False positive on splice compile error

[edsrzf]

The code below produces the error:

compile error: splice can only be used in function parameters and data constructors, it has no effect here

(do (def (n) [(splice [])]) n)

(The original code was a let, which I reduced, and this is the expansion.)

I believe this is a false positive, since the splice form is in a data constructor. These variations of the code don't cause the error:

(def (n) [(splice [])]) n       # no do wrapper
(do (def n [(splice [])]) n)    # no destructuring 
(do (def (n) [1(splice [])]) n) # extra element before the splice

[sogaiu]

It looks like a false positive to me too.

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Minor note, I think it's a little more "janet-familiar" to express the original as:

(do (def [n] [(splice [])]) n)

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Possibly related:

• Disallow splice in semantically useless positions rather than silently ignoring. #1121
• Misbehavior of logical operators and/or with splice #1117

[bakpakin]

I see, looks like a bug due to a small optimization for defs, which in the case of an unpacking operation, never creates the literal in first place. E.g. (def [a b] [1 2]) is compiled in the same manner as (def a 1) (def b 2). I guess this doesn't work here due to the splice, so we would need to prevent this optimization.