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| <h1 id="rustdoc-internals"><a class="header" href="#rustdoc-internals">Rustdoc Internals</a></h1> |
| <p>This page describes <a href="https://github.com/rust-lang/rust/tree/master/src/tools/rustdoc"><code>rustdoc</code></a>'s passes and modes. For an overview of <code>rustdoc</code>, |
| see the <a href="./rustdoc.html">"Rustdoc overview" chapter</a>.</p> |
| <h2 id="from-crate-to-clean"><a class="header" href="#from-crate-to-clean">From Crate to Clean</a></h2> |
| <p>In <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/core.rs"><code>core.rs</code></a> are two central items: the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/core/struct.DocContext.html"><code>rustdoc::core::DocContext</code></a> |
| <code>struct</code>, and the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/core/fn.run_global_ctxt.html"><code>rustdoc::core::run_global_ctxt</code></a> function. The latter is |
| where <code>rustdoc</code> calls out to <code>rustc</code> to compile a crate to the point where |
| <code>rustdoc</code> can take over. The former is a state container used when crawling |
| through a crate to gather its documentation.</p> |
| <p>The main process of crate crawling is done in <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/clean/mod.rs"><code>clean/mod.rs</code></a> through several |
| functions with names that start with <code>clean_</code>. Each function accepts an <code>hir</code> |
| or <code>ty</code> data structure, and outputs a <code>clean</code> structure used by <code>rustdoc</code>. For |
| example, <a href="https://doc.rust-lang.org/nightly/nightly-rustc/src/rustdoc/clean/mod.rs.html#256-267">this function for converting lifetimes</a>:</p> |
| <pre><code class="language-rust ignore">fn clean_lifetime<'tcx>(lifetime: &hir::Lifetime, cx: &mut DocContext<'tcx>) -> Lifetime { |
| if let Some( |
| rbv::ResolvedArg::EarlyBound(did) |
| | rbv::ResolvedArg::LateBound(_, _, did) |
| | rbv::ResolvedArg::Free(_, did), |
| ) = cx.tcx.named_bound_var(lifetime.hir_id) |
| && let Some(lt) = cx.args.get(&did).and_then(|arg| arg.as_lt()) |
| { |
| return lt.clone(); |
| } |
| Lifetime(lifetime.ident.name) |
| }</code></pre> |
| <p>Also, <code>clean/mod.rs</code> defines the types for the "cleaned" <a href="./ast-validation.html">Abstract Syntax Tree |
| (<code>AST</code>)</a> used later to render documentation pages. Each usually accompanies a |
| <code>clean_*</code> function that takes some <a href="./ast-validation.html"><code>AST</code></a> or <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/index.html">High-Level Intermediate |
| Representation (<code>HIR</code>)</a> type from <code>rustc</code> and converts it into the |
| appropriate "cleaned" type. "Big" items like modules or associated items may |
| have some extra processing in its <code>clean</code> function, but for the most part these |
| <code>impl</code>s are straightforward conversions. The "entry point" to this module is |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/clean/utils/fn.krate.html#"><code>clean::utils::krate</code></a>, which is called by <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/core/fn.run_global_ctxt.html"><code>run_global_ctxt</code></a>.</p> |
| <p>The first step in <a href="https://doc.rust-lang.org/nightly/nightly-rustc/src/rustdoc/clean/utils.rs.html#31-77"><code>clean::utils::krate</code></a> is to invoke |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/visit_ast/struct.RustdocVisitor.html"><code>visit_ast::RustdocVisitor</code></a> to process the module tree into an intermediate |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/visit_ast/struct.Module.html"><code>visit_ast::Module</code></a>. This is the step that actually crawls the |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/struct.Crate.html"><code>rustc_hir::Crate</code></a>, normalizing various aspects of name resolution, such as:</p> |
| <ul> |
| <li>handling <code>#[doc(inline)]</code> and <code>#[doc(no_inline)]</code></li> |
| <li>handling import globs and cycles, so there are no duplicates or infinite |
| directory trees</li> |
| <li>inlining public <code>use</code> exports of private items, or showing a "Reexport" |
| line in the module page</li> |
| <li>inlining items with <code>#[doc(hidden)]</code> if the base item is hidden but the</li> |
| <li>showing <code>#[macro_export]</code>-ed macros at the crate root, regardless of whether |
| they're defined as a reexport or not</li> |
| </ul> |
| <p>After this step, <code>clean::krate</code> invokes <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/clean/fn.clean_doc_module.html"><code>clean_doc_module</code></a>, which actually |
| converts the <code>HIR</code> items to the cleaned <a href="./ast-validation.html"><code>AST</code></a>. This is also the step where cross- |
| crate inlining is performed, which requires converting <code>rustc_middle</code> data |
| structures into the cleaned <a href="./ast-validation.html"><code>AST</code></a>.</p> |
| <p>The other major thing that happens in <code>clean/mod.rs</code> is the collection of doc |
| comments and <code>#[doc=""]</code> attributes into a separate field of the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/clean/types/struct.Attributes.html"><code>Attributes</code></a> |
| <code>struct</code>, present on anything that gets hand-written documentation. This makes it |
| easier to collect this documentation later in the process.</p> |
| <p>The primary output of this process is a <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/clean/types/struct.Crate.html"><code>clean::types::Crate</code></a> with a tree of <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/clean/types/struct.Item.html"><code>Item</code></a>s |
| which describe the publicly-documentable items in the target crate.</p> |
| <h3 id="passes-anything-but-a-gas-station-or-hot-potato"><a class="header" href="#passes-anything-but-a-gas-station-or-hot-potato">Passes Anything But a Gas Station (or: <a href="https://www.youtube.com/watch?v=WNFBIt5HxdY">Hot Potato</a>)</a></h3> |
| <p>Before moving on to the next major step, a few important "passes" occur over |
| the cleaned <a href="./ast-validation.html"><code>AST</code></a>. Several of these passes are <code>lint</code>s and reports, but some of |
| them mutate or generate new items.</p> |
| <p>These are all implemented in the <a href="https://github.com/rust-lang/rust/tree/master/src/librustdoc/passes"><code>librustdoc/passes</code></a> 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 |
| <code>--document-private-items</code> to <code>rustdoc</code>. Note that unlike the previous set of <a href="./ast-validation.html"><code>AST</code></a> |
| transformations, the passes are run on the <em>cleaned</em> crate.</p> |
| <p>Here is the list of passes as of <!-- date-check --> March 2023:</p> |
| <ul> |
| <li> |
| <p><code>calculate-doc-coverage</code> calculates information used for the <code>--show-coverage</code> |
| flag.</p> |
| </li> |
| <li> |
| <p><code>check-doc-test-visibility</code> runs <code>doctest</code> visibility–related <code>lint</code>s. This pass |
| runs before <code>strip-private</code>, which is why it needs to be separate from |
| <code>run-lints</code>.</p> |
| </li> |
| <li> |
| <p><code>collect-intra-doc-links</code> resolves <a href="https://doc.rust-lang.org/nightly/rustdoc/write-documentation/linking-to-items-by-name.html">intra-doc links</a>.</p> |
| </li> |
| <li> |
| <p><code>collect-trait-impls</code> collects <code>trait</code> <code>impl</code>s for each item in the crate. For |
| example, if we define a <code>struct</code> that implements a <code>trait</code>, this pass will note |
| that the <code>struct</code> implements that <code>trait</code>.</p> |
| </li> |
| <li> |
| <p><code>propagate-doc-cfg</code> propagates <code>#[doc(cfg(...))]</code> to child items.</p> |
| </li> |
| <li> |
| <p><code>run-lints</code> runs some of <code>rustdoc</code>'s <code>lint</code>s, defined in <code>passes/lint</code>. This is |
| the last pass to run.</p> |
| <ul> |
| <li> |
| <p><code>bare_urls</code> detects links that are not linkified, e.g., in Markdown such as |
| <code>Go to https://example.com/.</code> It suggests wrapping the link with angle brackets: |
| <code>Go to <https://example.com/>.</code> to linkify it. This is the code behind the <!-- |
| date-check: may 2022 --> <code>rustdoc::bare_urls</code> <code>lint</code>.</p> |
| </li> |
| <li> |
| <p><code>check_code_block_syntax</code> validates syntax inside Rust code blocks |
| (<code>```rust</code>)</p> |
| </li> |
| <li> |
| <p><code>html_tags</code> detects invalid <code>HTML</code> (like an unclosed <code><span></code>) |
| in doc comments.</p> |
| </li> |
| </ul> |
| </li> |
| <li> |
| <p><code>strip-hidden</code> and <code>strip-private</code> strip all <code>doc(hidden)</code> and private items |
| from the output. <code>strip-private</code> implies <code>strip-priv-imports</code>. Basically, the |
| goal is to remove items that are not relevant for public documentation. This |
| pass is skipped when <code>--document-hidden-items</code> is passed.</p> |
| </li> |
| <li> |
| <p><code>strip-priv-imports</code> strips all private import statements (<code>use</code>, <code>extern crate</code>) from a crate. This is necessary because <code>rustdoc</code> will handle <em>public</em> |
| imports by either inlining the item's documentation to the module or creating |
| a "Reexports" section with the import in it. The pass ensures that all of |
| these imports are actually relevant to documentation. It is technically |
| only run when <code>--document-private-items</code> is passed, but <code>strip-private</code> |
| accomplishes the same thing.</p> |
| </li> |
| <li> |
| <p><code>strip-private</code> strips all private items from a crate which cannot be seen |
| externally. This pass is skipped when <code>--document-private-items</code> is passed.</p> |
| </li> |
| </ul> |
| <p>There is also a <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/passes/stripper/index.html"><code>stripper</code></a> module in <code>librustdoc/passes</code>, but it is a |
| collection of utility functions for the <code>strip-*</code> passes and is not a pass |
| itself.</p> |
| <h2 id="from-clean-to-html"><a class="header" href="#from-clean-to-html">From Clean To HTML</a></h2> |
| <p>This is where the "second phase" in <code>rustdoc</code> begins. This phase primarily lives |
| in the <a href="https://github.com/rust-lang/rust/tree/master/src/librustdoc/formats"><code>librustdoc/formats</code></a> and <a href="https://github.com/rust-lang/rust/tree/master/src/librustdoc/html"><code>librustdoc/html</code></a> folders, and it all starts with |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/formats/renderer/fn.run_format.html"><code>formats::renderer::run_format</code></a>. This code is responsible for setting up a type that |
| <code>impl FormatRenderer</code>, which for <code>HTML</code> is <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/html/render/context/struct.Context.html"><code>Context</code></a>.</p> |
| <p>This structure contains methods that get called by <code>run_format</code> to drive the |
| doc rendering, which includes:</p> |
| <ul> |
| <li><code>init</code> generates <code>static.files</code>, as well as search index and <code>src/</code></li> |
| <li><code>item</code> generates the item <code>HTML</code> files themselves</li> |
| <li><code>after_krate</code> generates other global resources like <code>all.html</code></li> |
| </ul> |
| <p>In <code>item</code>, the "page rendering" occurs, via a mixture of <a href="https://docs.rs/askama/latest/askama/">Askama</a> templates |
| and manual <code>write!()</code> calls, starting in <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/layout.rs"><code>html/layout.rs</code></a>. The parts that have |
| not been converted to templates occur within a series of <code>std::fmt::Display</code> |
| implementations and functions that pass around a <code>&mut std::fmt::Formatter</code>.</p> |
| <p>The parts that actually generate <code>HTML</code> from the items and documentation start |
| with <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/html/render/print_item/fn.print_item.html"><code>print_item</code></a> defined in <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/render/print_item.rs"><code>html/render/print_item.rs</code></a>, which switches out |
| to one of several <code>item_*</code> functions based on kind of <code>Item</code> being rendered.</p> |
| <p>Depending on what kind of rendering code you're looking for, you'll probably |
| find it either in <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/render/mod.rs"><code>html/render/mod.rs</code></a> for major items like "what sections |
| should I print for a <code>struct</code> page" or <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/format.rs"><code>html/format.rs</code></a> for smaller component |
| pieces like "how should I print a where clause as part of some other item".</p> |
| <p>Whenever <code>rustdoc</code> comes across an item that should print hand-written |
| documentation alongside, it calls out to <a href="https://github.com/rust-lang/rust/blob/master/src/librustdoc/html/markdown.rs"><code>html/markdown.rs</code></a> which interfaces |
| with the Markdown parser. This is exposed as a series of types that wrap a |
| string of Markdown, and implement <code>fmt::Display</code> to emit <code>HTML</code> text. It takes |
| special care to enable certain features like footnotes and tables and add |
| syntax highlighting to Rust code blocks (via <code>html/highlight.rs</code>) before |
| running the Markdown parser. There's also a function <a href="https://doc.rust-lang.org/nightly/nightly-rustc/src/rustdoc/html/markdown.rs.html#749-818"><code>find_codes</code></a> which is |
| called by <code>find_testable_codes</code> that specifically scans for Rust code blocks so |
| the test-runner code can find all the <code>doctest</code>s in the crate.</p> |
| <h3 id="from-soup-to-nuts-or-an-unbroken-thread-stretches-from-those-first-cells-to-us"><a class="header" href="#from-soup-to-nuts-or-an-unbroken-thread-stretches-from-those-first-cells-to-us">From Soup to Nuts (or: <a href="https://www.youtube.com/watch?v=hOLAGYmUQV0">"An Unbroken Thread Stretches From Those First <code>Cell</code>s To Us"</a>)</a></h3> |
| <p>It's important to note that <code>rustdoc</code> can ask the compiler for type information |
| directly, even during <code>HTML</code> generation. This <a href="https://github.com/rust-lang/rust/pull/80090">didn't used to be the case</a>, and |
| a lot of <code>rustdoc</code>'s architecture was designed around not doing that, but a |
| <code>TyCtxt</code> is now passed to <code>formats::renderer::run_format</code>, which is used to |
| run generation for both <code>HTML</code> and the |
| (unstable as of <!-- date-check --> March 2023) JSON format.</p> |
| <p>This change has allowed other changes to remove data from the "clean" <a href="./ast-validation.html"><code>AST</code></a> |
| that can be easily derived from <code>TyCtxt</code> queries, and we'll usually accept |
| PRs that remove fields from "clean" (it's been soft-deprecated), but this |
| is complicated from two other constraints that <code>rustdoc</code> runs under:</p> |
| <ul> |
| <li>Docs can be generated for crates that don't actually pass type checking. |
| This is used for generating docs that cover mutually-exclusive platform |
| configurations, such as <code>libstd</code> having a single package of docs that |
| cover all supported operating systems. This means <code>rustdoc</code> has to be able |
| to generate docs from <code>HIR</code>.</li> |
| <li>Docs can inline across crates. Since crate metadata doesn't contain <code>HIR</code>, |
| it must be possible to generate inlined docs from the <code>rustc_middle</code> data.</li> |
| </ul> |
| <p>The "clean" <a href="./ast-validation.html"><code>AST</code></a> acts as a common output format for both input formats. There |
| is also some data in clean that doesn't correspond directly to <code>HIR</code>, such as |
| synthetic <code>impl</code>s for auto traits and blanket <code>impl</code>s generated by the |
| <code>collect-trait-impls</code> pass.</p> |
| <p>Some additional data is stored in |
| <code>html::render::context::{Context, SharedContext}</code>. These two types serve as |
| ways to segregate <code>rustdoc</code>'s data for an eventual future with multithreaded doc |
| generation, as well as just keeping things organized:</p> |
| <ul> |
| <li><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/html/render/context/struct.Context.html"><code>Context</code></a> stores data used for generating the current page, such as its |
| path, a list of <code>HTML</code> IDs that have been used (to avoid duplicate <code>id=""</code>), |
| and the pointer to <code>SharedContext</code>.</li> |
| <li><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/html/render/context/struct.SharedContext.html"><code>SharedContext</code></a> stores data that does not vary by page, such as the <code>tcx</code> |
| pointer, and a list of all types.</li> |
| </ul> |
| <h2 id="other-tricks-up-its-sleeve"><a class="header" href="#other-tricks-up-its-sleeve">Other Tricks Up Its Sleeve</a></h2> |
| <p>All this describes the process for generating <code>HTML</code> documentation from a Rust |
| crate, but there are couple other major modes that <code>rustdoc</code> runs in. It can also |
| be run on a standalone Markdown file, or it can run <code>doctest</code>s on Rust code or |
| standalone Markdown files. For the former, it shortcuts straight to |
| <code>html/markdown.rs</code>, optionally including a mode which inserts a Table of |
| Contents to the output <code>HTML</code>.</p> |
| <p>For the latter, <code>rustdoc</code> runs a similar partial-compilation to get relevant |
| documentation in <code>test.rs</code>, but instead of going through the full clean and |
| render process, it runs a much simpler crate walk to grab <em>just</em> the |
| hand-written documentation. Combined with the aforementioned |
| "<code>find_testable_code</code>" in <code>html/markdown.rs</code>, it builds up a collection of |
| tests to run before handing them off to the test runner. One notable location |
| in <code>test.rs</code> is the function <code>make_test</code>, which is where hand-written |
| <code>doctest</code>s get transformed into something that can be executed.</p> |
| <p>Some extra reading about <code>make_test</code> can be found |
| <a href="https://quietmisdreavus.net/code/2018/02/23/how-the-doctests-get-made/">here</a>.</p> |
| <h2 id="testing-locally"><a class="header" href="#testing-locally">Testing Locally</a></h2> |
| <p>Some features of the generated <code>HTML</code> documentation might require local |
| storage to be used across pages, which doesn't work well without an <code>HTTP</code> |
| server. To test these features locally, you can run a local <code>HTTP</code> server, like |
| this:</p> |
| <pre><code class="language-bash">$ ./x doc library |
| # The documentation has been generated into `build/[YOUR ARCH]/doc`. |
| $ python3 -m http.server -d build/[YOUR ARCH]/doc |
| </code></pre> |
| <p>Now you can browse your documentation just like you would if it was hosted |
| on the internet. For example, the url for <code>std</code> will be <code>rust/std/</code>.</p> |
| <h2 id="see-also"><a class="header" href="#see-also">See Also</a></h2> |
| <ul> |
| <li>The <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc/"><code>rustdoc</code> api docs</a></li> |
| <li><a href="./rustdoc.html">An overview of <code>rustdoc</code></a></li> |
| <li><a href="https://doc.rust-lang.org/nightly/rustdoc/">The rustdoc user guide</a></li> |
| </ul> |
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