Add lint long_variable_names

[JurrianFahner]

The lint is configurable by using max-variable-name-length.

Related #644 this PR only concerns the variable length

changelog: [long_variable_names]: enable variable length check in clippy

[rustbot]

r? @Jarcho

rustbot has assigned @Jarcho.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[JurrianFahner]

r? @llogiq thanks for your clippy workshop today! Looking forward for your feedback.

[JurrianFahner]

I doubt whether the default value is well chosen. 30 seems ok for most of the use cases. But for the clippy source it was needed to create some different configurations too.

[llogiq]

Yeah, so I'd like to make sure that we have some benefit if we actually have that lint warn. I figure we either make it a pedantic lint or we set a far higher default threshold. When in doubt, you can run lintcheck.

Otherwise this looks good to merge.

[llogiq]

Looks good to me. Can you squash your commits please?

[llogiq]

I will start the FCP for this lint later today.

[samueltardieu]

Thanks for incorporating the feedback. Here is another round of how to make things more efficient, with even simpler code.

[samueltardieu]

I'd prefer something like that, but it is mostly nitpicking:

Suggested change

	format!(
	"use of a long variable name, it is longer than the configured `max-variable-name-length` of {} characters",
	self.max_variable_name_length
	),
	None,
	format!("reduce the length of the long variable name with at least {length_diff} characters"),
	format!(
	"variable name is longer than the configured `max-variable-name-length` ({} characters)",
	self.max_variable_name_length
	),
	None,
	format!("rename the variable to not exceed the maximum length"),

[JurrianFahner]

I agree with the changes in line 65. However line 69 contains information that a developer can use to make decisions in what to do, for example to remove one word from the variable.

[Centri3]

Updated your description to prevent fully closing #644, which I assume is undesired 😅

[samueltardieu]

That's much improved, thanks!

Changes made

[JurrianFahner]

That's much improved, thanks!

You're welcome! Thanks for the quick feedback loop, so we were able to finish it fast. It was a nice learning experience on how to build a first lint.
I lost quite some time on building on windows, but when I switched to linux in WSL the iterations became more quick.