def message

bend-lint-rules@0.2.0.0 · language/decreasing_call.bend:204

import Base
import bend-lint-api@0.2.0.0/linter/lint.bend as Lint

204def message(verdict: Verdict, loop: String, source: String, args: List<&2, Lint.Node>) -> String:
205  match verdict:
206    case Fails{+at, param}:
207      loop
208        ++ " calls itself here, but argument "
209        ++ ordinal(at)
210        ++ " (`"
211        ++ Lint.Span.text(source, Lint.Node.span(List.get(&2, Lint.Node, args, at)))
212        ++ "`) is neither the parameter "
213        ++ param
214        ++ " unchanged nor a part of it that a match took apart, and the arguments before it are unchanged. Bend reads the arguments left to right, so it cannot prove the loop ends, and the check fails (\"a decreasing self-call\"). Put the parameter that shrinks first, pass the ones before it unchanged, and pass a part of it that a match took apart (`p` of `case 1n+p:`)."
215    case _:
216      loop
217        ++ " calls itself here with every argument unchanged, so the loop would never end, and the check fails (\"a decreasing self-call\"). Pass a part of the parameter that shrinks, one that a match took apart (`p` of `case 1n+p:`)."