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doc: transfer doc for BorshSerialize
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dj8yf0μl committed Dec 28, 2024
1 parent 0dc09cd commit 4561d4f
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264 changes: 1 addition & 263 deletions borsh-derive/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,269 +29,7 @@ fn check_attrs_get_cratename(input: &TokenStream) -> Result<Path, Error> {
cratename::get(&derive_input.attrs)
}

/**
# derive proc-macro for `borsh::ser::BorshSerialize` trait
## Bounds
Generally, `BorshSerialize` adds `borsh::ser::BorshSerialize` bound to any type parameter
found in item's fields.
```ignore
/// impl<U, V> borsh::ser::BorshSerialize for A<U, V>
/// where
/// U: borsh::ser::BorshSerialize,
/// V: borsh::ser::BorshSerialize,
#[derive(BorshSerialize)]
struct A<U, V> {
x: U,
y: V,
}
```
```ignore
/// impl<U, V> borsh::ser::BorshSerialize for A<U, V>
/// where
/// U: borsh::ser::BorshSerialize,
#[derive(BorshSerialize)]
struct A<U, V> {
x: U,
#[borsh(skip)]
y: V,
}
```
## Attributes
### 1. `#[borsh(crate = "path::to::borsh")]` (item level attribute)
###### syntax
Attribute takes literal string value, which is the syn's [Path] to `borsh` crate used.
###### usage
Attribute is optional.
1. If the attribute is not provided, [crate_name](proc_macro_crate::crate_name) is used to find a version of `borsh`
in `[dependencies]` of the relevant `Cargo.toml`. If there is no match, a compilation error, similar to the following, is raised:
```bash
1 error: proc-macro derive panicked
--> path/to/file.rs:27:10
|
27 | #[derive(BorshSerialize, BorshDeserialize)]
| ^^^^^^^^^^^^^^
|
= help: message: called `Result::unwrap()` on an `Err` value: CrateNotFound { crate_name: "borsh", path: "/path/to/Cargo.toml" }
```
2. If the attribute is provided, the check for `borsh` in `[dependencies]` of the relevant `Cargo.toml` is skipped.
Examples of usage:
```ignore
use reexporter::borsh::BorshSerialize;
// specifying the attribute removes need for a direct import of `borsh` into `[dependencies]`
#[derive(BorshSerialize)]
#[borsh(crate = "reexporter::borsh")]
struct B {
x: u64,
y: i32,
c: String,
}
```
```ignore
use reexporter::borsh::{self, BorshSerialize};
// specifying the attribute removes need for a direct import of `borsh` into `[dependencies]`
#[derive(BorshSerialize)]
#[borsh(crate = "borsh")]
struct B {
x: u64,
y: i32,
c: String,
}
```
### 2. `borsh(use_discriminant=<bool>)` (item level attribute)
This attribute is only applicable to enums.
`use_discriminant` allows to override the default behavior of serialization of enums with explicit discriminant.
`use_discriminant` is `false` behaves like version of borsh of 0.10.3.
You must specify `use_discriminant` for all enums with explicit discriminants in your project.
This is equivalent of borsh version 0.10.3 (explicit discriminant is ignored and this enum is equivalent to `A` without explicit discriminant):
```ignore
#[derive(BorshSerialize)]
#[borsh(use_discriminant = false)]
enum A {
A
B = 10,
}
```
To have explicit discriminant value serialized as is, you must specify `borsh(use_discriminant=true)` for enum.
```ignore
#[derive(BorshSerialize)]
#[borsh(use_discriminant = true)]
enum B {
A
B = 10,
}
```
###### borsh, expressions, evaluating to `isize`, as discriminant
This case is not supported:
```ignore
const fn discrim() -> isize {
0x14
}
#[derive(BorshSerialize)]
#[borsh(use_discriminant = true)]
enum X {
A,
B = discrim(), // expressions, evaluating to `isize`, which are allowed outside of `borsh` context
C,
D,
E = 10,
F,
}
```
###### borsh explicit discriminant does not support literal values outside of u8 range
This is not supported:
```ignore
#[derive(BorshSerialize)]
#[borsh(use_discriminant = true)]
enum X {
A,
B = 0x100, // literal values outside of `u8` range
C,
D,
E = 10,
F,
}
```
### 3. `#[borsh(skip)]` (field level attribute)
`#[borsh(skip)]` makes derive skip serializing annotated field.
`#[borsh(skip)]` makes derive skip adding any type parameters, present in the field, to parameters bound by `borsh::ser::BorshSerialize`.
```ignore
#[derive(BorshSerialize)]
struct A {
x: u64,
#[borsh(skip)]
y: f32,
}
```
### 4. `#[borsh(bound(serialize = ...))]` (field level attribute)
###### syntax
Attribute takes literal string value, which is a comma-separated list of syn's [WherePredicate](syn::WherePredicate)-s, which may be empty.
###### usage
Attribute adds possibility to override bounds for `BorshSerialize` in order to enable:
1. removal of bounds on type parameters from struct/enum definition itself and moving them to the trait's implementation block.
2. fixing complex cases, when derive hasn't figured out the right bounds on type parameters automatically.
```ignore
/// additional bound `T: Ord` (required by `HashMap`) is injected into
/// derived trait implementation via attribute to avoid adding the bounds on the struct itself
#[derive(BorshSerialize)]
struct A<T, U> {
a: String,
#[borsh(bound(serialize =
"T: borsh::ser::BorshSerialize + Ord,
U: borsh::ser::BorshSerialize"))]
b: HashMap<T, U>,
}
```
```ignore
/// derive here figures the bound erroneously as `T: borsh::ser::BorshSerialize`
#[derive(BorshSerialize)]
struct A<T, V>
where
T: TraitName,
{
#[borsh(bound(serialize = "<T as TraitName>::Associated: borsh::ser::BorshSerialize"))]
field: <T as TraitName>::Associated,
another: V,
}
```
###### interaction with `#[borsh(skip)]`
`#[borsh(bound(serialize = ...))]` replaces bounds, which are derived automatically,
irrelevant of whether `#[borsh(skip)]` attribute is present.
### 5. `#[borsh(serialize_with = ...)]` (field level attribute)
###### syntax
Attribute takes literal string value, which is a syn's [ExprPath](syn::ExprPath).
###### usage
Attribute adds possibility to specify full path of function, optionally qualified with generics,
with which to serialize the annotated field.
It may be used when `BorshSerialize` cannot be implemented for field's type, if it's from foreign crate.
It may be used to override the implementation of serialization for some other reason.
```ignore
use indexmap::IndexMap;
mod index_map_impl {
use super::IndexMap;
use core::hash::Hash;
pub fn serialize_index_map<
K: borsh::ser::BorshSerialize,
V: borsh::ser::BorshSerialize,
W: borsh::io::Write,
>(
obj: &IndexMap<K, V>,
writer: &mut W,
) -> ::core::result::Result<(), borsh::io::Error> {
let key_value_tuples = obj.iter().collect::<Vec<_>>();
borsh::BorshSerialize::serialize(&key_value_tuples, writer)?;
Ok(())
}
}
#[derive(BorshSerialize)]
struct B<K, V> {
#[borsh(
serialize_with = "index_map_impl::serialize_index_map",
)]
x: IndexMap<K, V>,
y: String,
}
```
###### usage (comprehensive example)
[borsh/examples/serde_json_value.rs](https://github.com/near/borsh-rs/blob/master/borsh/examples/serde_json_value.rs) is
a more complex example of how the attribute may be used.
###### interaction with `#[borsh(skip)]`
`#[borsh(serialize_with = ...)]` is not allowed to be used simultaneously with `#[borsh(skip)]`.
*/
/// moved to documnetation of **Derive Macro** `BorshSerialize` in `borsh` crate
#[proc_macro_derive(BorshSerialize, attributes(borsh))]
pub fn borsh_serialize(input: TokenStream) -> TokenStream {
let cratename = match check_attrs_get_cratename(&input) {
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6 changes: 5 additions & 1 deletion borsh/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -79,7 +79,11 @@ pub use borsh_derive::BorshSchema;

/// Derive macro available if borsh is built with `features = ["derive"]`.
#[cfg(feature = "derive")]
pub use borsh_derive::{BorshDeserialize, BorshSerialize};
pub use borsh_derive::BorshDeserialize;

#[doc = include_str!("../../docs/rustdoc_include/borsh_serialize.md")]
#[cfg(feature = "derive")]
pub use borsh_derive::BorshSerialize;

pub mod de;

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