Allow templates to be rendered without reply

[robinvdvleuten]

Something you'll need to render a template without a "reply" context. Like a notification email for example. This PR adds fastify.view() just for that.

[delvedor]

Awesome!
Can you also add a test to verify the output of fastify.view and update the documentation?

[robinvdvleuten]

@delvedor sure! Do you want all the same testcases as for reply.view or only one to confirm that it's working?

[delvedor]

Just one should be fine :)

[robinvdvleuten]

@delvedor so it turned out to be more difficult than initially thought. I made the renderer functions returning promises, so they can be used when calling in a non-response aware context (the functions had some send and header calls).

[mcollina]

CI is failing for Node 6.

I’m somewhat -1 on returning a promise in the renderer. The action was synchronous before and it become asynchronous now.

[robinvdvleuten]

@mcollina I brought back the original synchronous functionality (so no breaking changes 💪). The new fastify.render method is still using promises though, is that still a concern?

[mcollina]

There is no reason to have fastify.render return a promise as it's not an asynchronous operation.

[robinvdvleuten]

@mcollina but what about the _readCallback then?

[mcollina]

You are right. I would go for a callback if there is one, or a Promise if there is none.

[robinvdvleuten]

@mcollina I've updated the PR accordingly 👍