Unhelpful error message when nested attributes are used with wrong repetition depth

[ellifteria]

When an incorrect repetition depth is used within a definition macro or an expression macro, Racket and DrRacket don't trace the error to the correct line.

In the following Rhombus code, x is used with the wrong repetition depth:

#lang rhombus/static/and_meta

def [[x, ...], ...] = [[1, 2], [3, 4]]

[x, ...]

And Racket throws an error that correctly traces the wrong repetition depth to the correct line:

example.rhm:5:1: x: used with wrong repetition depth
  in: x
  expected: 2
  actual: 1
  #(73 1)

However, if an incorrect repetition depth is used with a definition or expression macro (shown here as a definition macro but switching defn.macro to expr.macro gives the same error message), as in this code where a.var is used with the wrong depth:

#lang rhombus/static/and_meta

meta syntax_class SyntaxClass
| '$variable':
    field [var, ...] = [variable]

defn.macro 'random_macro [$(a :: SyntaxClass), ...]':
  def [[b, ...], ...] = [[a.var, ...]]
  '1'

The error message traces the wrong usage to a Racket file in the Rhombus source instead of the line in the macro where the wrong repetition depth is used:

Library/Racket/8.13/pkgs/rhombus-lib/rhombus/private/amalgam/pattern-variable.rkt:112:64: a: used with wrong repetition depth
  in: a.var
  expected: 2
  actual: 1

Ideally, the error message should trace the error back to line 8 in this file, instead of to a Racket file in the Rhombus source.

[usaoc]

This is a problem specifically with pattern variables, which handle repetitions in a unique way (related: #534). For example, the following program can reproduce the same unhelpful error message:

#lang rhombus

syntax_class SyntaxClass
| '$variable':
    field [var, ...] = [variable]

match '[a, b, c]'
| '[$(a :: SyntaxClass), ...]':
    [[a.var, ...]]

and the following program, too:

#lang rhombus

match '[a, b, c]'
| '[$(pattern a
      | '$variable':
          field [var, ...] = [variable]),
    ...]':
    [[a.var, ...]]

In fact, the source location points to the repetition handler in pattern variables.