rustdoc: use JS to inline target type impl docs into alias #116471

This is shorter, avoids potential conflicts with a crate named `implementors`[^1], and will be less confusing when JS include files are added for type aliases. [^1]: AFAIK, this couldn't actually cause any problems right now, but it's simpler just to make it impossible than relying on never having a file named `trait.Foo.js` in the crate data area.

This reverts commit c79b960.

This reverts commit c3e5ad4.

This reverts commit d882b21.

This reverts commit b3686c2.

This reverts commit 19edb3c.

This is an attempt to balance three problems, each of which would be violated by a simpler implementation: - A type alias should show all the `impl` blocks for the target type, and vice versa, if they're applicable. If nothing was done, and rustdoc continues to match them up in HIR, this would not work. - Copying the target type's docs into its aliases' HTML pages directly causes far too much redundant HTML text to be generated when a crate has large numbers of methods and large numbers of type aliases. - Using JavaScript exclusively for type alias impl docs would be a functional regression, and could make some docs very hard to find for non-JS readers. - Making sure that only applicable docs are show in the resulting page requires a type checkers. Do not reimplement the type checker in JavaScript. So, to make it work, rustdoc stashes these type-alias-inlined docs in a JSONP "database-lite". The file is generated in `write_shared.rs`, included in a `<script>` tag added in `print_item.rs`, and `main.js` takes care of patching the additional docs into the DOM. The format of `trait.impl` and `type.impl` JS files are superficially similar. Each line, except the JSONP wrapper itself, belongs to a crate, and they are otherwise separate (rustdoc should be idempotent). The "meat" of the file is HTML strings, so the frontend code is very simple. Links are relative to the doc root, though, so the frontend needs to fix that up, and inlined docs can reuse these files. However, there are a few differences, caused by the sophisticated features that type aliases have. Consider this crate graph: ```text --------------------------------- | crate A: struct Foo<T> | | type Bar = Foo<i32> | | impl X for Foo<i8> | | impl Y for Foo<i32> | --------------------------------- | ---------------------------------- | crate B: type Baz = A::Foo<i8> | | type Xyy = A::Foo<i8> | | impl Z for Xyy | ---------------------------------- ``` The type.impl/A/struct.Foo.js JS file has a structure kinda like this: ```js JSONP({ "A": [["impl Y for Foo<i32>", "Y", "A::Bar"]], "B": [["impl X for Foo<i8>", "X", "B::Baz", "B::Xyy"], ["impl Z for Xyy", "Z", "B::Baz"]], }); ``` When the type.impl file is loaded, only the current crate's docs are actually used. The main reason to bundle them together is that there's enough duplication in them for DEFLATE to remove the redundancy. The contents of a crate are a list of impl blocks, themselves represented as lists. The first item in the sublist is the HTML block, the second item is the name of the trait (which goes in the sidebar), and all others are the names of type aliases that successfully match. This way: - There's no need to generate these files for types that have no aliases in the current crate. If a dependent crate makes a type alias, it'll take care of generating its own docs. - There's no need to reimplement parts of the type checker in JavaScript. The Rust backend does the checking, and includes its results in the file. - Docs defined directly on the type alias are dropped directly in the HTML by `render_assoc_items`, and are accessible without JavaScript. The JSONP file will not list impl items that are known to be part of the main HTML file already. [JSONP]: https://en.wikipedia.org/wiki/JSONP

I fixed this in the code, but forgot to fix it in the test.

This line is longer than 100 characters, but apparently, [tidy's list of checked extensions] doesn't include html, so the line length doesn't matter. [tidy's list of checked extensions]: https://github.com/rust-lang/rust/blob/31be8cc41148983e742fea8f559aacca0f6647db/src/tools/tidy/src/style.rs#L245

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rustdoc: use JS to inline target type impl docs into alias #116471

rustdoc: use JS to inline target type impl docs into alias #116471

Commits on Oct 22, 2023