[brenelz]

A TypeScript entry written as the README shows (import main from "./app.rx"; app.mount(main(app))) fails rx-tsc --noEmit with TS1192: Module './app.rx' has no default export. Separately, with "include": ["src"] and a .d.rx in src/, rx-tsc crashes with languageId not found for …/users.d.rx and then Error: !!sourceScript from Volar's proxyCreateProgram.

Root cause

The TSX projection (spec/13 TY-1c) emits the default component as export function App(props: any) plus export const __view, and nothing as a default export. At run time the compiled entry's default export is main(__rt) (spec/11 CP-4a), so TypeScript sees no default where JavaScript gets one. For the crash: .rx is a program extension, so include globs also match .d.rx. The language plugin returned no language id for those files, and Volar's tsc asserts that every program file has a source script.

What changed

• The prelude gains export type Main = (app: object) => () => View;, a function of either build's createApp app that gives the view app.mount (or the server's app.stream) takes. A module with export default component now ends its projection with declare const __main: __.Main; export default __main;. The line is appended after the existing output, so the component's own mappings are unchanged. The type is in the prelude rather than taken from @reactivescript/runtime, because the prelude must resolve without the runtime installed (ref's type runner has no copy), and createApp's declared return type does not list the __rt helpers anyway.
• The crate (compiler/src/project.rs, prelude.ts) and ref (ref/types/project.ts) make the same change, since crate.ts --project compares them text for text.
• The language plugin gives .d.rx its own language id and an empty TypeScript module (export {}), so a .d.rx that include picks up no longer stops the program.
• compiler/src/prelude.ts line 12 still had the \`` escapes copied from ref's template literal, so crate.ts --projectfailed onmainwithFAIL prelude`. The fix changes only a comment.

Verification

• cargo test --release in compiler/: a new test checks that an entry's projection has exactly one default export, that App keeps its mapping, and that a dependency without a default component gets no default export.
• node test/tsc.js in tooling/rx-language-server/ (now also needs npm run build in runtime/). New checks:
  • the README's src/main.js snippet, read from README.md, type-checks against the built runtime's types;
  • app.stream(main(app), sink) type-checks with the server build;
  • app.mount(main), with main uncalled, fails with TS2345;
  • a .d.rx and the JS module it declares pass with "include": ["."].
• npm test in tooling/rx-language-server/: 16/16 and 8/8.
• In ref/:
  • npm run crate: 364/364.
  • npm run crate -- --project: 209/209, with 12,421 mappings holding.
  • npm run types and RX_CRATE=1 npm run types: 176 pass each.
  • npm test: no failures.
• A copy of a Vite template using 0.3.1, with its @ts-expect-error lines and its "exclude": ["src/**/*.d.rx"] removed, passes rx-tsc --noEmit with this branch. It crashes with the published 0.3.1.

Left open

• The default export is emitted wherever a default component exists, dependencies included, because the editor analyzes every file as its own entry. This is safe while the checker refuses default imports between .rx files (NOT_EXPORTED, MO-6), but MO-1c says a dependency may have a default component. If that import is ever allowed, the importer's projection should name the component (import { Badge as Tag }).
• A compiled entry exports only default, yet the projection still exports export component Foo and other named exports, so JavaScript can import names that do not exist at run time.
• An entry with no default component still compiles to a main default, but its projection has none.
• Main takes any object; a narrower type needs an app type exported from the runtime.
• The new default export line has no mapping onto the .rx, so go-to-definition on the imported main lands nowhere.
• A .d.rx's own types are not checked; projecting it through the crate's declaration_file would check them, but with no mappings back.

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