add support for empty nd-array syntax

[simeonschaub]

What's still missing here is the correct compat check, since this is
only supported in Julia 1.8. I wasn't sure how to check for this in
check_ncat_compat.

[c42f]

Awesome, this is the first PR to this repo!

For now, this will need the tests like [;;] ==> (ncat 2) added in test/parser.jl (actually this should be (ncat-2) because the 2 is stored in the flags, not as a child node in the tree. Search for similar tests to figure out where best to add them.

For interactively developing the parser and tests, I'd suggest using the itest_parse function which will check several things and do some pretty printing:

julia> include("test/test_utils.jl")
julia> itest_parse(JuliaSyntax.parse_atom, "[;;]")

# Code:
[;;]

# Green tree:
     1:4      │[error]                   ✘
     1:4      │  [ncat]
     1:1      │    [                        "["
     2:2      │    ;                        ";"
     3:3      │    ;                        ";"
     4:4      │    ]                        "]"
Error: unexpected closing token:
[;;]
Error: multidimensional array syntax not supported in Julia version 1.6 < 1.7:
[;;]

# SyntaxNode:
(error (ncat-2))

# Julia Expr:
:($(Expr(:error, :([;;]))))

# AST dump
Expr
  head: Symbol error
  args: Array{Any}((1,))
    1: Expr
      head: Symbol ncat
      args: Array{Any}((1,))
        1: Int64 2

# flisp Julia Expr:
:($(Expr(:error, "unexpected \";\"")))

Also, optional... but perhaps consider moving this logic to the top of parse_array, because that's the function which handles the rest of ncat syntax? On second though, I don't know if this is useful. Either way is fine and what you have is more direct.

I wasn't sure how to check for this in check_ncat_compat.

This should already work as-is, because you emit K"ncat" and check_ncat_compat just checks for that.

[c42f]

This should already work as-is, because you emit K"ncat" and check_ncat_compat just checks for that.

Oh, I see the problem... it's not the same version check as other ncat stuff which is in 1.7.

We could consider adding the version check immediately where you detect the K";"? The only issue with that is it will cause two related and somewhat redundant errors on Julia <= 1.6, one for ncat syntax and one for this particular empty array syntax. But perhaps we can live with that.

[simeonschaub]

We could consider adding the version check immediately where you detect the K";"? The only issue with that is it will cause two related and somewhat redundant errors on Julia <= 1.6, one for ncat syntax and one for this particular empty array syntax. But perhaps we can live with that.

Ok, I can do that. My initial thought was that we could maybe also just check if the ncat expression is otherwise empty in check_ncat_compat, but I wasn't sure how to do that.

[c42f]

just check if the ncat expression is otherwise empty in check_ncat_compat, but I wasn't sure how to do that

We'd have to add more sophisticated ways of looking back on the output to make that easy. That's possible, but I do like to avoid it because I think it leads to confusing code. I'd even like to remove peek_behind() completely but I'm not sure it's possible...

[c42f]

I'll fix these separately to keep them in sync with the actual tests (yeah, I need to improve the tooling so we don't need to repeat ourselves 😅 )

[simeonschaub]

Oops! Yeah, I think I was just thinking of the s-expression syntax instead of JuliaSyntax' one.

[c42f]

This looks excellent, thanks :-D