Rustdoc can't create link to trait implementation with generics (`[link](#impl-Trait-for-Type<G1, G2>)`)

[StackOverflowExcept1on]

I tried this code: (bit modified, taken from https://github.com/StackOverflowExcept1on/simple-graph/blob/master/simple-graph/src/graph.rs)

/// ### Serialization to [`String`] in Trivial Graph Format
/// See [`impl<V, E> Display for Graph<V, E>`](#impl-Display-for-Graph<V, E>)
///
/// ### Deserialization from [`&str`] in Trivial Graph Format
/// See [`impl<V, E> FromStr for Graph<V, E>`](#impl-FromStr-for-Graph<V%2C%20E>)

I expected to see this happen: you can create link in rustdoc to #impl-Trait-for-Type<Generic1, Generic2, Generic3, ...>

Instead, this happened: without manually URL-encoding rustdoc can't create link to trait implementation

Fast way to reproduce issue with rustdoc

git clone https://github.com/StackOverflowExcept1on/rustdoc-issue.git
cd rustdoc-issue
cargo doc
firefox target/doc/rustdoc_issue/struct.Type.html

Meta

rustc --version --verbose:

rustc 1.68.0-nightly (bdb07a8ec 2022-12-11)
binary: rustc
commit-hash: bdb07a8ec8e77aa10fb84fae1d4ff71c21180bb4
commit-date: 2022-12-11
host: x86_64-unknown-linux-gnu
release: 1.68.0-nightly
LLVM version: 15.0.6

[fmease]

@rustbot label T-rustdoc A-intra-doc-links

[camelid]

Hmm, I don't think this is a bug. When you use [...](#...) syntax, you're not using intra-doc links; rather, you're creating a manual URL link that you want rustdoc to output as if you'd written an HTML <a href="#...">...</a> tag. It is a limitation of rustdoc that you can't link to individual impls, but I don't think this is a bug.

[StackOverflowExcept1on]

@camelid would be cool to automatically encode URL then. Right now developer need to encode URL manually instead of having readable syntax in the documentation

I think a good solution is

1. re-encode URL anyway (to remove spaces and encode other chars to URL format)
2. try to find tag with this ID <tag id="impl-for-Trait-...-link">...</tag> in rustdoc
3. fallback to existing #link in markdown if we can't find it

[camelid]

Thinking about it again, I am surprised that rustdoc doesn't encode the comma and space in the URL. We should check what the Markdown spec says to do. cc @GuillaumeGomez

[camelid]

Regarding (2) and (3) in your list, I think those would be taken care of by just encoding the URL. Please let me know if I misunderstood.