We should extend `--explain` to include config options

[xFrednet]

Clippy has an --explain command to display the lint documentation in the console. Ideally, we'd like to expand the command to include the configurations, which effect the lint emission. This is already done for Clippy's lint list.

Here is an example for such a lint: borrow_as_ptr

This implementation could take inspiration from how we collect the metadata for our lint list:

rust-clippy/clippy_lints/src/utils/internal_lints/metadata_collector.rs

Line 162 in 3cf2c17

fn get_lint_configs(&self, lint_name: &str) -> Option<String> {

CC: #9880

[blyxyas]

This would require moving metadata_collector.rs out of internal_lints and removing this #[cfg] feature check.

Btw, why does this feature (internal) exists? rustup downloads compiled artifacts, so unused code gets removed AFAIK.

If the feature exists because of compile-times, maybe we should remove it as between times from cargo build --features internal to cargo build there's only a 1.4% difference (in my machine). I think that's negligible.

[xFrednet]

It would be good if we could find a way, to connect the data without enabling all internal lints. But this can include enabling some code from the metadata collection monster by default. This mainly involves connecting the configs to the lint documentation and should be relatively simple.

Btw, why does this feature (internal) exists?

I'm not 100% sure, but my guess is a combination of these factors:

• Performance and size, these lints should never detect code outside of Clippy, so they would just waste time and disk space for other projects
• Errors, internal lints are generally less tested than normal lints, which increases the chance of ICEs
• Maybe dependencies?

metadata_collector.rs

The metadata collection monster was the first bigger project I worked on in Clippy/rust-lang. Looking at the code takes me back. I also love how it was okay to have more stupid comments in that code :D

[blyxyas]

@rustbot claim
Done