Port example 04

lib/ruin_app_proc_macros/src/lib.rs

@@ -4,8 +4,8 @@ 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,
+    Error, Expr, FnArg, Ident, ItemFn, ItemStruct, Pat, PatIdent, Path, Result, ReturnType, Token,
+    Type, braced, parenthesized, parse_macro_input,
 };
 
 #[proc_macro_attribute]
@@ -29,6 +29,16 @@ pub fn view(input: TokenStream) -> TokenStream {
     expand_node(&root.root).into()
 }
 
+#[proc_macro_attribute]
+pub fn context_provider(attr: TokenStream, item: TokenStream) -> TokenStream {
+    let value_ty = parse_macro_input!(attr as Type);
+    let item_struct = parse_macro_input!(item as ItemStruct);
+    match expand_context_provider(item_struct, value_ty) {
+        Ok(tokens) => tokens.into(),
+        Err(error) => error.to_compile_error().into(),
+    }
+}
+
 fn expand_component(mut function: ItemFn) -> Result<proc_macro2::TokenStream> {
     validate_component_function(&function)?;
 
@@ -256,6 +266,34 @@ fn expand_component(mut function: ItemFn) -> Result<proc_macro2::TokenStream> {
     })
 }
 
+fn expand_context_provider(
+    item_struct: ItemStruct,
+    value_ty: Type,
+) -> Result<proc_macro2::TokenStream> {
+    if !item_struct.generics.params.is_empty() || item_struct.generics.where_clause.is_some() {
+        return Err(Error::new_spanned(
+            &item_struct.generics,
+            "context providers cannot be generic",
+        ));
+    }
+    if !matches!(item_struct.fields, syn::Fields::Unit) {
+        return Err(Error::new_spanned(
+            &item_struct.fields,
+            "context providers must be unit structs",
+        ));
+    }
+
+    let ident = &item_struct.ident;
+
+    Ok(quote! {
+        #item_struct
+
+        impl ::ruin_app::ContextKey for #ident {
+            type Value = #value_ty;
+        }
+    })
+}
+
 fn validate_component_function(function: &ItemFn) -> Result<()> {
     let signature = &function.sig;
 
@@ -443,6 +481,9 @@ fn looks_like_node(input: ParseStream<'_>) -> Result<bool> {
 
 fn expand_node(node: &Node) -> proc_macro2::TokenStream {
     let path = &node.path;
+    if is_provider_path(path) {
+        return expand_provider_node(node);
+    }
     let prop_calls = node.props.iter().map(|property| {
         let name = &property.name;
         let value = &property.value;
@@ -465,6 +506,34 @@ fn expand_node(node: &Node) -> proc_macro2::TokenStream {
     }
 }
 
+fn expand_provider_node(node: &Node) -> proc_macro2::TokenStream {
+    let path = &node.path;
+    let value = match node.props.as_slice() {
+        [Property { name, value }] if name == "value" => value,
+        _ => {
+            return Error::new_spanned(
+                path,
+                "provide::<Context>(...) expects exactly one `value = ...` property",
+            )
+            .to_compile_error();
+        }
+    };
+    let child = match node.children.as_slice() {
+        [child] => expand_child(child),
+        _ => {
+            return Error::new_spanned(path, "provide::<Context>(...) requires exactly one child")
+                .to_compile_error();
+        }
+    };
+
+    quote! {
+        ::ruin_app::#path(
+            #value,
+            || ::ruin_app::IntoView::into_view(#child),
+        )
+    }
+}
+
 fn expand_children(children: &[Child]) -> proc_macro2::TokenStream {
     match children {
         [] => quote! { () },
@@ -491,3 +560,12 @@ fn is_component_path(path: &Path) -> bool {
         .map(|ch| ch.is_ascii_uppercase())
         .unwrap_or(false)
 }
+
+fn is_provider_path(path: &Path) -> bool {
+    !is_component_path(path)
+        && path
+            .segments
+            .last()
+            .map(|segment| segment.ident == "provide")
+            .unwrap_or(false)
+}