mem_replace_with_default: recognize some std library ctors

[mgacek8]

fixes #6562
changelog: mem_replace_with_default: recognize some common constructors equivalent to Default::default()

[rust-highfive]

r? @phansch

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[camsteffen]

Suggested change

	paths::BINARY_HEAP_NEW.as_ref(),
	(sym::BinaryHeap, sym::new),

All of these types will have diagnostic items after the next sync with rustc so we should probably use those instead of adding more paths. You can use the util function is_diagnostic_assoc_item instead of match_def_path.

[mgacek8]

I wasn't aware of it, thanks! Makes sense to me to wait then.
I got a question related to this:

• For Default trait, won't we need default_trait symbol specified (similar to e.g. debug_trait)? It is not defined for the Default trait. Or maybe Default symbol is sufficient?

[camsteffen]

Oh that one needs to be added. Or use the current method for now. The symbol needed just depends on what the diagnostic item is named in #[rustc_diagnostic_item = "name"]. Personally I like naming it the same as the item like Default.

[mgacek8]

I see that the name we need to use comes from #[rustc_diagnostic_item = "name"], but by that:

Or maybe Default symbol is sufficient?

I meant already defined Default symbol in symbol.rs. I don't quite understand what it is then (because #[rustc_diagnostic_item="..." is not defined for the Default trait)

[camsteffen]

A Symbol is just an interned string. So if we add #[rustc_diagnostic_item="Default"] and Default is already in symbol.rs then we don't need to add to symbol.rs. We also could use sym!(Default) which expands to Symbol::intern("Default"). But having sym::Default is better because it is const. I hope that answers your question?

[mgacek8]

Now it is more clear, thanks!
Created this PR in rust repo to add diagnostic item to Default trait.

[bors]

☔ The latest upstream changes (presumably #6823) made this pull request unmergeable. Please resolve the merge conflicts.

[phansch]

Marking this as S-blocked until we did the sync

[phansch]

Hi @mgacek8, the Rustup landed so the diagnostic item for the Default trait should be available in Clippy now =)

[phansch]

@bors r+ thanks!

[bors]

📌 Commit 41be515 has been approved by phansch

[bors]

⌛ Testing commit 41be515 with merge 92b9677...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: phansch
Pushing 92b9677 to master...