feat(sync): add typed presence projection

req: sync/001

req: sync/005

hemx-sync-macros/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "hemx-sync-macros"
+version.workspace = true
+edition.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1"
+quote = "1"
+syn = { version = "2", features = ["full"] }

hemx-sync-macros/src/lib.rs

@@ -0,0 +1,65 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, Error, FnArg, ItemFn, Pat, ReturnType};
+
+#[proc_macro_attribute]
+pub fn presence(attributes: TokenStream, item: TokenStream) -> TokenStream {
+    if !attributes.is_empty() {
+        return Error::new(
+            proc_macro2::Span::call_site(),
+            "#[hemx_sync::presence] does not accept arguments",
+        )
+        .to_compile_error()
+        .into();
+    }
+
+    let mut function = parse_macro_input!(item as ItemFn);
+    if function.sig.asyncness.is_some() {
+        return Error::new_spanned(
+            function.sig.asyncness,
+            "presence projections must be synchronous",
+        )
+        .to_compile_error()
+        .into();
+    }
+    if matches!(function.sig.output, ReturnType::Default) {
+        return Error::new_spanned(
+            &function.sig,
+            "presence projections must return impl IntoEffect",
+        )
+        .to_compile_error()
+        .into();
+    }
+    let argument = match function.sig.inputs.first() {
+        Some(FnArg::Typed(argument)) if function.sig.inputs.len() == 1 => argument,
+        _ => {
+            return Error::new_spanned(
+                &function.sig.inputs,
+                "presence projections require exactly one typed presence argument",
+            )
+            .to_compile_error()
+            .into();
+        }
+    };
+    let argument_name = match argument.pat.as_ref() {
+        Pat::Ident(argument) => argument.ident.clone(),
+        pattern => {
+            return Error::new_spanned(
+                pattern,
+                "presence projection argument must be a simple identifier",
+            )
+            .to_compile_error()
+            .into();
+        }
+    };
+
+    let body = function.block;
+    function.sig.output = syn::parse_quote!(-> impl ::hemx_sync::PresenceUpdate);
+    function.block = Box::new(syn::parse_quote!({
+        let __hemx_sync_channel =
+            ::hemx_sync::PresenceScope::presence_channel(&#argument_name);
+        let __hemx_sync_effect = (|| #body)();
+        ::hemx_sync::PresenceProjection::new(__hemx_sync_channel, __hemx_sync_effect)
+    }));
+    quote!(#function).into()
+}