better error message for <Self as Foo>::X

1 files changed, 14 insertions, 1 deletions

diff --git a/src/transform.rs b/src/transform.rs
index 8de4c96..594d383 100644
--- a/src/transform.rs
+++ b/src/transform.rs
@@ -3,7 +3,7 @@ use std::collections::HashMap;
 use proc_macro2::Span;
 use quote::quote;
 use syn::{
-    spanned::Spanned, GenericArgument, Generics, Ident, PathArguments, TraitBound, Type,
+    spanned::Spanned, GenericArgument, Generics, Ident, PathArguments, QSelf, TraitBound, Type,
     TypeParamBound, TypePath, TypeReference, TypeTraitObject, WherePredicate,
 };
 
@@ -11,6 +11,7 @@ use crate::{
     filter_map_assoc_paths, match_assoc_type,
     parse_assoc_type::{BoxType, DestType},
     parse_trait_sig::{MethodError, TypeTransform},
+    path_is_assoc_type,
     syn_utils::{iter_path, iter_type, type_arguments_mut},
 };
 
@@ -26,6 +27,7 @@ pub enum TransformError {
     UnsupportedType,
     ExpectedAtLeastNTypes(usize),
     AssocTypeAfterFirstNTypes(usize, Ident),
+    QualifiedSelfAssociatedType,
 }
 
 impl TypeConverter<'_> {
@@ -57,6 +59,17 @@ impl TypeConverter<'_> {
     }
 
     pub fn convert_type(&self, type_: &mut Type) -> Result<TypeTransform, (Span, TransformError)> {
+        if let Type::Path(TypePath {
+            qself: Some(QSelf { ty, .. }),
+            ..
+        }) = type_
+        {
+            if let Type::Path(TypePath { qself: None, path }) = ty.as_ref() {
+                if path_is_assoc_type(path) {
+                    return Err((path.span(), TransformError::QualifiedSelfAssociatedType));
+                }
+            }
+        }
         if !iter_type(type_).any(match_assoc_type) {
             return Ok(TypeTransform::NoOp);
         }