Custom directives for NextJs 13

[CarlOlson]

NextJs 13 introduces a new app directory for utilizing server components. Client components imported by a server component must have a "use client"; directive similar to strict mode. Using raw doesn't work because the directive must be above all code/imports.

Here are some ideas I thought of:

// 1. With a directive at the top of file
"use client"

// 2. At anywhere in the top level with a compiler directive
@@directive("use client")

// 3. Change %%raw to put code (or just directives) above imports
%%raw(`"use client";`)

And since so many files will have the same name, #4874 would also help with a big pain point of using NextJs w/ ReScript.

[sairion]

@mununki I'd like to know if it this can be achievable via ppx kind of userland apporoach

[mununki]

@mununki I'd like to know if it this can be achievable via ppx kind of userland apporoach

Don' think it is achievable without compiler js emitter change.
See #5998

[cristianoc]

In upcoming 10.1.3.