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Change expected type for derived FromValue implementations via attribute (#13647)

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# Description
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In this PR I expanded the helper attribute `#[nu_value]` on
`#[derive(FromValue)]`. It now allows the usage of `#[nu_value(type_name
= "...")]` to set a type name for the `FromValue::expected_type`
implementation. Currently it only uses the default implementation but
I'd like to change that without having to manually implement the entire
trait on my own.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
Users that derive `FromValue` may now change the name of the expected
type.

# Tests + Formatting
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I added some tests that check if this feature work and updated the
documentation about the derive macro.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting
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This commit is contained in:
Piepmatz
2024-08-23 13:47:15 +02:00
committed by GitHub
parent 712fec166d
commit 39b0f3bdda
6 changed files with 117 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

96
crates/nu-derive-value/src/from.rs
View File

@ -42,9 +42,7 @@ pub fn derive_from_value(input: TokenStream2) -> Result<TokenStream2, DeriveErro
/// Implements the `#[derive(FromValue)]` macro for structs.
///
/// This function ensures that the helper attribute is not used anywhere, as it is not supported for
/// structs.
/// Other than this, this function provides the impl signature for `FromValue`.
/// This function provides the impl signature for `FromValue`.
/// The implementation for `FromValue::from_value` is handled by [`struct_from_value`] and the
/// `FromValue::expected_type` is handled by [`struct_expected_type`].
fn derive_struct_from_value(
@ -53,11 +51,12 @@ fn derive_struct_from_value(
generics: Generics,
attrs: Vec<Attribute>,
) -> Result<TokenStream2, DeriveError> {
attributes::deny(&attrs)?;
let container_attrs = ContainerAttributes::parse_attrs(attrs.iter())?;
attributes::deny_fields(&data.fields)?;
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let from_value_impl = struct_from_value(&data);
let expected_type_impl = struct_expected_type(&data.fields);
let expected_type_impl =
struct_expected_type(&data.fields, container_attrs.type_name.as_deref());
Ok(quote! {
#[automatically_derived]
impl #impl_generics nu_protocol::FromValue for #ident #ty_generics #where_clause {
@ -219,13 +218,16 @@ fn struct_from_value(data: &DataStruct) -> TokenStream2 {
/// `list[type0, type1, type2]`.
/// No fields expect the `Type::Nothing`.
///
/// If `#[nu_value(type_name = "...")]` is used, the output type will be `Type::Custom` with that
/// passed name.
///
/// # Examples
///
/// These examples show what the macro would generate.
///
/// Struct with named fields:
/// ```rust
/// #[derive(IntoValue)]
/// #[derive(FromValue)]
/// struct Pet {
/// name: String,
/// age: u8,
@ -256,7 +258,7 @@ fn struct_from_value(data: &DataStruct) -> TokenStream2 {
///
/// Struct with unnamed fields:
/// ```rust
/// #[derive(IntoValue)]
/// #[derive(FromValue)]
/// struct Color(u8, u8, u8);
///
/// impl nu_protocol::FromValue for Color {
@ -276,7 +278,7 @@ fn struct_from_value(data: &DataStruct) -> TokenStream2 {
///
/// Unit struct:
/// ```rust
/// #[derive(IntoValue)]
/// #[derive(FromValue)]
/// struct Unicorn;
///
/// impl nu_protocol::FromValue for Color {
@ -285,9 +287,30 @@ fn struct_from_value(data: &DataStruct) -> TokenStream2 {
/// }
/// }
/// ```
fn struct_expected_type(fields: &Fields) -> TokenStream2 {
let ty = match fields {
Fields::Named(fields) => {
///
/// Struct with passed type name:
/// ```rust
/// #[derive(FromValue)]
/// #[nu_value(type_name = "bird")]
/// struct Parrot;
///
/// impl nu_protocol::FromValue for Parrot {
/// fn expected_type() -> nu_protocol::Type {
/// nu_protocol::Type::Custom(
/// <std::string::String as std::convert::From::<&str>>::from("bird")
/// .into_boxed_str()
/// )
/// }
/// }
/// ```
fn struct_expected_type(fields: &Fields, attr_type_name: Option<&str>) -> TokenStream2 {
let ty = match (fields, attr_type_name) {
(_, Some(type_name)) => {
quote!(nu_protocol::Type::Custom(
<std::string::String as std::convert::From::<&str>>::from(#type_name).into_boxed_str()
))
}
(Fields::Named(fields), _) => {
let fields = fields.named.iter().map(|field| {
let ident = field.ident.as_ref().expect("named has idents");
let ident_s = ident.to_string();
@ -301,7 +324,7 @@ fn struct_expected_type(fields: &Fields) -> TokenStream2 {
std::vec![#(#fields),*].into_boxed_slice()
))
}
Fields::Unnamed(fields) => {
(Fields::Unnamed(fields), _) => {
let mut iter = fields.unnamed.iter();
let fields = fields.unnamed.iter().map(|field| {
let ty = &field.ty;
@ -324,7 +347,7 @@ fn struct_expected_type(fields: &Fields) -> TokenStream2 {
)
}
}
Fields::Unit => quote!(nu_protocol::Type::Nothing),
(Fields::Unit, _) => quote!(nu_protocol::Type::Nothing),
};
quote! {
@ -338,23 +361,25 @@ fn struct_expected_type(fields: &Fields) -> TokenStream2 {
///
/// This function constructs the implementation of the `FromValue` trait for enums.
/// It is designed to be on the same level as [`derive_struct_from_value`], even though this
/// function only provides the impl signature for `FromValue`.
/// The actual implementation for `FromValue::from_value` is handled by [`enum_from_value`].
///
/// Since variants are difficult to type with the current type system, this function uses the
/// default implementation for `expected_type`.
/// implementation is a lot simpler.
/// The main `FromValue::from_value` implementation is handled by [`enum_from_value`].
/// The `FromValue::expected_type` implementation is usually kept empty to use the default
/// implementation, but if `#[nu_value(type_name = "...")]` if given, we use that.
fn derive_enum_from_value(
ident: Ident,
data: DataEnum,
generics: Generics,
attrs: Vec<Attribute>,
) -> Result<TokenStream2, DeriveError> {
let container_attrs = ContainerAttributes::parse_attrs(attrs.iter())?;
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let from_value_impl = enum_from_value(&data, &attrs)?;
let expected_type_impl = enum_expected_type(container_attrs.type_name.as_deref());
Ok(quote! {
#[automatically_derived]
impl #impl_generics nu_protocol::FromValue for #ident #ty_generics #where_clause {
#from_value_impl
#expected_type_impl
}
})
}
@ -448,6 +473,41 @@ fn enum_from_value(data: &DataEnum, attrs: &[Attribute]) -> Result<TokenStream2,
})
}
/// Implements `FromValue::expected_type` for enums.
///
/// Since it's difficult to name the type of an enum in the current type system, we want to use the
/// default implementation if `#[nu_value(type_name = "...")]` was *not* given.
/// For that, a `None` value is returned, for a passed type name we return something like this:
/// ```rust
/// #[derive(IntoValue)]
/// #[nu_value(type_name = "sunny | cloudy | raining")]
/// enum Weather {
/// Sunny,
/// Cloudy,
/// Raining
/// }
///
/// impl nu_protocol::FromValue for Weather {
/// fn expected_type() -> nu_protocol::Type {
/// nu_protocol::Type::Custom(
/// <std::string::String as std::convert::From::<&str>>::from("sunny | cloudy | raining")
/// .into_boxed_str()
/// )
/// }
/// }
/// ```
fn enum_expected_type(attr_type_name: Option<&str>) -> Option<TokenStream2> {
let type_name = attr_type_name?;
Some(quote! {
fn expected_type() -> nu_protocol::Type {
nu_protocol::Type::Custom(
<std::string::String as std::convert::From::<&str>>::from(#type_name)
.into_boxed_str()
)
}
})
}
/// Parses a `Value` into self.
///
/// This function handles the actual parsing of a `Value` into self.