Indentation inference for defmacros

[vemv]

(IDK if this had been talked about before)

Given an arbitrary macro that lacks :style/indent metadata, e.g. (defmacro fact [& forms], I'd find it most practical that CIDER inferred a sensible indent value for it.

A sensible rule of thumb is:

indent = <number of macro args before &>

For instance, [a b & c] has two arguments before &, so the inferred indent should be 2.

There occasionally exist macros without &, e.g.:

(defmacro foo [opts body]

For those, we can devise a similar rule of thumb:

indent = <number of macro args before an argument named body>

(or forms, tail, similar words)

So that foo would have an indent of 1.

I understand that this is not quite 'pure' in approach. But my experience over the years is that very few people, even among CIDER users, will remember to add the metadata manually.

Ultimately, users can of course always add metadata, which would override any inference.

WDYT?

Cheers - V

[vemv]

Another rule of thumb, is that if something is called approximately defrecord, then format it like defrecord. Same for defprotocol, etc.

(For these ones, it's safer to do this only if the custom macro's arglists are equal or a subset to those of their clojure.core counterpart)

[bbatsov]

Yeah, that'd be fine. That's similar to how SLIME used to work out indentation when it wasn't specified - by relying on the the names of some params (I think body and forms). In general I'm all for adding some sensible inference to simplify the lives of users.

[bbatsov]

You can check this out for some inspiration https://github.com/slime/slime/blob/master/contrib/slime-cl-indent.el