Remove html_root_url guideline

Docs.rs has found a way to infer html_root_url for crates and their
dependencies, so manually setting html_root_url is no longer important.

Author: dtolnay

src/checklist.md

@@ -38,7 +38,6 @@
     - authors, description, license, homepage, documentation, repository,
       readme, keywords, categories
   - [ ] Cargo.toml documentation key points to "https://docs.rs/CRATE" ([C-DOCS-RS])
-  - [ ] Crate sets html_root_url attribute "https://docs.rs/CRATE/VER.SI.ON" ([C-HTML-ROOT])
   - [ ] Release notes document all significant changes ([C-RELNOTES])
 - **Predictability** *(crate enables legible code that acts how it looks)*
   - [ ] Smart pointers do not add inherent methods ([C-SMART-PTR])
@@ -106,7 +105,6 @@
 [C-LINK]: documentation.html#c-link
 [C-METADATA]: documentation.html#c-metadata
 [C-DOCS-RS]: documentation.html#c-docs-rs
-[C-HTML-ROOT]: documentation.html#c-html-root
 [C-RELNOTES]: documentation.html#c-relnotes
 
 [C-SMART-PTR]: predictability.html#c-smart-ptr

src/documentation.md

@@ -199,38 +199,6 @@ but should be considered carefully.
 
 [docs.rs]: https://docs.rs
 
-[C-HTML-ROOT]: #c-html-root
-<a id="c-html-root"></a>
-### Crate sets html_root_url attribute (C-HTML-ROOT)
-
-It should point to `"https://docs.rs/CRATE/MAJOR.MINOR.PATCH"`,
-assuming the crate uses docs.rs for its primary API documentation.
-
-The `html_root_url` attribute tells rustdoc how to create URLs to
-items in the crate when compiling downstream crates. Without it, links
-in the documentation of crates that depend on your crate will be
-incorrect.
-
-```rust
-#![doc(html_root_url = "https://docs.rs/log/0.3.8")]
-```
-
-Because this URL contains an exact version number, it must be kept in
-sync with the version number in `Cargo.toml`. The [`version-sync`]
-crate can help with this by letting you add an integration test that
-fails if the `html_root_url` version number is out of sync with the
-crate version.
-
-[`version-sync`]: https://crates.io/crates/version-sync
-
-If you do not like that mechanism, it is recommended to add a comment
-to the `Cargo.toml` version key reminding yourself to keep the two
-updated together, like:
-
-```toml
-version = "0.3.8" # remember to update html_root_url
-```
-
 
 <a id="c-relnotes"></a>
 ## Release notes document all significant changes (C-RELNOTES)