Unused lint does not rewrite suppressed warnings #24055
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Partially duplicates reporter logic; reporter could auto-apply actions, maybe keying off diagnostic ID.
Instead of testing whether to emit actions by probing suppressions, just let the reporter apply LintWarning actions when the warning is actually reported.
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Fixes #24009
Why was the ticket worth tackling?
Lints are inherently imprecise (the "unused" lint, in particular, runs after typer and merely infers usages), so that it is necessary to provide mechanisms to "suppress" them, namely
-Wconfand@nowarn. Even if a lint warning is correct, it may not be helpful. For example, the user may want to retain certain unused imports so that they are always available (Decorators) and so that the file "header" isn't subject to repeated edits or reformatting. (See-Yimports.)But it's also important to address warnings, so that
-rewritemight be enabled "by default" and not only for one-off migrations for which manual edits are expected.Therefore it should be possible to selectively apply rewrites proposed by linters.
Otherwise, linting and rewriting are much less useful.
How I fixed it
It is natural not to rewrite lints that are suppressed. Only "unused imports" emits "code actions" under
-rewrite, so the lint was improved to avoid adding actions ifctx.run.suppressions(for@nowarn) or-Wconfsay that the warning won't be reported. That mechanism is imprecise, so this filter is moved directly to the reporter (when it reports), which applies actions forLintWarningonly.CheckUnusedis tweaked to emit onlyLintWarning, with the additional tweak that anorigincan be a distinguished value to meanNoOrigin. (The origin is just a string, alas, subject to an arbitrary regex pattern match.) It is also tweaked to always calculate the code action. As suggested by a previous reviewer (@tgodzik I presume), this makes the action available to tooling. (The imports rewrite was conceived as a quick internal tool and not as a general code formatter. Used interactively, that may be more convenient, but I haven't tried it.)Why is this PR worth reviewing?
Certain components emit rewrites directly; for example, the parser might test certain conditions (such as migration), warn about deprecated syntax, and then add a rewrite to contemporary syntax. This PR offers a path toward a more general mechanism: emit a diagnostic with an associated action, and let the user control whether to see the diagnostic and therefore whether to apply the action under
-rewrite.This PR turns out to be more complex in UX than in code.
What's the worse that could happen?
The import action code in
CheckUnusedis no longer gated by-rewrite, which may be acceptable.