From 0ca9a4c55b16761d3fd6ee5d305f15c4270b78e7 Mon Sep 17 00:00:00 2001 From: Mark Mansi Date: Mon, 12 Mar 2018 20:09:50 -0500 Subject: [PATCH] Move librustdoc readme to rustc guide --- src/librustdoc/README.md | 173 +-------------------------------------- 1 file changed, 2 insertions(+), 171 deletions(-) diff --git a/src/librustdoc/README.md b/src/librustdoc/README.md index b0a5ae3718df3..2cfe43a8389bb 100644 --- a/src/librustdoc/README.md +++ b/src/librustdoc/README.md @@ -1,172 +1,3 @@ -# The walking tour of rustdoc +For more information about how `librustdoc` works, see the [rustc guide]. -Rustdoc is implemented entirely within the crate `librustdoc`. After partially compiling a crate to -get its AST (technically the HIR map) from rustc, librustdoc performs two major steps past that to -render a set of documentation: - -* "Clean" the AST into a form that's more suited to creating documentation (and slightly more - resistant to churn in the compiler). -* Use this cleaned AST to render a crate's documentation, one page at a time. - -Naturally, there's more than just this, and those descriptions simplify out lots of details, but -that's the high-level overview. - -(Side note: this is a library crate! The `rustdoc` binary is crated using the project in -`src/tools/rustdoc`. Note that literally all that does is call the `main()` that's in this crate's -`lib.rs`, though.) - -## Cheat sheet - -* Use `x.py build --stage 1 src/libstd src/tools/rustdoc` to make a useable rustdoc you can run on - other projects. - * Add `src/libtest` to be able to use `rustdoc --test`. - * If you've used `rustup toolchain link local /path/to/build/$TARGET/stage1` previously, then - after the previous build command, `cargo +local doc` will Just Work. -* Use `x.py doc --stage 1 src/libstd` to use this rustdoc to generate the standard library docs. - * The completed docs will be available in `build/$TARGET/doc/std`, though the bundle is meant to - be used as though you would copy out the `doc` folder to a web server, since that's where the - CSS/JS and landing page are. -* Most of the HTML printing code is in `html/format.rs` and `html/render.rs`. It's in a bunch of - `fmt::Display` implementations and supplementary functions. -* The types that got `Display` impls above are defined in `clean/mod.rs`, right next to the custom - `Clean` trait used to process them out of the rustc HIR. -* The bits specific to using rustdoc as a test harness are in `test.rs`. -* The Markdown renderer is loaded up in `html/markdown.rs`, including functions for extracting - doctests from a given block of Markdown. -* The tests on rustdoc *output* are located in `src/test/rustdoc`, where they're handled by the test - runner of rustbuild and the supplementary script `src/etc/htmldocck.py`. -* Tests on search index generation are located in `src/test/rustdoc-js`, as a series of JavaScript - files that encode queries on the standard library search index and expected results. - -## From crate to clean - -In `core.rs` are two central items: the `DocContext` struct, and the `run_core` function. The latter -is where rustdoc calls out to rustc to compile a crate to the point where rustdoc can take over. The -former is a state container used when crawling through a crate to gather its documentation. - -The main process of crate crawling is done in `clean/mod.rs` through several implementations of the -`Clean` trait defined within. This is a conversion trait, which defines one method: - -```rust -pub trait Clean { - fn clean(&self, cx: &DocContext) -> T; -} -``` - -`clean/mod.rs` also defines the types for the "cleaned" AST used later on to render documentation -pages. Each usually accompanies an implementation of `Clean` that takes some AST or HIR type from -rustc and converts it into the appropriate "cleaned" type. "Big" items like modules or associated -items may have some extra processing in its `Clean` implementation, but for the most part these -impls are straightforward conversions. The "entry point" to this module is the `impl Clean -for visit_ast::RustdocVisitor`, which is called by `run_core` above. - -You see, I actually lied a little earlier: There's another AST transformation that happens before -the events in `clean/mod.rs`. In `visit_ast.rs` is the type `RustdocVisitor`, which *actually* -crawls a `hir::Crate` to get the first intermediate representation, defined in `doctree.rs`. This -pass is mainly to get a few intermediate wrappers around the HIR types and to process visibility -and inlining. This is where `#[doc(inline)]`, `#[doc(no_inline)]`, and `#[doc(hidden)]` are -processed, as well as the logic for whether a `pub use` should get the full page or a "Reexport" -line in the module page. - -The other major thing that happens in `clean/mod.rs` is the collection of doc comments and -`#[doc=""]` attributes into a separate field of the Attributes struct, present on anything that gets -hand-written documentation. This makes it easier to collect this documentation later in the process. - -The primary output of this process is a clean::Crate with a tree of Items which describe the -publicly-documentable items in the target crate. - -### Hot potato - -Before moving on to the next major step, a few important "passes" occur over the documentation. -These do things like combine the separate "attributes" into a single string and strip leading -whitespace to make the document easier on the markdown parser, or drop items that are not public or -deliberately hidden with `#[doc(hidden)]`. These are all implemented in the `passes/` directory, one -file per pass. By default, all of these passes are run on a crate, but the ones regarding dropping -private/hidden items can be bypassed by passing `--document-private-items` to rustdoc. - -(Strictly speaking, you can fine-tune the passes run and even add your own, but [we're trying to -deprecate that][44136]. If you need finer-grain control over these passes, please let us know!) - -[44136]: https://github.com/rust-lang/rust/issues/44136 - -## From clean to crate - -This is where the "second phase" in rustdoc begins. This phase primarily lives in the `html/` -folder, and it all starts with `run()` in `html/render.rs`. This code is responsible for setting up -the `Context`, `SharedContext`, and `Cache` which are used during rendering, copying out the static -files which live in every rendered set of documentation (things like the fonts, CSS, and JavaScript -that live in `html/static/`), creating the search index, and printing out the source code rendering, -before beginning the process of rendering all the documentation for the crate. - -Several functions implemented directly on `Context` take the `clean::Crate` and set up some state -between rendering items or recursing on a module's child items. From here the "page rendering" -begins, via an enormous `write!()` call in `html/layout.rs`. The parts that actually generate HTML -from the items and documentation occurs within a series of `std::fmt::Display` implementations and -functions that pass around a `&mut std::fmt::Formatter`. The top-level implementation that writes -out the page body is the `impl<'a> fmt::Display for Item<'a>` in `html/render.rs`, which switches -out to one of several `item_*` functions based on the kind of `Item` being rendered. - -Depending on what kind of rendering code you're looking for, you'll probably find it either in -`html/render.rs` for major items like "what sections should I print for a struct page" or -`html/format.rs` for smaller component pieces like "how should I print a where clause as part of -some other item". - -Whenever rustdoc comes across an item that should print hand-written documentation alongside, it -calls out to `html/markdown.rs` which interfaces with the Markdown parser. This is exposed as a -series of types that wrap a string of Markdown, and implement `fmt::Display` to emit HTML text. It -takes special care to enable certain features like footnotes and tables and add syntax highlighting -to Rust code blocks (via `html/highlight.rs`) before running the Markdown parser. There's also a -function in here (`find_testable_code`) that specifically scans for Rust code blocks so the -test-runner code can find all the doctests in the crate. - -### From soup to nuts - -(alternate title: ["An unbroken thread that stretches from those first `Cell`s to us"][video]) - -[video]: https://www.youtube.com/watch?v=hOLAGYmUQV0 - -It's important to note that the AST cleaning can ask the compiler for information (crucially, -`DocContext` contains a `TyCtxt`), but page rendering cannot. The `clean::Crate` created within -`run_core` is passed outside the compiler context before being handed to `html::render::run`. This -means that a lot of the "supplementary data" that isn't immediately available inside an item's -definition, like which trait is the `Deref` trait used by the language, needs to be collected during -cleaning, stored in the `DocContext`, and passed along to the `SharedContext` during HTML rendering. -This manifests as a bunch of shared state, context variables, and `RefCell`s. - -Also of note is that some items that come from "asking the compiler" don't go directly into the -`DocContext` - for example, when loading items from a foreign crate, rustdoc will ask about trait -implementations and generate new `Item`s for the impls based on that information. This goes directly -into the returned `Crate` rather than roundabout through the `DocContext`. This way, these -implementations can be collected alongside the others, right before rendering the HTML. - -## Other tricks up its sleeve - -All this describes the process for generating HTML documentation from a Rust crate, but there are -couple other major modes that rustdoc runs in. It can also be run on a standalone Markdown file, or -it can run doctests on Rust code or standalone Markdown files. For the former, it shortcuts straight -to `html/markdown.rs`, optionally including a mode which inserts a Table of Contents to the output -HTML. - -For the latter, rustdoc runs a similar partial-compilation to get relevant documentation in -`test.rs`, but instead of going through the full clean and render process, it runs a much simpler -crate walk to grab *just* the hand-written documentation. Combined with the aforementioned -"`find_testable_code`" in `html/markdown.rs`, it builds up a collection of tests to run before -handing them off to the libtest test runner. One notable location in `test.rs` is the function -`make_test`, which is where hand-written doctests get transformed into something that can be -executed. - -## Dotting i's and crossing t's - -So that's rustdoc's code in a nutshell, but there's more things in the repo that deal with it. Since -we have the full `compiletest` suite at hand, there's a set of tests in `src/test/rustdoc` that make -sure the final HTML is what we expect in various situations. These tests also use a supplementary -script, `src/etc/htmldocck.py`, that allows it to look through the final HTML using XPath notation -to get a precise look at the output. The full description of all the commands available to rustdoc -tests is in `htmldocck.py`. - -In addition, there are separate tests for the search index and rustdoc's ability to query it. The -files in `src/test/rustdoc-js` each contain a different search query and the expected results, -broken out by search tab. These files are processed by a script in `src/tools/rustdoc-js` and the -Node.js runtime. These tests don't have as thorough of a writeup, but a broad example that features -results in all tabs can be found in `basic.js`. The basic idea is that you match a given `QUERY` -with a set of `EXPECTED` results, complete with the full item path of each item. +[rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/rustdoc.html