Can't define function over std.Vector(StructType) without building the type first

[jrfondren]

In this code:

local std = require "std"

struct S {
  k: int
}

std.Vector(S) -- compile fails without this line

terra main()
  var a = [std.Vector(S)].salloc():init()
  a:insert().k = 1
  a:insert().k = 2
  a:insert().k = 3
  for i = 0ULL, a:size() do
    std.printf("x[%llu].k: %d\n", i, a(i).k)
  end
  std.printf("#%llu\n", f(a))
end

terra f(v: &std.Vector(S)): uint64
  return v:size()
end

main()

Without the commented line, compilation fails:

/terra/src/terralib.lua:1105: attempting to use type S before it is defined.

stack traceback:
        [C]: in function 'error'
        /terra/src/terralib.lua:381: in function 'erroratlocation'
        /terra/src/terralib.lua:1524: in function 'getvalue'
        /terra/src/terralib.lua:1373: in function 'getentries'
        /terra/src/terralib.lua:1563: in function 'getvalue'
        /terra/src/terralib.lua:1373: in function 'getlayout'
        /terra/src/terralib.lua:1642: in function 'userfn'
        [string "/std.t"]:119: Errors reported during finalizing type
        /terra/src/terralib.lua:2986: in function 'docheck'
        /terra/src/terralib.lua:3120: in function 'checkexp'
        ...
        [string "/std.t"]:110: in function 'fn'
        /terra/src/terralib.lua:1250: in function 'Vector'
        t5.t:20: in function 'userfn'
        t5.t:20: Errors reported during evaluating Lua code from Terra
terra f(v: &std.Vector(S)): uint64
           ^
        /terra/src/terralib.lua:1843: in function 'evalluaexpression'
        /terra/src/terralib.lua:1850: in function 'evaltype'
        /terra/src/terralib.lua:1870: in function 'evaluateparameterlist'
        /terra/src/terralib.lua:1068: in function 'evalformalparameters'
        /terra/src/terralib.lua:1143: in function 'defineobjects'
        t5.t:3: in main chunk

[elliottslaughter]

I agree that it doesn't seem like this ought to fail. The struct S is clearly defined, and if you go take a look at the std.t source you'll see the Vector type is too.

Unfortunately I don't have time to dig in further right now, but it probably has something to do with Terra's ordering of compilation. If you want to help out, I'd trace through the compiler to see what difference that line makes; presumably there is some path (e.g., completing a type T when used as &T) that's missing that ought to be there.