better errors for type arguments of collections

1 files changed, 20 insertions, 3 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 67c1223..1a84a09 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -53,9 +53,11 @@ mod syn_utils;
 mod transform;
 
 macro_rules! abort {
-    ($span:expr, $message:literal) => {
-        quote_spanned! {$span => compile_error!($message);}.into()
-    };
+    ($span:expr, $message:literal $(,$args:tt)*) => {{
+        let msg = format!($message $(,$args)*);
+        let tokens = quote_spanned! {$span => compile_error!(#msg);}.into();
+        tokens
+    }};
 }
 
 #[proc_macro_attribute]
@@ -119,6 +121,21 @@ pub fn dynamize(_attr: TokenStream, input: TokenStream) -> TokenStream {
                     MethodError::Transform(TransformError::UnsupportedType) => {
                         return abort!(span, "dynamize does not know how to convert this type")
                     }
+                    MethodError::Transform(TransformError::ExpectedAtLeastNTypes(n)) => {
+                        return abort!(
+                            span,
+                            "dynamize expects at least {} generic type arguments for this type",
+                            n
+                        )
+                    }
+                    MethodError::Transform(TransformError::AssocTypeAfterFirstNTypes(n, ident)) => {
+                        return abort!(
+                            span,
+                            "for {} dynamize supports associated types only within the first {} generic type parameters",
+                            ident,
+                            n
+                        )
+                    }
                     MethodError::UnconvertedAssocType => {
                         return abort!(span, "dynamize does not support associated types here")
                     }