Validate single-segment types in attribute macros

1 files changed, 29 insertions, 0 deletions

diff --git a/mingling_macros/src/lib.rs b/mingling_macros/src/lib.rs
index 213c397..175c7e5 100644
--- a/mingling_macros/src/lib.rs
+++ b/mingling_macros/src/lib.rs
@@ -68,6 +68,35 @@ pub(crate) static RENDERERS_EXIST: Lazy<Mutex<BTreeSet<String>>> =
 pub(crate) static HELP_REQUESTS: Lazy<Mutex<BTreeSet<String>>> =
     Lazy::new(|| Mutex::new(BTreeSet::new()));
 
+/// Checks that a TypePath is a simple single-segment identifier (no `::` in the path).
+///
+/// This is used by `#[renderer]`, `#[help]`, `#[chain]`, and `#[completion]` attribute macros
+/// to ensure that the type in the function signature is a bare identifier like `Empty`,
+/// not a qualified path like `other::Empty`.
+///
+/// Returns `None` if the type is valid, or a `compile_error!` token stream if it contains `::`.
+pub(crate) fn check_single_segment_type(
+    type_path: &syn::TypePath,
+    attr_name: &str,
+) -> Option<proc_macro2::TokenStream> {
+    if type_path.path.segments.len() > 1 {
+        let type_str = quote! { #type_path };
+        Some(quote! {
+            compile_error!(concat!(
+                "The type `",
+                #type_str,
+                "` in ",
+                #attr_name,
+                " function must be a simple single-segment type, ",
+                "e.g. `Empty` instead of `other::Empty`. ",
+                "Qualified paths with `::` are not allowed here."
+            ));
+        })
+    } else {
+        None
+    }
+}
+
 /// Creates a `Node` from a dot-separated path string.
 ///
 /// Each segment is converted to kebab-case (unless it starts with `_`).