rustdoc links to the wrong method anchor

[jyn514]

I tried this code: laysakura/serde-encrypt@b46c118

I expected to see this happen: All links rustdoc generates are valid.

Instead, this happened: In impl<V: Multilane, T> VZip for T, on encrypt/encrypted_message/struct.EncryptedMessage.html, the function vzip links to #tymethod.vzip, but the proper link is #method.vzip. This causes the anchor to go nowhere.

Meta

rustdoc --version: rustdoc 1.53.0 (53cb7b0 2021-06-17)

This is also present on rustdoc 1.55.0-nightly (7c3872e 2021-06-24).

[jyn514]

searched nightlies: from nightly-2021-04-14 to nightly-2021-04-16
regressed nightly: nightly-2021-04-15
searched commits: from 132b4e5 to 16bf626
regressed commit: b203b0d

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --preserve --start 2021-04-14 --end 2021-04-16 -- deadlinks 

cc @mockersf , do you have time to take a look?

[fee1-dead]

MCVE:

pub trait A {
    fn test();
}

pub struct Foo;

impl A for Foo {
    fn test() {}
}

playground

@rustbot label -E-needs-mcve

[fee1-dead]

Problem is:

rust/src/librustdoc/html/render/mod.rs

Lines 1353 to 1359 in 117799b

	let source_id = trait_
	.and_then(|trait_| {
	trait_.items.iter().find(|item| {
	item.name.map(|n| n.as_str().eq(&name.as_str())).unwrap_or(false)
	})
	})
	.map(|item| format!("{}.{}", item.type_(), name));

Where the item from the trait is used to get source_id. This produces the error because it uses item.type_(), but the type is now TyMethod because it was in a trait. This can be just changed to item_type instead, which refers to the type of the impl method:

rust/src/librustdoc/html/render/mod.rs

Lines 1286 to 1295 in 117799b

	item: &clean::Item,
	parent: &clean::Item,
	containing_item: &clean::Item,
	link: AssocItemLink<'_>,
	render_mode: RenderMode,
	is_default_item: bool,
	trait_: Option<&clean::Trait>,
	show_def_docs: bool,
	) {
	let item_type = item.type_();

To fix this, the suggestion above should be applied and the tests involving this need to be updated.

@rustbot label E-easy

[mockersf]

This seems to happen only for implementations of VZip:
https://docs.rs/serde-encrypt-core/0.6.0/serde_encrypt_core/key/key_pair/public_key/struct.ReceiverPublicKey.html#impl-VZip%3CV%3E
Not sure why, but the trait itself is not a link to the original trait.

It's https://docs.rs/ppv-lite86/0.2.10/ppv_lite86/trait.VZip.html#method.vzip, and on its own page the trait name is not a link in its implementations

The link correctly has a tymethod anchor, but it's missing the page to which it should link to find that anchor. I didn't manage yet to reproduce with a trait that would create the same situation as VZip does