merge def var meta-data from the expression and the var-name

[retrogradeorbit]

Please answer the following questions and leave the below in as part of your PR.

• I have read the developer documentation.

• This PR corresponds to an issue with a clear problem statement.

• This PR contains a test to prevent against future regressions

Fixes issue #801

[borkdude]

This is still not the proper solution for defs that are defined by macros. Compare this in Clojure and bb:

(defmacro foodef [sym & body]
  `(do (def ~sym ~@body)))

(foodef x 1)

(prn (meta #'x))

To properly test this, I think it would be good to include the macro examples.

[borkdude]

Completed the PR here:

2b8751f

Couldn't hurt to receive a post-hoc review.

[retrogradeorbit]

what does the with-top-level-loc do? can you debrief me on that?

[retrogradeorbit]

Compare this in Clojure and bb

I see. missing again...

*top-level-location* is storing the extra metadata of the... outermost level of the macro?

What is top-level?

[borkdude]

@retrogradeorbit Yes! What SCI does now is that it remembers the top level location of a form that is analyzed. Also, when expanding a macro, the expanded form gets the locations of the unexpanded forms. These two combined:

(defmacro foodef [x v] `(def ~x ~ v))

(foodef x 1) ;; expression with metadata line 3
;;=> '(def x 1) ;; metadata is merged, so line 3 is preserved 

This above is the case you covered.
But when doing something like this:

(defmacro foodef [x v] `[(def ~x ~ v)])

e.g. wrap the expansion in a vector, the def form won't have any metadata, so we remember the top level metadata of the vector and use that in def.

For top-level do expressions, clojure has special semantics, so we do a similar thing there: we remember the top level location of the do expression while analyzing every do child.

[borkdude]

Another (maybe better) example is this one:

(defmacro foodef [sym & body]
  `(when (odd? 1)
     (def ~sym ~@body)))

(foodef x 1)

The def expression in the macro has no metadata (after expansion), so we piggyback on the metadata the top level expression.

[retrogradeorbit]

Great information. Thankyou!