MiniWDL does not support map to struct coercion

[stxue1]

The unit test in the WDL spec attempts to implicitly coerce a map to a struct:

version 1.1

struct Words {
  Int a
  Int b
  Int c
}

workflow map_to_struct {
  String a = "beware"
  String b = "key"
  String c = "lookup"

  output {
    # What are the keys to this Struct?
    Words literal_syntax = Words {
      a: 10,
      b: 11,
      c: 12
    }

    # What are the keys to this Struct?
    Words map_coercion = {
      a: 10,
      b: 11,
      c: 12
    }
  }
}

MiniWDL currently cannot run this workflow:

2024-08-21 14:58:50.630 wdl.w:map_to_struct workflow start :: name: "map_to_struct", source: "unit_tests/map_to_struct.wdl", line: 9, column: 1, dir: "/home/heaucques/Documents/wdl-conformance-tests/20240821_145850_map_to_struct"
2024-08-21 14:58:50.632 wdl.w:map_to_struct miniwdl :: version: "v1.12.0", uname: "Linux pop-os 6.9.3-76060903-generic #202405300957~1721174657~22.04~abb7c06 SMP PREEMPT_DYNAMIC Wed J x86_64"
2024-08-21 14:58:50.654 wdl.w:map_to_struct workflow map_to_struct (unit_tests/map_to_struct.wdl Ln 9 Col 1) failed :: dir: "/home/heaucques/Documents/wdl-conformance-tests/20240821_145850_map_to_struct", error: "EvalError", message: "unusable runtime struct initializer, missing non-optional member(s) in struct Words: a b c", node: "output-map_coercion", pos: {"source": "/home/heaucques/Documents/wdl-conformance-tests/unit_tests/map_to_struct.wdl", "line": 23, "column": 26}
2024-08-21 14:58:50.655 wdl.w:map_to_struct aborting workflow
2024-08-21 14:58:50.655 miniwdl-run unusable runtime struct initializer, missing non-optional member(s) in struct Words: a b c :: error: "EvalError", node: "output-map_coercion", pos: {"source": "/home/heaucques/Documents/wdl-conformance-tests/unit_tests/map_to_struct.wdl", "line": 23, "column": 26}, dir: "/home/heaucques/Documents/wdl-conformance-tests/20240821_145850_map_to_struct"

When parsing the workflow with MiniWDL's internals, while it is able to parse, the struct keys are not properly propagated (I first encountered this here).

Post parse, literal_syntax is equal to {'a': 'Int', 'b': 'Int', 'c': 'Int'} and map_coercion is equal to {'a': 'Int', 'b': 'Int', 'c': 'Int'}, instead of the expected value.