Proc macros in LS

[mkaput]

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Steps

MVP

• [ ] scarb proc-macro-server
• [ ] Pre-MVP: Implement ProcMacroHost that will JUST declare attributes/macros without doing expansion proper.
• [ ] MVP: ProcMacroHost on LS side (note: forget diags, forget “demonization”, forget watching for Scarb.toml changes)

To triage and designate in separate tasks

• [ ] Caching
• [ ] Watch for Scarb.toml/Scarb.lock changes -- preferably just hook on output of New Project Model
• [ ] Demonization (watch for death of expander server or not answering on time, research this)
• [ ] Handle diagnostics (we don't know yet how this should work, research this)
• [ ] Watch for proc macro source code changes (is this feasible?)
• [ ] Triage/Research: status indicator or progress bar?
• [ ] Triage/Research: how to handle not yet built macros (i.e. who and how should call scarb build on macro package)