Expand macros in window frames

[dannote]

Allow :frame to expand macros before validating that the result is a fragment.

Today this works:

windows: [
  recent: [
    order_by: result.date,
    frame: fragment(
      "RANGE BETWEEN INTERVAL 10 DAYS PRECEDING AND INTERVAL 10 DAYS FOLLOWING EXCLUDE CURRENT ROW"
    )
  ]
]

but an equivalent helper is rejected before expansion:

defmacro range_between(start_boundary, end_boundary, opts \\ []) do
  exclude = Keyword.get(opts, :exclude, :no_others)

  quote do
    fragment(
      unquote("RANGE BETWEEN #{start_boundary} AND #{end_boundary} EXCLUDE #{exclude}")
    )
  end
end

windows: [
  recent: [
    order_by: result.date,
    frame:
      range_between(
        "INTERVAL 10 DAYS PRECEDING",
        "INTERVAL 10 DAYS FOLLOWING",
        exclude: "CURRENT ROW"
      )
  ]
]

I ran into this while working on QuackDB, a new DuckDB adapter for Elixir. DuckDB supports richer frame clauses such as ROWS, RANGE, GROUPS, and EXCLUDE, and QuackDB could expose reusable helpers for those clauses instead of requiring users to write frame fragments inline.

The validation stays the same: after expansion, the frame still has to be a fragment. Non-fragment expansions continue to raise the existing error.

[josevalim]

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