Proc macros for components, views

lib/ruin_app_proc_macros/src/lib.rs

@@ -0,0 +1,490 @@
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::{format_ident, quote};
+use syn::parse::{Parse, ParseStream};
+use syn::punctuated::Punctuated;
+use syn::{
+    Error, Expr, FnArg, Ident, ItemFn, Pat, PatIdent, Path, Result, ReturnType, Token, Type,
+    braced, parenthesized, parse_macro_input,
+};
+
+#[proc_macro_attribute]
+pub fn component(attr: TokenStream, item: TokenStream) -> TokenStream {
+    if !proc_macro2::TokenStream::from(attr).is_empty() {
+        return Error::new(Span::call_site(), "#[component] takes no arguments")
+            .to_compile_error()
+            .into();
+    }
+
+    let function = parse_macro_input!(item as ItemFn);
+    match expand_component(function) {
+        Ok(tokens) => tokens.into(),
+        Err(error) => error.to_compile_error().into(),
+    }
+}
+
+#[proc_macro]
+pub fn view(input: TokenStream) -> TokenStream {
+    let root = parse_macro_input!(input as ViewRoot);
+    expand_node(&root.root).into()
+}
+
+fn expand_component(mut function: ItemFn) -> Result<proc_macro2::TokenStream> {
+    validate_component_function(&function)?;
+
+    let vis = function.vis.clone();
+    let component_name = function.sig.ident.clone();
+    let render_name = format_ident!("__ruin_app_render_{}", component_name);
+    function.sig.ident = render_name.clone();
+    function
+        .attrs
+        .push(syn::parse_quote!(#[allow(non_snake_case)]));
+
+    let props = function
+        .sig
+        .inputs
+        .iter()
+        .map(parse_prop)
+        .collect::<Result<Vec<_>>>()?;
+
+    let builder_name = format_ident!("__{}Builder", component_name);
+
+    let builder_tokens = if props.is_empty() {
+        quote! {
+            #vis struct #builder_name;
+
+            impl #builder_name {
+                #vis fn children(self, _children: ()) -> #component_name {
+                    #component_name
+                }
+            }
+        }
+    } else {
+        let missing_names = props
+            .iter()
+            .map(|prop| format_ident!("__{}__{}_Missing", component_name, prop.ident))
+            .collect::<Vec<_>>();
+        let present_names = props
+            .iter()
+            .map(|prop| format_ident!("__{}__{}_Present", component_name, prop.ident))
+            .collect::<Vec<_>>();
+        let state_idents = (0..props.len())
+            .map(|index| format_ident!("P{index}"))
+            .collect::<Vec<_>>();
+        let field_idents = props.iter().map(|prop| &prop.ident).collect::<Vec<_>>();
+        let marker_structs = props
+            .iter()
+            .zip(missing_names.iter())
+            .zip(present_names.iter())
+            .map(|((prop, missing), present)| {
+                let ty = &prop.ty;
+                quote! {
+                    #[allow(non_camel_case_types)]
+                    #vis struct #missing;
+                    #[allow(non_camel_case_types)]
+                    #vis struct #present(#ty);
+                }
+            });
+
+        let builder_methods = props.iter().enumerate().map(|(index, prop)| {
+            let value_ident = &prop.ident;
+            let value_ty = &prop.ty;
+            let missing_at_index = &missing_names[index];
+            let present_at_index = &present_names[index];
+
+            let impl_generics = state_idents
+                .iter()
+                .enumerate()
+                .filter(|(current, _)| *current != index)
+                .map(|(_, ident)| ident);
+            let impl_generics = impl_generics.collect::<Vec<_>>();
+
+            let self_builder_args = state_idents
+                .iter()
+                .enumerate()
+                .map(|(current, ident)| {
+                    if current == index {
+                        quote! { #missing_at_index }
+                    } else {
+                        quote! { #ident }
+                    }
+                })
+                .collect::<Vec<_>>();
+
+            let next_builder_args = state_idents
+                .iter()
+                .enumerate()
+                .map(|(current, ident)| {
+                    if current == index {
+                        quote! { #present_at_index }
+                    } else {
+                        quote! { #ident }
+                    }
+                })
+                .collect::<Vec<_>>();
+
+            let field_initializers = field_idents
+                .iter()
+                .enumerate()
+                .map(|(current, field_ident)| {
+                    if current == index {
+                        quote! { #field_ident: #present_at_index(#value_ident) }
+                    } else {
+                        quote! { #field_ident: self.#field_ident }
+                    }
+                })
+                .collect::<Vec<_>>();
+
+            if impl_generics.is_empty() {
+                quote! {
+                    impl #builder_name<#(#self_builder_args),*> {
+                        #vis fn #value_ident(self, #value_ident: #value_ty) -> #builder_name<#(#next_builder_args),*> {
+                            #builder_name {
+                                #(#field_initializers),*
+                            }
+                        }
+                    }
+                }
+            } else {
+                quote! {
+                    impl<#(#impl_generics),*> #builder_name<#(#self_builder_args),*> {
+                        #vis fn #value_ident(self, #value_ident: #value_ty) -> #builder_name<#(#next_builder_args),*> {
+                            #builder_name {
+                                #(#field_initializers),*
+                            }
+                        }
+                    }
+                }
+            }
+        });
+
+        let ready_builder_args = present_names
+            .iter()
+            .map(|present| quote! { #present })
+            .collect::<Vec<_>>();
+        let missing_builder_args = missing_names
+            .iter()
+            .map(|missing| quote! { #missing })
+            .collect::<Vec<_>>();
+        let field_extractors = field_idents
+            .iter()
+            .map(|field_ident| quote! { #field_ident: builder.#field_ident.0 });
+
+        quote! {
+            #(#marker_structs)*
+
+            #vis struct #builder_name<#(#state_idents),*> {
+                #(#field_idents: #state_idents),*
+            }
+
+            #(#builder_methods)*
+
+            impl #builder_name<#(#ready_builder_args),*> {
+                #vis fn children(self, _children: ()) -> #component_name {
+                    #component_name::from_builder(self)
+                }
+            }
+
+            impl #component_name {
+                fn from_builder(builder: #builder_name<#(#ready_builder_args),*>) -> Self {
+                    Self {
+                        #(#field_extractors),*
+                    }
+                }
+            }
+
+            impl ::ruin_app::Component for #component_name {
+                type Builder = #builder_name<#(#missing_builder_args),*>;
+
+                fn builder() -> Self::Builder {
+                    #builder_name {
+                        #(#field_idents: #missing_names),*
+                    }
+                }
+
+                fn render(&self) -> ::ruin_app::View {
+                    ::ruin_app::IntoView::into_view(#render_name(
+                        #(::core::clone::Clone::clone(&self.#field_idents)),*
+                    ))
+                }
+            }
+        }
+    };
+
+    let render_call = if props.is_empty() {
+        quote! { #render_name() }
+    } else {
+        let field_idents = props.iter().map(|prop| &prop.ident);
+        quote! { #render_name(#(::core::clone::Clone::clone(&self.#field_idents)),*) }
+    };
+
+    let component_tokens = if props.is_empty() {
+        quote! {
+            #vis struct #component_name;
+
+            #builder_tokens
+
+            impl ::ruin_app::Component for #component_name {
+                type Builder = #builder_name;
+
+                fn builder() -> Self::Builder {
+                    #builder_name
+                }
+
+                fn render(&self) -> ::ruin_app::View {
+                    ::ruin_app::IntoView::into_view(#render_call)
+                }
+            }
+        }
+    } else {
+        let field_idents = props.iter().map(|prop| &prop.ident);
+        let field_types = props.iter().map(|prop| &prop.ty);
+        quote! {
+            #vis struct #component_name {
+                #( #field_idents: #field_types ),*
+            }
+
+            #builder_tokens
+        }
+    };
+
+    Ok(quote! {
+        #function
+
+        #component_tokens
+    })
+}
+
+fn validate_component_function(function: &ItemFn) -> Result<()> {
+    let signature = &function.sig;
+
+    if signature.asyncness.is_some() {
+        return Err(Error::new_spanned(
+            signature.asyncness,
+            "components must be synchronous functions",
+        ));
+    }
+    if !signature.generics.params.is_empty() || signature.generics.where_clause.is_some() {
+        return Err(Error::new_spanned(
+            &signature.generics,
+            "generic components are not supported yet",
+        ));
+    }
+    if signature.constness.is_some() {
+        return Err(Error::new_spanned(
+            signature.fn_token,
+            "components cannot be const",
+        ));
+    }
+    if signature.unsafety.is_some() {
+        return Err(Error::new_spanned(
+            signature.fn_token,
+            "components cannot be unsafe",
+        ));
+    }
+    if signature.abi.is_some() {
+        return Err(Error::new_spanned(
+            &signature.abi,
+            "components cannot declare an ABI",
+        ));
+    }
+    if signature.variadic.is_some() {
+        return Err(Error::new_spanned(
+            &signature.variadic,
+            "components cannot be variadic",
+        ));
+    }
+    for input in &signature.inputs {
+        let FnArg::Typed(typed) = input else {
+            return Err(Error::new_spanned(
+                input,
+                "methods with `self` are not supported by #[component]",
+            ));
+        };
+        let Pat::Ident(PatIdent { ident, .. }) = typed.pat.as_ref() else {
+            return Err(Error::new_spanned(
+                &typed.pat,
+                "component props must be simple identifier bindings",
+            ));
+        };
+        if ident == "children" {
+            return Err(Error::new_spanned(
+                ident,
+                "`children` is reserved for the generated builder finalizer",
+            ));
+        }
+    }
+
+    match &signature.output {
+        ReturnType::Default => Err(Error::new_spanned(
+            &signature.ident,
+            "components must return a view-like value",
+        )),
+        ReturnType::Type(_, _) => Ok(()),
+    }
+}
+
+struct Prop {
+    ident: Ident,
+    ty: Type,
+}
+
+fn parse_prop(input: &FnArg) -> Result<Prop> {
+    let FnArg::Typed(typed) = input else {
+        return Err(Error::new_spanned(
+            input,
+            "methods with `self` are not supported by #[component]",
+        ));
+    };
+    let Pat::Ident(PatIdent { ident, .. }) = typed.pat.as_ref() else {
+        return Err(Error::new_spanned(
+            &typed.pat,
+            "component props must be simple identifier bindings",
+        ));
+    };
+
+    Ok(Prop {
+        ident: ident.clone(),
+        ty: (*typed.ty).clone(),
+    })
+}
+
+struct ViewRoot {
+    root: Node,
+}
+
+impl Parse for ViewRoot {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let root = input.parse::<Node>()?;
+        if !input.is_empty() {
+            return Err(input.error("view! expects a single root node"));
+        }
+        Ok(Self { root })
+    }
+}
+
+struct Node {
+    path: Path,
+    props: Vec<Property>,
+    children: Vec<Child>,
+}
+
+struct Property {
+    name: Ident,
+    value: Expr,
+}
+
+enum Child {
+    Node(Node),
+    Expr(Expr),
+}
+
+impl Parse for Node {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let path = input.parse::<Path>()?;
+
+        let props_content;
+        parenthesized!(props_content in input);
+        let props = Punctuated::<Property, Token![,]>::parse_terminated(&props_content)?
+            .into_iter()
+            .collect::<Vec<_>>();
+
+        let children_content;
+        braced!(children_content in input);
+        let mut children = Vec::new();
+        while !children_content.is_empty() {
+            if looks_like_node(&children_content)? {
+                children.push(Child::Node(children_content.parse()?));
+            } else {
+                let expr = children_content.parse::<Expr>()?;
+                if children_content.peek(Token![;]) {
+                    let _ = children_content.parse::<Token![;]>()?;
+                }
+                children.push(Child::Expr(expr));
+            }
+        }
+
+        Ok(Self {
+            path,
+            props,
+            children,
+        })
+    }
+}
+
+impl Parse for Property {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        Ok(Self {
+            name: input.parse()?,
+            value: {
+                let _ = input.parse::<Token![=]>()?;
+                input.parse()?
+            },
+        })
+    }
+}
+
+fn looks_like_node(input: ParseStream<'_>) -> Result<bool> {
+    let fork = input.fork();
+    if fork.parse::<Path>().is_err() {
+        return Ok(false);
+    }
+    if !fork.peek(syn::token::Paren) {
+        return Ok(false);
+    }
+    let props_content;
+    parenthesized!(props_content in fork);
+    let _ = Punctuated::<Property, Token![,]>::parse_terminated(&props_content)?;
+    Ok(fork.peek(syn::token::Brace))
+}
+
+fn expand_node(node: &Node) -> proc_macro2::TokenStream {
+    let path = &node.path;
+    let prop_calls = node.props.iter().map(|property| {
+        let name = &property.name;
+        let value = &property.value;
+        quote! { .#name(#value) }
+    });
+    let children = expand_children(&node.children);
+
+    if is_component_path(path) {
+        quote! {
+            #path::builder()
+                #(#prop_calls)*
+                .children(#children)
+        }
+    } else {
+        quote! {
+            ::ruin_app::#path()
+                #(#prop_calls)*
+                .children(#children)
+        }
+    }
+}
+
+fn expand_children(children: &[Child]) -> proc_macro2::TokenStream {
+    match children {
+        [] => quote! { () },
+        [child] => expand_child(child),
+        many => {
+            let items = many.iter().map(expand_child);
+            quote! { ( #(#items),* ) }
+        }
+    }
+}
+
+fn expand_child(child: &Child) -> proc_macro2::TokenStream {
+    match child {
+        Child::Node(node) => expand_node(node),
+        Child::Expr(expr) => quote! { #expr },
+    }
+}
+
+fn is_component_path(path: &Path) -> bool {
+    path.segments
+        .last()
+        .map(|segment| segment.ident.to_string())
+        .and_then(|name| name.chars().next())
+        .map(|ch| ch.is_ascii_uppercase())
+        .unwrap_or(false)
+}