using projectService.setHostConfiguration in a plugin is invalid

[mlgq]

🔎 Search Terms

enable plugin
setHostConfiguration

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about typescript plugin

export = function init(modules: { typescript: typeof TS }) {
    return {
        create(info: TS.server.PluginCreateInfo) {
            // @ts-expect-error: access private property
            if (!info.project.projectService.hostConfiguration.extraFileExtensions.some(o => o.extension === ".ext")) {
                info.project.projectService.setHostConfiguration({
                    extraFileExtensions: [
                        {
                            extension: ".ext",
                            isMixedContent: false,
                            scriptKind: modules.typescript.ScriptKind.Deferred
                        }
                    ]
                })
            }
            return info.languageService
        }
    }
}

🙁 Actual behavior

The language service should add files with the ext extension to the project

🙂 Expected behavior

The file with the ext extension was not added to the project