# Assertions about names an operator chooses, so a module states WHAT is
# forbidden and not how to phrase the refusal.
{ lib }:
let
  # One shape for both guards. Reports EVERY offender, not the first: fixing
  # one per rebuild is the slowest possible way to learn a rule.
  #
  # Offenders come after their label rather than before it, so one name and
  # five read the same — no English verb agrees with both.
  guard =
    {
      option,
      names,
      forbidden,
      hit,
      problem,
      forbiddenLabel,
      why,
    }:
    let
      offenders = lib.filter (n: lib.any (f: hit f n) forbidden) names;
      quote = xs: lib.concatMapStringsSep ", " (x: "'${x}'") xs;
    in
    {
      assertion = offenders == [ ];
      message = ''
        ${option} ${problem}: ${quote offenders}
        ${forbiddenLabel}: ${quote forbidden}

        ${why}
      '';
    };
in
{
  # No name may BE one of `reserved`.
  mustNotEqual =
    {
      option,
      names,
      reserved,
      why,
    }:
    guard {
      inherit option names why;
      forbidden = reserved;
      hit = f: n: f == n;
      problem = "has reserved name(s)";
      forbiddenLabel = "Reserved";
    };

  # No name may CONTAIN one of `fragments`.
  mustNotContain =
    {
      option,
      names,
      fragments,
      why,
    }:
    guard {
      inherit option names why;
      forbidden = fragments;
      hit = lib.hasInfix;
      problem = "has name(s) containing a reserved word";
      forbiddenLabel = "Forbidden as substrings";
    };
}