Construct external Rust types with named fields

crates/rune-macros/src/any.rs

@@ -138,7 +138,7 @@ pub(crate) fn expand_install_with(
 
     match &input.data {
         syn::Data::Struct(st) => {
-            expand_struct_install_with(cx, installers, st, tokens, attr)?;
+            expand_struct_install_with(cx, installers, ident, st, tokens, attr)?;
         }
         syn::Data::Enum(en) => {
             expand_enum_install_with(cx, installers, ident, en, tokens, attr, generics)?;
@@ -164,6 +164,7 @@ pub(crate) fn expand_install_with(
 fn expand_struct_install_with(
     cx: &Context,
     installers: &mut Vec<TokenStream>,
+    ident: &syn::Ident,
     st: &syn::DataStruct,
     tokens: &Tokens,
     attr: &TypeAttr,
@@ -217,13 +218,32 @@ fn expand_struct_install_with(
 
     match &st.fields {
         syn::Fields::Named(fields) => {
+            let constructor = attr
+                .constructor
+                .then(|| {
+                    let args = fields.named.iter().map(|f| {
+                        let ident = f.ident.as_ref().expect("named fields must have an Ident");
+                        let typ = &f.ty;
+                        quote!(#ident: #typ)
+                    });
+
+                    let field_names = fields.named.iter().map(|f| f.ident.as_ref());
+
+                    quote!(|#(#args),*| {
+                        #ident {
+                            #(#field_names),*
+                        }
+                    })
+                })
+                .map(|c| quote!(.constructor(#c)?));
+
             let fields = fields.named.iter().flat_map(|f| {
                 let ident = f.ident.as_ref()?;
                 Some(syn::LitStr::new(&ident.to_string(), ident.span()))
             });
 
             installers.push(quote! {
-                module.type_meta::<Self>()?.make_named_struct(&[#(#fields,)*])?.static_docs(&#docs);
+                module.type_meta::<Self>()?.make_named_struct(&[#(#fields,)*])?#constructor.static_docs(&#docs);
             });
         }
         syn::Fields::Unnamed(fields) => {

crates/rune-macros/src/context.rs

@@ -72,6 +72,8 @@ pub(crate) struct TypeAttr {
     pub(crate) parse: ParseKind,
     /// `#[rune(item = <path>)]`.
     pub(crate) item: Option<syn::Path>,
+    /// `#[rune(constructor)]`.
+    pub(crate) constructor: bool,
     /// Parsed documentation.
     pub(crate) docs: Vec<syn::Expr>,
 }
@@ -441,6 +443,8 @@ impl Context {
                         // Parse `#[rune(install_with = <path>)]`
                         meta.input.parse::<Token![=]>()?;
                         attr.install_with = Some(parse_path_compat(meta.input)?);
+                    } else if meta.path == CONSTRUCTOR {
+                        attr.constructor = true;
                     } else {
                         return Err(syn::Error::new_spanned(
                             &meta.path,

crates/rune/src/compile/context.rs

@@ -429,17 +429,51 @@ impl Context {
 
         let kind = if let Some(spec) = &ty.spec {
             match spec {
-                TypeSpecification::Struct(fields) => meta::Kind::Struct {
-                    fields: match fields {
-                        Fields::Named(fields) => meta::Fields::Named(meta::FieldsNamed {
-                            fields: fields.iter().copied().map(Box::<str>::from).collect(),
-                        }),
-                        Fields::Unnamed(args) => meta::Fields::Unnamed(*args),
-                        Fields::Empty => meta::Fields::Empty,
-                    },
-                    constructor: None,
-                    parameters,
-                },
+                TypeSpecification::Struct(fields) => {
+                    let constructor = match &ty.constructor {
+                        Some(c) => {
+                            let hash = Hash::type_hash(&item);
+
+                            let signature = meta::Signature {
+                                #[cfg(feature = "doc")]
+                                is_async: false,
+                                #[cfg(feature = "doc")]
+                                args: Some(match fields {
+                                    Fields::Named(names) => names.len(),
+                                    Fields::Unnamed(args) => *args,
+                                    Fields::Empty => 0,
+                                }),
+                                #[cfg(feature = "doc")]
+                                return_type: Some(ty.hash),
+                                #[cfg(feature = "doc")]
+                                argument_types: Box::from([]),
+                            };
+
+                            self.insert_native_fn(hash, c)?;
+                            Some(signature)
+                        }
+                        None => None,
+                    };
+
+                    meta::Kind::Struct {
+                        fields: match fields {
+                            Fields::Named(fields) => meta::Fields::Named(meta::FieldsNamed {
+                                fields: fields
+                                    .iter()
+                                    .copied()
+                                    .enumerate()
+                                    .map(|(position, name)| {
+                                        (Box::<str>::from(name), meta::FieldMeta { position })
+                                    })
+                                    .collect(),
+                            }),
+                            Fields::Unnamed(args) => meta::Fields::Unnamed(*args),
+                            Fields::Empty => meta::Fields::Empty,
+                        },
+                        constructor,
+                        parameters,
+                    }
+                }
                 TypeSpecification::Enum(en) => {
                     for (index, variant) in en.variants.iter().enumerate() {
                         let Some(fields) = &variant.fields else {
@@ -495,7 +529,13 @@ impl Context {
                                             fields: names
                                                 .iter()
                                                 .copied()
-                                                .map(Box::<str>::from)
+                                                .enumerate()
+                                                .map(|(position, name)| {
+                                                    (
+                                                        Box::<str>::from(name),
+                                                        meta::FieldMeta { position },
+                                                    )
+                                                })
                                                 .collect(),
                                         })
                                     }
@@ -874,7 +914,14 @@ impl Context {
                     index,
                     fields: match fields {
                         Fields::Named(fields) => meta::Fields::Named(meta::FieldsNamed {
-                            fields: fields.iter().copied().map(Box::<str>::from).collect(),
+                            fields: fields
+                                .iter()
+                                .copied()
+                                .enumerate()
+                                .map(|(position, name)| {
+                                    (Box::<str>::from(name), meta::FieldMeta { position })
+                                })
+                                .collect(),
                         }),
                         Fields::Unnamed(args) => meta::Fields::Unnamed(*args),
                         Fields::Empty => meta::Fields::Empty,

crates/rune/src/compile/context_error.rs

@@ -77,6 +77,9 @@ pub enum ContextError {
     ConflictingVariant {
         item: ItemBuf,
     },
+    ConstructorConflict {
+        type_info: TypeInfo,
+    },
     ValueError {
         error: VmError,
     },
@@ -196,6 +199,12 @@ impl fmt::Display for ContextError {
             ContextError::ConflictingVariant { item } => {
                 write!(f, "Variant with `{item}` already exists")?;
             }
+            ContextError::ConstructorConflict { type_info } => {
+                write!(
+                    f,
+                    "Constructor for type `{type_info}` has already been registered"
+                )?;
+            }
             ContextError::ValueError { error } => {
                 write!(f, "Error when converting to constant value: {error}")?;
             }

crates/rune/src/compile/meta.rs

@@ -3,7 +3,7 @@
 use core::fmt;
 
 use crate::no_std::borrow::Cow;
-use crate::no_std::collections::HashSet;
+use crate::no_std::collections::HashMap;
 use crate::no_std::path::Path;
 use crate::no_std::prelude::*;
 
@@ -287,7 +287,14 @@ pub struct Import {
 #[non_exhaustive]
 pub struct FieldsNamed {
     /// Fields associated with the type.
-    pub(crate) fields: HashSet<Box<str>>,
+    pub(crate) fields: HashMap<Box<str>, FieldMeta>,
+}
+
+/// Metadata for a single named field.
+#[derive(Debug, Clone)]
+pub struct FieldMeta {
+    /// Position of the field in its containing type declaration.
+    pub(crate) position: usize,
 }
 
 /// Item and the module that the item belongs to.

crates/rune/src/compile/v1/assemble.rs

@@ -1957,7 +1957,9 @@ fn expr_object<'hir>(
 ) -> compile::Result<Asm<'hir>> {
     let guard = cx.scopes.child(span)?;
 
-    for assign in hir.assignments {
+    let base = cx.scopes.total(span)?;
+
+    for assign in hir.assignments.iter() {
         expr(cx, &assign.assign, Needs::Value)?.apply(cx)?;
         cx.scopes.alloc(&span)?;
     }
@@ -1976,6 +1978,10 @@ fn expr_object<'hir>(
         hir::ExprObjectKind::StructVariant { hash } => {
             cx.asm.push(Inst::StructVariant { hash, slot }, span);
         }
+        hir::ExprObjectKind::ExternalType { hash, args } => {
+            reorder_field_assignments(cx, hir, base, span)?;
+            cx.asm.push(Inst::Call { hash, args }, span);
+        }
         hir::ExprObjectKind::Anonymous => {
             cx.asm.push(Inst::Object { slot }, span);
         }
@@ -1991,6 +1997,56 @@ fn expr_object<'hir>(
     Ok(Asm::top(span))
 }
 
+/// Reorder the position of the field assignments on the stack so that they
+/// match the expected argument order when invoking the constructor function.
+fn reorder_field_assignments<'hir>(
+    cx: &mut Ctxt<'_, 'hir, '_>,
+    hir: &hir::ExprObject<'hir>,
+    base: usize,
+    span: &dyn Spanned,
+) -> compile::Result<()> {
+    let mut order = Vec::with_capacity(hir.assignments.len());
+
+    for assign in hir.assignments {
+        let Some(position) = assign.position else {
+            return Err(compile::Error::msg(
+                span,
+                format_args!("Missing position for field assignment {}", assign.key.1),
+            ));
+        };
+
+        order.push(position);
+    }
+
+    for a in 0..hir.assignments.len() {
+        loop {
+            let Some(&b) = order.get(a) else {
+                return Err(compile::Error::msg(
+                    span,
+                    "Order out-of-bounds",
+                ));
+            };
+
+            if a == b {
+                break;
+            }
+
+            order.swap(a, b);
+
+            let (Some(a), Some(b)) = (base.checked_add(a), base.checked_add(b)) else {
+                return Err(compile::Error::msg(
+                    span,
+                    "Field repositioning out-of-bounds",
+                ));
+            };
+
+            cx.asm.push(Inst::Swap { a, b }, span);
+        }
+    }
+
+    Ok(())
+}
+
 /// Assemble a range expression.
 #[instrument(span = span)]
 fn expr_range<'hir>(

crates/rune/src/hir/hir.rs

@@ -580,6 +580,7 @@ pub(crate) enum ExprObjectKind {
     UnitStruct { hash: Hash },
     Struct { hash: Hash },
     StructVariant { hash: Hash },
+    ExternalType { hash: Hash, args: usize },
     Anonymous,
 }
 
@@ -601,6 +602,8 @@ pub(crate) struct FieldAssign<'hir> {
     pub(crate) key: (Span, &'hir str),
     /// The assigned expression of the field.
     pub(crate) assign: Expr<'hir>,
+    /// The position of the field in its containing type declaration.
+    pub(crate) position: Option<usize>,
 }
 
 /// A literal vector.

crates/rune/src/hir/lowering.rs

@@ -330,7 +330,7 @@ pub(crate) fn expr_object<'hir>(
     let span = ast;
     let mut keys_dup = HashMap::new();
 
-    let assignments = &*iter!(&ast.assignments, |(ast, _)| {
+    let assignments = &mut *iter!(&ast.assignments, |(ast, _)| {
         let key = object_key(cx, &ast.key)?;
 
         if let Some(existing) = keys_dup.insert(key.1, key.0) {
@@ -362,25 +362,31 @@ pub(crate) fn expr_object<'hir>(
         hir::FieldAssign {
             key: (key.0.span(), key.1),
             assign,
+            position: None,
         }
     });
 
-    let check_object_fields = |fields: &HashSet<_>, item: &Item| {
+    let mut check_object_fields = |fields: &HashMap<_, meta::FieldMeta>, item: &Item| {
         let mut fields = fields.clone();
 
-        for assign in assignments {
-            if !fields.remove(assign.key.1) {
-                return Err(compile::Error::new(
-                    assign.key.0,
-                    ErrorKind::LitObjectNotField {
-                        field: assign.key.1.into(),
-                        item: item.to_owned(),
-                    },
-                ));
-            }
+        for assign in assignments.iter_mut() {
+            match fields.remove(assign.key.1) {
+                Some(field_meta) => {
+                    assign.position = Some(field_meta.position);
+                }
+                None => {
+                    return Err(compile::Error::new(
+                        assign.key.0,
+                        ErrorKind::LitObjectNotField {
+                            field: assign.key.1.into(),
+                            item: item.to_owned(),
+                        },
+                    ));
+                }
+            };
         }
 
-        if let Some(field) = fields.into_iter().next() {
+        if let Some(field) = fields.into_keys().next() {
             return Err(compile::Error::new(
                 span,
                 ErrorKind::LitObjectMissingField {
@@ -405,15 +411,23 @@ pub(crate) fn expr_object<'hir>(
                     fields: meta::Fields::Empty,
                     ..
                 } => {
-                    check_object_fields(&HashSet::new(), item)?;
+                    check_object_fields(&HashMap::new(), item)?;
                     hir::ExprObjectKind::UnitStruct { hash: meta.hash }
                 }
                 meta::Kind::Struct {
                     fields: meta::Fields::Named(st),
+                    constructor,
                     ..
                 } => {
                     check_object_fields(&st.fields, item)?;
-                    hir::ExprObjectKind::Struct { hash: meta.hash }
+
+                    match constructor {
+                        Some(_) => hir::ExprObjectKind::ExternalType {
+                            hash: meta.hash,
+                            args: st.fields.len(),
+                        },
+                        None => hir::ExprObjectKind::Struct { hash: meta.hash },
+                    }
                 }
                 meta::Kind::Variant {
                     fields: meta::Fields::Named(st),
@@ -1167,7 +1181,7 @@ fn pat<'hir>(cx: &mut Ctxt<'hir, '_, '_>, ast: &ast::Pat) -> compile::Result<hir
                         ));
                     };
 
-                    let mut fields = st.fields.clone();
+                    let mut fields: HashSet<_> = st.fields.keys().cloned().collect();
 
                     for binding in bindings.iter() {
                         if !fields.remove(binding.key()) {