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

<!--
if this PR closes one or more issues, you can automatically link the PR
with
them by using one of the [*linking
keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword),
e.g.
- this PR should close #xxxx
- fixes #xxxx

you can also mention related issues, PRs or discussions!
-->

# Description
<!--
Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.

Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.
-->
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
<!--
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->
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
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->

crates/nu-derive-value/src/attributes.rs

@@ -6,12 +6,14 @@ use crate::{error::DeriveError, HELPER_ATTRIBUTE};
 #[derive(Debug)]
 pub struct ContainerAttributes {
     pub rename_all: Case,
+    pub type_name: Option<String>,
 }
 
 impl Default for ContainerAttributes {
     fn default() -> Self {
         Self {
             rename_all: Case::Snake,
+            type_name: None,
         }
     }
 }
@@ -59,6 +61,11 @@ impl ContainerAttributes {
                         };
                         container_attrs.rename_all = case;
                     }
+                    "type_name" => {
+                        let type_name: LitStr = meta.value()?.parse()?;
+                        let type_name = type_name.value();
+                        container_attrs.type_name = Some(type_name);
+                    }
                     ident => {
                         err = Err(DeriveError::UnexpectedAttribute {
                             meta_span: ident.span(),

crates/nu-derive-value/src/from.rs

@@ -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
+/// This function provides the impl signature for `FromValue`.
-/// structs.
-/// Other than this, 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 {
+/// Struct with passed type name:
-        Fields::Named(fields) => {
+/// ```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`.
+/// implementation is a lot simpler.
-/// The actual implementation for `FromValue::from_value` is handled by [`enum_from_value`].
+/// 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
-/// Since variants are difficult to type with the current type system, this function uses the
+/// implementation, but if `#[nu_value(type_name = "...")]` if given, we use that.
-/// default implementation for `expected_type`.
 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.

crates/nu-derive-value/src/into.rs

@@ -50,8 +50,6 @@ pub fn derive_into_value(input: TokenStream2) -> Result<TokenStream2, DeriveErro
 /// For structs with unnamed fields, this generates a `Value::List` with each field in the list.
 /// For unit structs, this generates `Value::Nothing`, because there is no data.
 ///
-/// Note: The helper attribute `#[nu_value(...)]` is currently not allowed on structs.
-///
 /// # Examples
 ///
 /// These examples show what the macro would generate.
@@ -109,7 +107,7 @@ fn struct_into_value(
     generics: Generics,
     attrs: Vec<Attribute>,
 ) -> Result<TokenStream2, DeriveError> {
-    attributes::deny(&attrs)?;
+    let _ = ContainerAttributes::parse_attrs(attrs.iter())?;
     attributes::deny_fields(&data.fields)?;
     let record = match &data.fields {
         Fields::Named(fields) => {

crates/nu-derive-value/src/tests.rs

@@ -85,28 +85,6 @@ fn unexpected_attribute() {
     );
 }
 
-#[test]
-fn deny_attribute_on_structs() {
-    let input = quote! {
-        #[nu_value]
-        struct SomeStruct;
-    };
-
-    let from_res = derive_from_value(input.clone());
-    assert!(
-        matches!(from_res, Err(DeriveError::InvalidAttributePosition { .. })),
-        "expected `DeriveError::InvalidAttributePosition`, got {:?}",
-        from_res
-    );
-
-    let into_res = derive_into_value(input);
-    assert!(
-        matches!(into_res, Err(DeriveError::InvalidAttributePosition { .. })),
-        "expected `DeriveError::InvalidAttributePosition`, got {:?}",
-        into_res
-    );
-}
-
 #[test]
 fn deny_attribute_on_fields() {
     let input = quote! {

crates/nu-protocol/src/value/from_value.rs

@@ -34,10 +34,14 @@ use std::{
 /// [`#[serde(rename_all = "...")]`](https://serde.rs/container-attrs.html#rename_all) are valid
 /// here.
 ///
+/// Additionally, you can use `#[nu_value(type_name = "...")]` in the derive macro to set a custom type name
+/// for `FromValue::expected_type`. This will result in a `Type::Custom` with the specified type name.
+/// This can be useful in situations where the default type name is not desired.
+///
 /// ```
 /// # use nu_protocol::{FromValue, Value, ShellError};
 /// #[derive(FromValue, Debug, PartialEq)]
-/// #[nu_value(rename_all = "COBOL-CASE")]
+/// #[nu_value(rename_all = "COBOL-CASE", type_name = "birb")]
 /// enum Bird {
 ///     MountainEagle,
 ///     ForestOwl,
@@ -48,6 +52,11 @@ use std::{
 ///     Bird::from_value(Value::test_string("RIVER-DUCK")).unwrap(),
 ///     Bird::RiverDuck
 /// );
+///
+/// assert_eq!(
+///     &Bird::expected_type().to_string(),
+///     "birb"
+/// );
 /// ```
 pub trait FromValue: Sized {
     // TODO: instead of ShellError, maybe we could have a FromValueError that implements Into<ShellError>

crates/nu-protocol/src/value/test_derive.rs

@@ -494,3 +494,24 @@ fn bytes_roundtrip() {
         .into_test_value();
     assert_eq!(expected, actual);
 }
+
+#[test]
+fn struct_type_name_attr() {
+    #[derive(FromValue, Debug)]
+    #[nu_value(type_name = "struct")]
+    struct TypeNameStruct;
+
+    assert_eq!(
+        TypeNameStruct::expected_type().to_string().as_str(),
+        "struct"
+    );
+}
+
+#[test]
+fn enum_type_name_attr() {
+    #[derive(FromValue, Debug)]
+    #[nu_value(type_name = "enum")]
+    struct TypeNameEnum;
+
+    assert_eq!(TypeNameEnum::expected_type().to_string().as_str(), "enum");
+}