3 Rustdoc is under active development, and like the Rust compiler, some features are only available
4 on nightly releases. Some of these features are new and need some more testing before they're able to be
5 released to the world at large, and some of them are tied to features in the Rust compiler that are unstable. Several features here require a matching `#![feature(...)]` attribute to
6 enable, and thus are more fully documented in the [Unstable Book]. Those sections will link over
9 [Unstable Book]: ../unstable-book/index.html
11 ## Nightly-gated functionality
13 These features just require a nightly build to operate. Unlike the other features on this page,
14 these don't need to be "turned on" with a command-line flag or a `#![feature(...)]` attribute in
15 your crate. This can give them some subtle fallback modes when used on a stable release, so be
18 ### Error numbers for `compile-fail` doctests
20 As detailed in [the chapter on documentation tests][doctest-attributes], you can add a
21 `compile_fail` attribute to a doctest to state that the test should fail to compile. However, on
22 nightly, you can optionally add an error number to state that a doctest should emit a specific error
25 [doctest-attributes]: write-documentation/documentation-tests.html#attributes
29 extern { fn some_func<T>(x: T); }
33 This is used by the error index to ensure that the samples that correspond to a given error number
34 properly emit that error code. However, these error codes aren't guaranteed to be the only thing
35 that a piece of code emits from version to version, so this is unlikely to be stabilized in the
38 Attempting to use these error numbers on stable will result in the code sample being interpreted as
41 ## Extensions to the `#[doc]` attribute
43 These features operate by extending the `#[doc]` attribute, and thus can be caught by the compiler
44 and enabled with a `#![feature(...)]` attribute in your crate.
46 ### `#[doc(cfg)]`: Recording what platforms or features are required for code to be present
48 * Tracking issue: [#43781](https://github.com/rust-lang/rust/issues/43781)
50 You can use `#[doc(cfg(...))]` to tell Rustdoc exactly which platform items appear on.
53 1. doctests will only run on the appropriate platforms, and
54 2. When Rustdoc renders documentation for that item, it will be accompanied by a banner explaining
55 that the item is only available on certain platforms.
57 `#[doc(cfg)]` is intended to be used alongside [`#[cfg(doc)]`][cfg-doc].
58 For example, `#[cfg(any(windows, doc))]` will preserve the item either on Windows or during the
59 documentation process. Then, adding a new attribute `#[doc(cfg(windows))]` will tell Rustdoc that
60 the item is supposed to be used on Windows. For example:
65 /// Token struct that can only be used on Windows.
66 #[cfg(any(windows, doc))]
68 pub struct WindowsToken;
70 /// Token struct that can only be used on Unix.
71 #[cfg(any(unix, doc))]
75 /// Token struct that is only available with the `serde` feature
76 #[cfg(feature = "serde")]
77 #[doc(cfg(feature = "serde"))]
78 #[derive(serde::Deserialize)]
79 pub struct SerdeToken;
82 In this sample, the tokens will only appear on their respective platforms, but they will both appear
85 `#[doc(cfg(...))]` was introduced to be used by the standard library and currently requires the
86 `#![feature(doc_cfg)]` feature gate. For more information, see [its chapter in the Unstable
87 Book][unstable-doc-cfg] and [its tracking issue][issue-doc-cfg].
89 ### `doc_auto_cfg`: Automatically generate `#[doc(cfg)]`
91 * Tracking issue: [#43781](https://github.com/rust-lang/rust/issues/43781)
93 `doc_auto_cfg` is an extension to the `#[doc(cfg)]` feature. With it, you don't need to add
94 `#[doc(cfg(...)]` anymore unless you want to override the default behaviour. So if we take the
98 #![feature(doc_auto_cfg)]
100 /// Token struct that can only be used on Windows.
101 #[cfg(any(windows, doc))]
102 pub struct WindowsToken;
104 /// Token struct that can only be used on Unix.
105 #[cfg(any(unix, doc))]
106 pub struct UnixToken;
108 /// Token struct that is only available with the `serde` feature
109 #[cfg(feature = "serde")]
110 #[derive(serde::Deserialize)]
111 pub struct SerdeToken;
114 It'll render almost the same, the difference being that `doc` will also be displayed. To fix this,
115 you can use `doc_cfg_hide`:
118 #![feature(doc_cfg_hide)]
119 #![doc(cfg_hide(doc))]
122 And `doc` won't show up anymore!
124 [cfg-doc]: ./advanced-features.md
125 [unstable-doc-cfg]: ../unstable-book/language-features/doc-cfg.html
126 [issue-doc-cfg]: https://github.com/rust-lang/rust/issues/43781
128 ### Adding your trait to the "Notable traits" dialog
130 * Tracking issue: [#45040](https://github.com/rust-lang/rust/issues/45040)
132 Rustdoc keeps a list of a few traits that are believed to be "fundamental" to
133 types that implement them. These traits are intended to be the primary interface
134 for their implementers, and are often most of the API available to be documented
135 on their types. For this reason, Rustdoc will track when a given type implements
136 one of these traits and call special attention to it when a function returns one
137 of these types. This is the "Notable traits" dialog, accessible as a circled `i`
138 button next to the function, which, when clicked, shows the dialog.
140 In the standard library, some of the traits that are part of this list are
141 `Iterator`, `Future`, `io::Read`, and `io::Write`. However, rather than being
142 implemented as a hard-coded list, these traits have a special marker attribute
143 on them: `#[doc(notable_trait)]`. This means that you can apply this attribute
144 to your own trait to include it in the "Notable traits" dialog in documentation.
146 The `#[doc(notable_trait)]` attribute currently requires the `#![feature(doc_notable_trait)]`
147 feature gate. For more information, see [its chapter in the Unstable Book][unstable-notable_trait]
148 and [its tracking issue][issue-notable_trait].
150 [unstable-notable_trait]: ../unstable-book/language-features/doc-notable-trait.html
151 [issue-notable_trait]: https://github.com/rust-lang/rust/issues/45040
153 ### Exclude certain dependencies from documentation
155 * Tracking issue: [#44027](https://github.com/rust-lang/rust/issues/44027)
157 The standard library uses several dependencies which, in turn, use several types and traits from the
158 standard library. In addition, there are several compiler-internal crates that are not considered to
159 be part of the official standard library, and thus would be a distraction to include in
160 documentation. It's not enough to exclude their crate documentation, since information about trait
161 implementations appears on the pages for both the type and the trait, which can be in different
164 To prevent internal types from being included in documentation, the standard library adds an
165 attribute to their `extern crate` declarations: `#[doc(masked)]`. This causes Rustdoc to "mask out"
166 types from these crates when building lists of trait implementations.
168 The `#[doc(masked)]` attribute is intended to be used internally, and requires the
169 `#![feature(doc_masked)]` feature gate. For more information, see [its chapter in the Unstable
170 Book][unstable-masked] and [its tracking issue][issue-masked].
172 [unstable-masked]: ../unstable-book/language-features/doc-masked.html
173 [issue-masked]: https://github.com/rust-lang/rust/issues/44027
175 ### Document primitives
177 This is for Rust compiler internal use only.
179 Since primitive types are defined in the compiler, there's no place to attach documentation
180 attributes. The `#[doc(primitive)]` attribute is used by the standard library to provide a way
181 to generate documentation for primitive types, and requires `#![feature(rustdoc_internals)]` to
184 ### Document keywords
186 This is for Rust compiler internal use only.
188 Rust keywords are documented in the standard library (look for `match` for example).
190 To do so, the `#[doc(keyword = "...")]` attribute is used. Example:
193 #![feature(rustdoc_internals)]
195 /// Some documentation about the keyword.
196 #[doc(keyword = "keyword")]
200 ## Effects of other nightly features
202 These nightly-only features are not primarily related to Rustdoc,
203 but have convenient effects on the documentation produced.
205 ### `fundamental` types
207 Annotating a type with `#[fundamental]` primarily influences coherence rules about generic types,
208 i.e., they alter whether other crates can provide implementations for that type.
209 The unstable book [links to further information][unstable-fundamental].
211 [unstable-fundamental]: https://doc.rust-lang.org/unstable-book/language-features/fundamental.html
213 For documentation, this has an additional side effect:
214 If a method is implemented on `F<T>` (or `F<&T>`),
215 where `F` is a fundamental type,
216 then the method is not only documented at the page about `F`,
217 but also on the page about `T`.
218 In a sense, it makes the type transparent to Rustdoc.
219 This is especially convenient for types that work as annotated pointers,
220 such as `Pin<&mut T>`,
221 as it ensures that methods only implemented through those annotated pointers
222 can still be found with the type they act on.
224 If the `fundamental` feature's effect on coherence is not intended,
225 such a type can be marked as fundamental only for purposes of documentation
226 by introducing a custom feature and
227 limiting the use of `fundamental` to when documentation is built.
229 ## Unstable command-line arguments
231 These features are enabled by passing a command-line flag to Rustdoc, but the flags in question are
232 themselves marked as unstable. To use any of these options, pass `-Z unstable-options` as well as
233 the flag in question to Rustdoc on the command-line. To do this from Cargo, you can either use the
234 `RUSTDOCFLAGS` environment variable or the `cargo rustdoc` command.
236 ### `--markdown-before-content`: include rendered Markdown before the content
238 * Tracking issue: [#44027](https://github.com/rust-lang/rust/issues/44027)
240 Using this flag looks like this:
243 $ rustdoc src/lib.rs -Z unstable-options --markdown-before-content extra.md
244 $ rustdoc README.md -Z unstable-options --markdown-before-content extra.md
247 Just like `--html-before-content`, this allows you to insert extra content inside the `<body>` tag
248 but before the other content `rustdoc` would normally produce in the rendered documentation.
249 However, instead of directly inserting the file verbatim, `rustdoc` will pass the files through a
250 Markdown renderer before inserting the result into the file.
252 ### `--markdown-after-content`: include rendered Markdown after the content
254 Using this flag looks like this:
257 $ rustdoc src/lib.rs -Z unstable-options --markdown-after-content extra.md
258 $ rustdoc README.md -Z unstable-options --markdown-after-content extra.md
261 Just like `--html-after-content`, this allows you to insert extra content before the `</body>` tag
262 but after the other content `rustdoc` would normally produce in the rendered documentation.
263 However, instead of directly inserting the file verbatim, `rustdoc` will pass the files through a
264 Markdown renderer before inserting the result into the file.
266 ### `--playground-url`: control the location of the playground
268 Using this flag looks like this:
271 $ rustdoc src/lib.rs -Z unstable-options --playground-url https://play.rust-lang.org/
274 When rendering a crate's docs, this flag gives the base URL of the Rust Playground, to use for
275 generating `Run` buttons. Unlike `--markdown-playground-url`, this argument works for standalone
276 Markdown files *and* Rust crates. This works the same way as adding `#![doc(html_playground_url =
277 "url")]` to your crate root, as mentioned in [the chapter about the `#[doc]`
278 attribute][doc-playground]. Please be aware that the official Rust Playground at
279 https://play.rust-lang.org does not have every crate available, so if your examples require your
280 crate, make sure the playground you provide has your crate available.
282 [doc-playground]: write-documentation/the-doc-attribute.html#html_playground_url
284 If both `--playground-url` and `--markdown-playground-url` are present when rendering a standalone
285 Markdown file, the URL given to `--markdown-playground-url` will take precedence. If both
286 `--playground-url` and `#![doc(html_playground_url = "url")]` are present when rendering crate docs,
287 the attribute will take precedence.
289 ### `--sort-modules-by-appearance`: control how items on module pages are sorted
291 Using this flag looks like this:
294 $ rustdoc src/lib.rs -Z unstable-options --sort-modules-by-appearance
297 Ordinarily, when `rustdoc` prints items in module pages, it will sort them alphabetically (taking
298 some consideration for their stability, and names that end in a number). Giving this flag to
299 `rustdoc` will disable this sorting and instead make it print the items in the order they appear in
302 ### `--show-type-layout`: add a section to each type's docs describing its memory layout
304 Using this flag looks like this:
307 $ rustdoc src/lib.rs -Z unstable-options --show-type-layout
310 When this flag is passed, rustdoc will add a "Layout" section at the bottom of
311 each type's docs page that includes a summary of the type's memory layout as
312 computed by rustc. For example, rustdoc will show the size in bytes that a value
313 of that type will take in memory.
315 Note that most layout information is **completely unstable** and may even differ
316 between compilations.
318 ### `--resource-suffix`: modifying the name of CSS/JavaScript in crate docs
320 * Tracking issue: [#54765](https://github.com/rust-lang/rust/issues/54765)
322 Using this flag looks like this:
325 $ rustdoc src/lib.rs -Z unstable-options --resource-suffix suf
328 When rendering docs, `rustdoc` creates several CSS and JavaScript files as part of the output. Since
329 all these files are linked from every page, changing where they are can be cumbersome if you need to
330 specially cache them. This flag will rename all these files in the output to include the suffix in
331 the filename. For example, `light.css` would become `light-suf.css` with the above command.
333 ### `--extern-html-root-url`: control how rustdoc links to non-local crates
335 Using this flag looks like this:
338 $ rustdoc src/lib.rs -Z unstable-options --extern-html-root-url some-crate=https://example.com/some-crate/1.0.1
341 Ordinarily, when rustdoc wants to link to a type from a different crate, it looks in two places:
342 docs that already exist in the output directory, or the `#![doc(doc_html_root)]` set in the other
343 crate. However, if you want to link to docs that exist in neither of those places, you can use these
344 flags to control that behavior. When the `--extern-html-root-url` flag is given with a name matching
345 one of your dependencies, rustdoc use that URL for those docs. Keep in mind that if those docs exist
346 in the output directory, those local docs will still override this flag.
348 ### `-Z force-unstable-if-unmarked`
350 Using this flag looks like this:
353 $ rustdoc src/lib.rs -Z force-unstable-if-unmarked
356 This is an internal flag intended for the standard library and compiler that applies an
357 `#[unstable]` attribute to any dependent crate that doesn't have another stability attribute. This
358 allows `rustdoc` to be able to generate documentation for the compiler crates and the standard
359 library, as an equivalent command-line argument is provided to `rustc` when building those crates.
361 ### `--index-page`: provide a top-level landing page for docs
363 This feature allows you to generate an index-page with a given markdown file. A good example of it
364 is the [rust documentation index](https://doc.rust-lang.org/nightly/index.html).
366 With this, you'll have a page which you can custom as much as you want at the top of your crates.
368 Using `index-page` option enables `enable-index-page` option as well.
370 ### `--enable-index-page`: generate a default index page for docs
372 This feature allows the generation of a default index-page which lists the generated crates.
374 ### `--nocapture`: disable output capture for test
376 When this flag is used with `--test`, the output (stdout and stderr) of your tests won't be
377 captured by rustdoc. Instead, the output will be directed to your terminal,
378 as if you had run the test executable manually. This is especially useful
379 for debugging your tests!
381 ### `--check`: only checks the documentation
383 When this flag is supplied, rustdoc will type check and lint your code, but will not generate any
384 documentation or run your doctests.
386 Using this flag looks like:
389 rustdoc -Z unstable-options --check src/lib.rs
392 ### `--static-root-path`: control how static files are loaded in HTML output
394 Using this flag looks like this:
397 $ rustdoc src/lib.rs -Z unstable-options --static-root-path '/cache/'
400 This flag controls how rustdoc links to its static files on HTML pages. If you're hosting a lot of
401 crates' docs generated by the same version of rustdoc, you can use this flag to cache rustdoc's CSS,
402 JavaScript, and font files in a single location, rather than duplicating it once per "doc root"
403 (grouping of crate docs generated into the same output directory, like with `cargo doc`). Per-crate
404 files like the search index will still load from the documentation root, but anything that gets
405 renamed with `--resource-suffix` will load from the given path.
407 ### `--persist-doctests`: persist doctest executables after running
409 * Tracking issue: [#56925](https://github.com/rust-lang/rust/issues/56925)
411 Using this flag looks like this:
414 $ rustdoc src/lib.rs --test -Z unstable-options --persist-doctests target/rustdoctest
417 This flag allows you to keep doctest executables around after they're compiled or run.
418 Usually, rustdoc will immediately discard a compiled doctest after it's been tested, but
419 with this option, you can keep those binaries around for farther testing.
421 ### `--show-coverage`: calculate the percentage of items with documentation
423 * Tracking issue: [#58154](https://github.com/rust-lang/rust/issues/58154)
425 Using this flag looks like this:
428 $ rustdoc src/lib.rs -Z unstable-options --show-coverage
431 It generates something like this:
434 +-------------------------------------+------------+------------+------------+------------+
435 | File | Documented | Percentage | Examples | Percentage |
436 +-------------------------------------+------------+------------+------------+------------+
437 | lib.rs | 4 | 100.0% | 1 | 25.0% |
438 +-------------------------------------+------------+------------+------------+------------+
439 | Total | 4 | 100.0% | 1 | 25.0% |
440 +-------------------------------------+------------+------------+------------+------------+
443 If you want to determine how many items in your crate are documented, pass this flag to rustdoc.
444 When it receives this flag, it will count the public items in your crate that have documentation,
445 and print out the counts and a percentage instead of generating docs.
447 Some methodology notes about what rustdoc counts in this metric:
449 * Rustdoc will only count items from your crate (i.e. items re-exported from other crates don't
451 * Docs written directly onto inherent impl blocks are not counted, even though their doc comments
452 are displayed, because the common pattern in Rust code is to write all inherent methods into the
454 * Items in a trait implementation are not counted, as those impls will inherit any docs from the
456 * By default, only public items are counted. To count private items as well, pass
457 `--document-private-items` at the same time.
459 Public items that are not documented can be seen with the built-in `missing_docs` lint. Private
460 items that are not documented can be seen with Clippy's `missing_docs_in_private_items` lint.
462 Calculating code examples follows these rules:
464 1. These items aren't accounted by default:
470 2. If one of the previously listed items has a code example, then it'll be counted.
474 When using `--output-format json` with this option, it will display the coverage information in
475 JSON format. For example, here is the JSON for a file with one documented item and one
479 /// This item has documentation
482 pub fn no_documentation() {}
486 {"no_std.rs":{"total":3,"with_docs":1,"total_examples":3,"with_examples":0}}
489 Note that the third item is the crate root, which in this case is undocumented.
491 ### `-w`/`--output-format`: output format
493 `--output-format json` emits documentation in the experimental
494 [JSON format](https://doc.rust-lang.org/nightly/nightly-rustc/rustdoc_json_types/). `--output-format html` has no effect,
495 and is also accepted on stable toolchains.
497 JSON Output for toolchain crates (`std`, `alloc`, `core`, `test`, and `proc_macro`)
498 is available via the `rust-docs-json` rustup component.
501 rustup component add --toolchain nightly rust-docs-json
504 Then the json files will be present in the `share/doc/rust/json/` directory
505 of the rustup toolchain directory.
507 It can also be used with `--show-coverage`. Take a look at its
508 [documentation](#--show-coverage-calculate-the-percentage-of-items-with-documentation) for more
511 ### `--enable-per-target-ignores`: allow `ignore-foo` style filters for doctests
513 * Tracking issue: [#64245](https://github.com/rust-lang/rust/issues/64245)
515 Using this flag looks like this:
518 $ rustdoc src/lib.rs -Z unstable-options --enable-per-target-ignores
521 This flag allows you to tag doctests with compiletest style `ignore-foo` filters that prevent
522 rustdoc from running that test if the target triple string contains foo. For example:
525 ///```ignore-foo,ignore-bar
531 This will not be run when the build target is `super-awesome-foo` or `less-bar-awesome`.
532 If the flag is not enabled, then rustdoc will consume the filter, but do nothing with it, and
533 the above example will be run for all targets.
534 If you want to preserve backwards compatibility for older versions of rustdoc, you can use
537 ///```ignore,ignore-foo
543 In older versions, this will be ignored on all targets, but on newer versions `ignore-gnu` will
546 ### `--runtool`, `--runtool-arg`: program to run tests with; args to pass to it
548 * Tracking issue: [#64245](https://github.com/rust-lang/rust/issues/64245)
550 Using these options looks like this:
553 $ rustdoc src/lib.rs -Z unstable-options --runtool runner --runtool-arg --do-thing --runtool-arg --do-other-thing
556 These options can be used to run the doctest under a program, and also pass arguments to
557 that program. For example, if you want to run your doctests under valgrind you might run
560 $ rustdoc src/lib.rs -Z unstable-options --runtool valgrind
563 Another use case would be to run a test inside an emulator, or through a Virtual Machine.
565 ### `--with-examples`: include examples of uses of items as documentation
567 * Tracking issue: [#88791](https://github.com/rust-lang/rust/issues/88791)
569 This option, combined with `--scrape-examples-target-crate` and
570 `--scrape-examples-output-path`, is used to implement the functionality in [RFC
571 #3123](https://github.com/rust-lang/rfcs/pull/3123). Uses of an item (currently
572 functions / call-sites) are found in a crate and its reverse-dependencies, and
573 then the uses are included as documentation for that item. This feature is
574 intended to be used via `cargo doc --scrape-examples`, but the rustdoc-only
578 $ rustdoc examples/ex.rs -Z unstable-options \
579 --extern foobar=target/deps/libfoobar.rmeta \
580 --scrape-examples-target-crate foobar \
581 --scrape-examples-output-path output.calls
582 $ rustdoc src/lib.rs -Z unstable-options --with-examples output.calls
585 First, the library must be checked to generate an `rmeta`. Then a
586 reverse-dependency like `examples/ex.rs` is given to rustdoc with the target
587 crate being documented (`foobar`) and a path to output the calls
588 (`output.calls`). Then, the generated calls file can be passed via
589 `--with-examples` to the subsequent documentation of `foobar`.
591 To scrape examples from test code, e.g. functions marked `#[test]`, then
592 add the `--scrape-tests` flag.
594 ### `--check-cfg`: check configuration flags
596 * Tracking issue: [#82450](https://github.com/rust-lang/rust/issues/82450)
598 This flag accepts the same values as `rustc --check-cfg`, and uses it to check configuration flags.
600 Using this flag looks like this:
603 $ rustdoc src/lib.rs -Z unstable-options \
604 --check-cfg='names()' --check-cfg='values(feature, "foo", "bar")'
607 The example above check every well known names (`target_os`, `doc`, `test`, ... via `names()`)
608 and check the values of `feature`: `foo` and `bar`.
610 ### `--generate-link-to-definition`: Generate links on types in source code
612 * Tracking issue: [#89095](https://github.com/rust-lang/rust/issues/89095)
614 This flag enables the generation of links in the source code pages which allow the reader
615 to jump to a type definition.