buildValidationFailureMessage function

String buildValidationFailureMessage(Result result, { int maxValueLength = 120, int maxErrorsToList = 20, })

Build a standardized, human friendly message for a failed Result.

Format (subject to small evolutionary changes, kept backwards friendly):

Validation failed (errors:

1. <expectation.description> code=<code> {data=
2. ... ... (remaining

This provides:

• Count of errors (quick scanning / logging)
• Value type & representative sample (actionable debugging)
• Each expectation's description (already path-aware) plus code & optional data
• Compact truncation safeguards for very large values

Implementation

String buildValidationFailureMessage(
  Result result, {
  int maxValueLength = 120,
  int maxErrorsToList = 20,
}) {
  assert(!result.isValid, 'Only call buildValidationFailureMessage on invalid results');

  final value = result.value;
  var valueRepr = _safeValueString(value);
  if (valueRepr.length > maxValueLength) {
    valueRepr = '${valueRepr.substring(0, maxValueLength)}…';
  }

  final buffer = StringBuffer();
  buffer.write('Validation failed (errors: ${result.expectationCount})');
  buffer.write(' for value (${value.runtimeType}): ');
  buffer.writeln(valueRepr);

  final toShow = result.expectations.take(maxErrorsToList).toList(growable: false);

  for (var i = 0; i < toShow.length; i++) {
    final e = toShow[i];
    buffer.write('  ${i + 1}) ');
    buffer.write(e.description);

    if (e.code != null) buffer.write(' [code=${e.code}]');
    if (e.data != null && e.data!.isNotEmpty) buffer.write(' {data=${e.data}}');
    buffer.writeln();
  }

  final remaining = result.expectationCount - toShow.length;
  if (remaining > 0) {
    buffer.writeln('  … ($remaining more not shown)');
  }

  return buffer.toString().trimRight();
}