How to link to other fns/structs/enums/traits in rustdoc? - rust

I'm building a Rust library and want to give it some polish. In the rustdoc, I'd sometimes like to link to other parts of the library within the docs, e.g. fns, traits or structs. What is the official syntax for this?

As of Rust 1.48, you can now rely on RFC 1946. This adds the concept of intra-documentation links. This allows using Rust paths as the URL of a link:
[Iterator](std::iter::Iterator)
[Iterator][iter], and somewhere else in the document: [iter]: std::iter::Iterator
[Iterator], and somewhere else in the document: [Iterator]: std::iter::Iterator
The RFC also introduces "Implied Shortcut Reference Links". This allows leaving out the link reference, which is then inferred automatically.
[std::iter::Iterator], without having a link reference definition for Iterator anywhere else in the document
[`std::iter::Iterator`], without having a link reference definition for Iterator anywhere else in the document (same as previous style but with back ticks to format link as inline code)
As a concrete example, this source code:
//! Check out [ExampleStruct], especially [this
//! method](ExampleStruct::foo), but [the trait method][trait] is also
//! cool. There is also [an enum variant you can
//! use](nested::ExampleEnum::Beta).
//!
//! [trait]: ExampleTrait::bar
pub struct ExampleStruct;
impl ExampleStruct {
pub fn foo(&self) {}
}
pub trait ExampleTrait {
fn bar();
}
pub mod nested {
pub enum ExampleEnum {
Alpha,
Beta,
}
}
Produces this documentation:
Specifically, this HTML is generated:
<p>Check out ExampleStruct, especially this method, but the trait method is also cool. There is also an enum variant you can use.</p>

As of Rust 1.48, Rustdoc now supports direct intra-doc links.
Pre Rust 1.48:
Rustdoc seems to generate mostly deterministic filenames for constituent elements of a crate. Therefore if you have an enum named Complex you can generally link to it using:
[Complex](enum.Complex.html)
Similarly a struct called Point would look like:
[Point](struct.Point.html)
This should carry over to most definitions (fn, trait, and so on).
For referencing elements of a crate at different nesting levels, you can use relative paths (where each module is its own folder):
[Point](../model/struct.Point.html)
or use absolute paths:
[Point](/crate_name/model/struct.Point.html)
More of these "conventions", including anchors for specific fields, etc., can be deduced if one builds docs (cargo doc --no-deps --open) and navigates to the field or item they want and takes note of the URL. Remember that only pub items are published to docs.

If one wants to link some specific part of a struct e.g., a method named foo in the same struct (using stable rust, not nightly)
[foo](#method.foo)
or if it is in another struct
[foo](struct.OtherStruct.html#method.foo)

In Rust 1.49 nightly it works (1.48 stable not released yet):
[super::structs::WebApiResponse]
[mycrate::structs::WebApiResponse]
etc.
Read here

Since the documentation is written in Markdown, just use the Markdown syntax for Hyperlinks; i.e.
[anchor text](URL)
Also, take a look at this: https://doc.rust-lang.org/book/documentation.html

Related

Conditional compilation based on proc_macro

Is it possible to somehow detect in a crate that it's used in proc_macro and include some items based on that?
Let's say I have a token_parser crate with a Token enum:
pub struct Group;
pub struct Ident;
pub struct Punct;
pub struct Literal;
pub enum Token {
Group(Group),
Ident(Ident),
Punct(Punct),
Literal(Literal)
}
It's intended to be a wrapper for a proc_macro::TokenTree, so I want to be able to use it inside a proc_macro crates. I don't want to manualy implement a converting logic in every crate, so I want something like this:
#[cfg(proc_macro)]
impl From<proc_macro::TokenTree> for Token {
fn from(token: proc_macro::TokenTree) -> Self
{
todo!()
}
}
while still having an option to use token_parser crate in normal crates.
P.S I'm aware of proc_macro2 crate. I will probably use it (or even syn) in the end, for now I'm just trying to understand how to do something like that myself properly.
There are primarily two ways I would reach for based on how I want to enable such functionality.
feature for project-based enabling
If you want it only available when opted for, that's a fantastic case to use a cargo feature. Crates that want to use such functionality can then choose to enable this feature while other crates can choose to not enable the feature. Whether this feature should be default typically depends on how the library author believes it should/is used most of the time.
cfg for platform-based enabling
As you may have seen from reading the proc_macro2 source, they conditionally enable a cfg in their build script1. On the wasm32 platform target it is disabled, otherwise it is enabled. This way is very useful in cases where enabling functionality mostly depends on the platform.

Make a one to one mapping from string to enum variant without using a match statement

I'm writing code to parse HTTP requests. I'd rather keep some things like request methods and response codes as enums because of their exhaustibility.
But it also means that for each of those enums I would have to make a From<String> implementation. The obvious way to do it is to match against a plethora of constant strings. That seems like a lot of almost identical code which I would want to factor out.
Someone suggested I use a macro to do it, but my knowledge of rust macros is limited so it made me question some things:
How can I ensure the argument is of type &str or String? Macros can take expressions, but I don't want to use type_name and panic if it doesn't match as it seems to be a very dirty fix.
How can I convert a string to a token stream? So far I've seen that the proc_macro crate offers that functionality, but is it possible to do with simple declarative macro?
Is it possible to achieve one to one mapping by any other means? I hoped I could pre-initialize enum variants with some known values like in Java.
You really want to use a library for this. You can write the macro yourself, but someone else has already made a battle-tested version of what you're trying to do.
Use strum's EnumString derive:
In Cargo.toml:
[dependencies]
strum = "0.24"
strum_macros = "0.24"
In your source code: (eg main.rs)
use std::str::FromStr;
use strum_macros::EnumString;
#[derive(Debug, EnumString)]
enum MyEnum {
Foo,
Bar,
Baz,
}
fn main() {
dbg!(MyEnum::from_str("Foo").unwrap());
}
Gives you
[src/main.rs:12] MyEnum::from_str("Foo").unwrap() = Foo
For more details see The documentation for the FromString derive and strum's readme.

How to use #[deprecated] for renaming public struct in backwards compatible way?

I see that I can use the #[deprecated] marker, but somehow it is not working in the following workflow:
I renamed all my MyOldStruct to MyNewStruct in my library.
Added a #deprecated note to pub use MyNewStruct as MyOldStruct.
pub struct MyNewStruct{};
#[deprecated]
pub use MyOldStruct as MyNewStruct;
Any ideas what might be going wrong here? I am viewing if it shows as deprecated in cargo docs.
Use a type alias:
#[deprecated]
pub type MyOldStruct = MyNewStruct;
See it emit a warning on the playground.
I will note that using a type alias for renaming and deprecating things doesn't work for everything: an aliased tuple struct can't use the new name construct a value as shown in the docs, and this method obviously doesn't work for traits since they aren't types and we don't have trait aliases yet.

How can I split up a large impl over multiple files?

I really don't like monolithic implementations of the functions for a class (in C++ speak). In that language I can split things up as I like; in Rust there are strict rules about what goes in what files.
I have about 2000 lines (no comments/ docs) of impl for a struct. Logically they can be broken up into different sets; functions for managing aspect A, functions for managing aspect B, ... They all noodle on the struct's data big time, so chopping the struct up further wont help.
I saw in one answer that you can have
// in thing.rs
struct Thing{
.......
}
impl Thing{
fn1
fn2
}
// in more_thing.rs
use crate::thing::*;
impl Thing{
fn3,
fn4
}
// in lib.rs
mod thing;
mod more_thing;
This works, almost (I was surprised it worked at all). Its a kind of half way house. The problem is that for the methods in more_thing.rs I have to declare the fields of Thing all pub. Which is doable but not great. Are there any other options?
I know I can limit the pub scope but still it blows encapsulation.
All non-pub items in a module are still visible in its submodules. Just make more_thing a submodule of thing instead of a sibling. You can do this by putting it in a directory named thing, and putting the mod declaration inside thing.rs:
// thing.rs (or thing/mod.rs; see below)
pub struct Thing {
field: i32,
}
// Note the lack of `pub`: `more` is only an implementation detail
mod more;
// thing/more.rs
use super::Thing;
impl Thing {
// Although it is defined in a non-`pub` module, this method will be visible anywhere
// `Thing` is because it is marked `pub` and is a member of `Thing`. You can use
// `pub(crate)` or `pub(super)` instead to get different levels of visibility, or
// leave it private and it will only be available in the current module (thing::more)
pub fn field(&self) -> i32 {
// because more is a submodule of thing, non-`pub` members are visible here.
self.field
}
}
If you wish to keep all the Thing-related files in the thing directory, you can rename thing.rs to the special filename thing/mod.rs and it will work in exactly the same way.
All methods are private by default in Rust, which means they are only accessible in the scope of their containing module (which is never larger than a file), in this case thing.rs. thing.rs is just as remote to more_thing.rs as any libraries and external code; it may as well be a separate crate. In essence, you are trying to declare a private method on an external item, which of course fails.
However, this can be a bit confusing because when it comes to orphan rules, you can always implement traits for any item in the same crate, not just the same module. This is because trait implementations are always public (as long as you can access both the trait and the item implementing it; the actual orphan rules are a bit more complicated but this is the basic idea).
In essence: trait implementations are public, but method implementations are private by default. In order to implement public things you need at least public access, and in order to implement private things you need private access.
Instead, one solution is to simply declare a function that takes your item as an argument. For example, in more_thing.rs:
use super::thing::Thing;
fn foo(thing: &Thing) {
// ...
}
Why not put impl blocks in the same file?
in thing.rs
struct Thing {
.......
}
impl Thing {
fn1
fn2
}
impl Thing {
fn3
fn4
}
The methods are splited though there is still a large file.

How to expose method to its sibling and parent only but not to client using that crate in rust [duplicate]

I have a crate that has lots of code, so I've split it into multiple files/modules. However, some modules have internal unsafe stuff (e.g. raw pointers) that I need to make public to the different modules, but I don't want to expose to users of my crate. How can I do that?
The only way I can think of is to actually have my crate just be one big module, but then there's no way to split it into different files, other than this solution which seems a bit hacky.
Normally when I come up against a real world problem that the simple examples in the Rust docs don't adequately explain I just copy a popular real world crate, e.g. git2-rs, but that just seems to effectively make everything public, including the raw pointers.
In order for an item to be exported from a library crate, there must be at least one path leading to it in which every component is public. This means that all you need to make an item public within your crate but not exported from the crate (I'll call this "internal" from now on, to mimic C# terminology) is to put it in a private module under the crate root.
However, that solution is quite restrictive. What if you'd like to have a module with exported functions and internal functions? In order to export some functions, we need to make the module public, and that mean all public items in that module will be exported as well.
Since Rust 1.18, there's a solution adapted to this kind of scenario: pub(restricted). This feature lets you specify "how public" an item should be. The syntax is pretty flexible (you can make an item visible to a particular module tree instead of the whole crate), but if you want to keep it simple, pub(crate) will make an item accessible anywhere within the crate, but not to other crates (equivalent to internal in C#).
For example, suppose we'd like to have a module util in which foo is exported (as mycrate::util::foo), bar is internal and baz is private to the module. The code might look like this:
pub mod util {
pub fn foo() {
unimplemented!()
}
pub(crate) fn bar() {
unimplemented!()
}
fn baz() {
unimplemented!()
}
}
If you're stuck on pre-1.18 Rust, there's a workaround, but it's a bit clunky. It involves defining all your items in private modules, and reexporting only those that you want to make public (with pub use) in public modules that only contain reexports. Here's what the example above would look like:
pub mod util {
pub use util_impl::foo;
}
mod util_impl {
pub fn foo() {
unimplemented!()
}
pub fn bar() {
unimplemented!()
}
fn baz() {
unimplemented!()
}
}
Not only is this not easy to read and understand, it doesn't cover all situations where pub can be used. For example, how would you make some fields of an exported struct accessible in other modules in the same crate without also exporting them? The only option would be to expose a wrapper with a single private field whose type is the struct that has public fields; that works fine if you want to hide all fields from other crates, but not if you want to expose some fields and make some other fields internal in the same struct.

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