clippy::let_underscore_lock lint should use #[clippy::has_significant_drop] attribute rather than a hardcoded list

[CAD97]

Description

#[clippy::has_significant_drop] was added for the lint clippy::significant_drop_in_scrutinee.

The clippy::let_underscore_lock currently uses a hardcoded list of type paths to lint against:

rust-clippy/clippy_lints/src/let_underscore.rs

Lines 108 to 114 in a98e7ab

	const SYNC_GUARD_PATHS: [&[&str]; 5] = [
	&paths::MUTEX_GUARD,
	&paths::RWLOCK_READ_GUARD,
	&paths::RWLOCK_WRITE_GUARD,
	&paths::PARKING_LOT_RAWMUTEX,
	&paths::PARKING_LOT_RAWRWLOCK,
	];

Instead, it should use the presence of the new #[clippy::has_significant_drop] attribute.

Checking for the parking_lot types by path might need to stay around for a while until most parking_lot consumers are using a version with the #[clippy::has_significant_drop] attribute.

Version

git master

Additional Labels

@rustbot label +C-enhancement +C-an-interesting-project
(I guess)

[CAD97]

Another mentioned possible heuristic is a #[must_use] type with an explicit Drop implementation.