AST of short form functions

[c42f]

A pain point when writing macros is detecting all the types of things which might be lowered to functions and correctly extracting the formal arguments. This is due to

1. Existence of both short form and long form function definitions
2. The argument lists of anonymous functions being parsed into varying inconsistent Expr forms

JuliaSyntax already deals with part (2) of this.

I wonder if we should also deal with part (1) by emitting a clearer AST.

Currently we have

julia> parsestmt(SyntaxNode, "f()::T = 1")
line:col│ tree                                   │ file_name
   1:1  │[=]
   1:1  │  [::-i]
   1:1  │    [call]
   1:1  │      f
   1:6  │    T
   1:10 │  1

But it would be easy to change this into

julia> parsestmt(SyntaxNode, "f() = 1")
line:col│ tree                                   │ file_name
   1:1  │[function-=]
   1:1  │  [call]
   1:1  │    f
   1:7  │  1

And to have a syntax flag "=" set on the function node to indicate it was short-form syntax.

[c42f]

Well this was easy and I nerd sniped myself. so I just went and implemented it.

@JeffBezanson thoughts? Could be nice if macro authors didn't have to simulate this bit of lowering. It does depart from the surface syntax a little by adding semantics during parsing. That's always a hard call but I feel like the AST might be an improvement in this case.

[c42f]

Managed to chat to Jeff about this and he seems good with it. So I think we go for it :)