TypeScript 3.6 Incremental and Build API Support

Feature request

TS 3.6 officially supports Incremental and Build (aka Project References) APIs: https://devblogs.microsoft.com/typescript/announcing-typescript-3-6/#apis-to-support-build-and-incremental

Is your feature request related to a problem? Please describe.

Support following syntax in tsconfig.json:

{
    "compilerOptions": {
        // The usual
        rootDir: './src',
        paths": {
            "my-core-lib": ["../core"]
        }
    },
    "references": [
        {"path": "../core"}
    ]
}

By design the composite project that resides in ../core directory will be built before project in cwd.

Using the above setup user can refer to my-core-lib by name (instead of relative paths) from main Next.js project.

Describe the solution you’d like

1. Ideally, since Next.js now offers first-class support of TS, it can use TSC instead of Babel, but as I see, it can have performance problems as well as backward compatibility issues. And obviously it will require effort.
2. Alternatively, as a limited support MVP, we can use new TS APIs to build references only (and watch them too), not the main Next.js project, which still will be built using Bebel. This implies that my-core-lib is somehow linked to Next.js project’s node_modules (via Lerna or Yarn Workspaces).
3. Worst case scenario is to run tsc --build --watch and next in parallel, but this will build Next.js project twice and cause other nasty race conditions like failed Next.js build at first when referenced lib is being built (possible solution: tsc --build && (tsc --build --watch & next)). This also needs links in node_modules.

Describe alternatives you’ve considered

No clear alternatives since TS Babel preset just removes types and does not do any actual compilation. I only see several workarounds how we can tell Babel to compile things outside of the main project, this config may be auto-generated based on references.

There’s an issue https://github.com/Microsoft/TypeScript-Babel-Starter/issues/35.

Additional context

None.

[jeremy-coleman]

im fairly certain they dont intend to properly support typescript. your 2 best options are to:

1. precompile, for example, src transpile to-> app -> ‘(cli) next app’
2. move your ts files to a workspace package and import the transpiled stuff as single components into pages (so your next project is mostly empty). - this is best imo, but can cause links to become unclickable in your terminal, which is a terrible dev experience

[balazsorban44]

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