Enable used_underscore_binding clippy lint

[findepi]

_var is a convention to indicate unused variables or unused struct members.
As such, these members should indeed not be used.

used_underscore_binding clippy lint seems to be enforcing that. let's enable it in the workspace

datafusion/Cargo.toml

Line 185 in 7fde24a

[workspace.lints.clippy]

[ding-young]

take

[ding-young]

Hi, @findepi
I've set used_underscore_binding=deny and renamed each _var that was actually used or passed down as fn arg to var. However, this gives another clippy warning only_used_in_recursion in following code.

datafusion/datafusion/optimizer/src/push_down_limit.rs

Lines 51 to 55 in c176533

	fn rewrite(
	&self,
	plan: LogicalPlan,
	_config: &dyn OptimizerConfig,
	) -> Result<Transformed<LogicalPlan>> {

There are few cases like above where replacing _config with config gives only_used_in_recursion warning, which says I should go back and prefix it with an underscore: _config. I can simply put #[allow(clippy::used_underscore_binding)] on these cases, but suppressing the lint doesn't feel like a clean solution.

Do you have any suggestions about this issue? Thank you :)

[findepi]

We could move logic of PushDownLimit::rewrite to make it inherent method (impl PushDownLimit block).
This way we could recurse without threading useless config parameter. It would be slightly better in a sense that it would indeed use less stack space to recurse.
Or we can simply suppress one of the conflicting lints:

#[allow(clippy::used_underscore_binding)] // for recursive call only
self.rewrite(new_filter, _config)

[Ramjee194]

can you assign this issue #14649

[ding-young]

Hi @Ramjee194, I assigned myself with writing "take" (you can also do this for other issues, too!) and already working on this issue. :)