| # Comments |
| |
| > **<sup>Lexer</sup>**\ |
| > LINE_COMMENT :\ |
| > `//` (~\[`/` `!` `\n`] | `//`) ~`\n`<sup>\*</sup>\ |
| > | `//` |
| > |
| > BLOCK_COMMENT :\ |
| > `/*` (~\[`*` `!`] | `**` | _BlockCommentOrDoc_) |
| > (_BlockCommentOrDoc_ | ~`*/`)<sup>\*</sup> `*/`\ |
| > | `/**/`\ |
| > | `/***/` |
| > |
| > INNER_LINE_DOC :\ |
| > `//!` ~\[`\n` _IsolatedCR_]<sup>\*</sup> |
| > |
| > INNER_BLOCK_DOC :\ |
| > `/*!` ( _BlockCommentOrDoc_ | ~\[`*/` _IsolatedCR_] )<sup>\*</sup> `*/` |
| > |
| > OUTER_LINE_DOC :\ |
| > `///` (~`/` ~\[`\n` _IsolatedCR_]<sup>\*</sup>)<sup>?</sup> |
| > |
| > OUTER_BLOCK_DOC :\ |
| > `/**` (~`*` | _BlockCommentOrDoc_ ) |
| > (_BlockCommentOrDoc_ | ~\[`*/` _IsolatedCR_])<sup>\*</sup> `*/` |
| > |
| > _BlockCommentOrDoc_ :\ |
| > BLOCK_COMMENT\ |
| > | OUTER_BLOCK_DOC\ |
| > | INNER_BLOCK_DOC |
| > |
| > _IsolatedCR_ :\ |
| > \\r |
| |
| ## Non-doc comments |
| |
| Comments follow the general C++ style of line (`//`) and |
| block (`/* ... */`) comment forms. Nested block comments are supported. |
| |
| Non-doc comments are interpreted as a form of whitespace. |
| |
| ## Doc comments |
| |
| Line doc comments beginning with exactly _three_ slashes (`///`), and block |
| doc comments (`/** ... */`), both outer doc comments, are interpreted as a |
| special syntax for [`doc` attributes]. That is, they are equivalent to writing |
| `#[doc="..."]` around the body of the comment, i.e., `/// Foo` turns into |
| `#[doc="Foo"]` and `/** Bar */` turns into `#[doc="Bar"]`. |
| |
| Line comments beginning with `//!` and block comments `/*! ... */` are |
| doc comments that apply to the parent of the comment, rather than the item |
| that follows. That is, they are equivalent to writing `#![doc="..."]` around |
| the body of the comment. `//!` comments are usually used to document |
| modules that occupy a source file. |
| |
| The character `U+000D` (CR) is not allowed in doc comments. |
| |
| > **Note**: The sequence `U+000D` (CR) immediately followed by `U+000A` (LF) would have been previously transformed into a single `U+000A` (LF). |
| |
| ## Examples |
| |
| ```rust |
| //! A doc comment that applies to the implicit anonymous module of this crate |
| |
| pub mod outer_module { |
| |
| //! - Inner line doc |
| //!! - Still an inner line doc (but with a bang at the beginning) |
| |
| /*! - Inner block doc */ |
| /*!! - Still an inner block doc (but with a bang at the beginning) */ |
| |
| // - Only a comment |
| /// - Outer line doc (exactly 3 slashes) |
| //// - Only a comment |
| |
| /* - Only a comment */ |
| /** - Outer block doc (exactly) 2 asterisks */ |
| /*** - Only a comment */ |
| |
| pub mod inner_module {} |
| |
| pub mod nested_comments { |
| /* In Rust /* we can /* nest comments */ */ */ |
| |
| // All three types of block comments can contain or be nested inside |
| // any other type: |
| |
| /* /* */ /** */ /*! */ */ |
| /*! /* */ /** */ /*! */ */ |
| /** /* */ /** */ /*! */ */ |
| pub mod dummy_item {} |
| } |
| |
| pub mod degenerate_cases { |
| // empty inner line doc |
| //! |
| |
| // empty inner block doc |
| /*!*/ |
| |
| // empty line comment |
| // |
| |
| // empty outer line doc |
| /// |
| |
| // empty block comment |
| /**/ |
| |
| pub mod dummy_item {} |
| |
| // empty 2-asterisk block isn't a doc block, it is a block comment |
| /***/ |
| |
| } |
| |
| /* The next one isn't allowed because outer doc comments |
| require an item that will receive the doc */ |
| |
| /// Where is my item? |
| # mod boo {} |
| } |
| ``` |
| |
| [`doc` attributes]: ../rustdoc/the-doc-attribute.html |
