What is the future of JSI?

[vmoroz]

It is so surprising to see the new hermes.h file added to the jsi folder.
For a long time there was an impression that JSI is supposed to be a cross JS-engine API, but now it has the hermes.h file.
Moreover we now have two hermes.h files and we must pray to the compiler gods which one they choose.

So, am I correct to assume that:

• JSI is no longer is seen as a cross JS-engine API.
• RN is going to support only Hermes.

[tmikov]

Absolutely not correct. If anything, this improves JSI's cross-engine support, because each engine can freely add engine-specific extensions declared as interfaces. We are jumping through a lot of hoops precisely in order to keep JSI engine-neutral.

The jsi directory contains declarations of interfaces with their UUIDs. The Hermes-specific ones are simply in a file called jsi/hermes.h. We could have just put them in jsi.h, but this felt cleaner. This enables developers to query for these interfaces at runtime without creating an explicit Hermes dependency. If other engines have engine specific interfaces, we will happily add those too.

You are correct that the naming of the file is confusing. I hadn't noticed that. However it should never be included just as <hermes.h> - it should always be <jsi/hermes.h>, so there shouldn't be a problem. In any case, we will try to fix it.

I am not aware of any plans to make RN coupled to Hermes. I am pretty sure they would view that as a bug.

[tmikov]

We will probably rename it to hermes-interfaces.h

[vmoroz]

Awesome! Thank you, @tmikov , for the clarifications!
May I propose to establish some engine-specific naming conventions like jsi-hermes.h, jsi-jsc.h, etc.?