feat: make trait assoc items become inactive due to cfg

[kartva]

fixes #12394

[kartva]

Narrowed down the logic for ignoring the assoc items to

rust-analyzer/crates/hir-def/src/data.rs

Lines 475 to 484 in 1883d1f

	fn collect(&mut self, item_tree: &ItemTree, tree_id: TreeId, assoc_items: &[AssocItem]) {
	let container = self.container;
	self.items.reserve(assoc_items.len());
	'items: for &item in assoc_items {
	let attrs = item_tree.attrs(self.db, self.module_id.krate, ModItem::from(item).into());
	if !attrs.is_cfg_enabled(self.expander.cfg_options()) {
	continue;
	}

[kartva]

Searching for is_cfg_enabled is the way to go for finding places where things are filtered without emitting a diagnostic.

[kartva]

@flodiebold
For the plumbing you mentioned, most sub-items are filtered in hir-def/src/adt, while inactive diagnostics are emitted in hir-def/src/nameres/collector (for inactive module items). Additionally, the diagnostics structs are only available to modules in the nameres module. I saw #8973 which moved diagnostics to its current position.

Should I try to thread a diagnostics vec for all the functions that filter cfg'd fields? Is there a particular reason why fields are filtered at the AST stage, instead of the HIR stage like module items?

[kartva]

Discussion on Zulip

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit 23c00ed has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 23c00ed with merge dea1639...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing dea1639 to master...

[lnicola]