proposal: `no_wildcard_variable_uses`

[pq]

<no_wildcard_variable_uses>

Description

Do not use wildcard parameters or variables.

Details

There's a proposal to change the language so that (at least) parameters and local variables named _ (e.g., wildcards) become non-binding. When that happens, existing code that uses wildcard parameters or variables will break.

Enabling this lint now will make it less breaking to make _ non-binding in a future Dart release.

Kind

Error

Bad Examples

var _ = 1;
print(_); // LINT

void f(int __) {
  print(__); // LINT multiple underscores too
}

Good Examples

for (var _ in [1, 2, 3]) count++;

try {
  ...
} catch (_) {
  ...
}

var [a, _, b, _] = [1, 2, 3, 4];

Discussion

#51221

cc @dart-lang/language-team

Discussion checklist

• List any existing rules this proposal modifies, complements, overlaps or conflicts with.
• List any relevant issues (reported here, the SDK Tracker, or elsewhere).
• If there's any prior art (e.g., in other linters), please add references here.
• If this proposal corresponds to Effective Dart or Flutter Style Guide advice, please call it out. (If there isn't any corresponding advice, should there be?)
• If this proposal is motivated by real-world examples, please provide as many details as you can. Demonstrating potential impact is especially valuable.

[munificent]

I know I suggested this name, but now that I think about it, it would probably be better for the name to emphasize that it's using a variable whose name is a wildcard that's the issue, not declaring one. Maybe "do_not_use_wildcard"?

[pq]

Ah, right. It's a good point. I updated to no_wildcard_variable_uses (since we have more no_s than do_not_s) but do_not_use_wildcard_variables would be fine too.

Open to other ideas too!

/cc @bwilkerson

[pq]

Given the support in #51221, I'm going to transition this to accepted and offer a simple implementation. (We don't have to land that obviously.)