e8f93447

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Self-weed: report unused configured roots, root-instances and root-modules

Weeder now reports configuration entries that no longer match anything,
treating stale roots as weeds in their own right (issue #154):

  * a `roots` pattern that matches no declaration,
  * a `root-instances` entry that matches no instance, and
  * a `root-modules` pattern that matches no module.

These print alongside the regular weeds and contribute to the
weeds-found exit code.

Only entries the user explicitly configured are reported -- defaults
(`Main.main`, `^Paths_.*`, `IsString`/`IsList`) are left alone, since
flagging a default the user never wrote is not actionable. Provenance is
tracked by a `Configured` wrapper on the three root fields, set from
whether the TOML field was present.

A `roots` pattern counts as matching if it names any declaration defined
in the analysed modules (`localDeclarations`), not merely an outputable
one, so a root naming a real type or constructor is not flagged just
because `unused-types` is disabled; a root matching only an external
symbol still is. When `type-class-roots` is set, `root-instances` is
ignored entirely and so is never reported.

To name the offending entry, compiled patterns carry their source string
(`CompiledRegex`), and reachability and dead-root detection share a
single `matchesInstancePattern` predicate.

Adds SelfWeeding and DefaultsNotReported integration tests; no existing
golden output changes.

Timeline