playground reproduction and the minimal TypeScript union-string example, then trace how Monaco handles autocomplete for string parameters compared with VS Code. The work is done when typing test2(" and document.addEventListener(" produces the allowed string suggestions without breaking existing validation.