From 136859154b88758e33a5cbe57d7bd70f1d31615f Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 8 Jan 2025 11:34:40 -0800
Subject: [PATCH 1/2] Add regression test for issue 405

    error[E0599]: the method `as_display` exists for reference `&<T as FromStr>::Err`, but its trait bounds were not satisfied
       --> tests/test_generics.rs:178:13
        |
    178 |     #[error("couldn't parse entry: {0}")]
        |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ method cannot be called on `&<T as FromStr>::Err` due to unsatisfied trait bounds
        |
        = note: the following trait bounds were not satisfied:
                `<T as FromStr>::Err: std::fmt::Display`
                which is required by `&<T as FromStr>::Err: AsDisplay<'_>`
---
 tests/test_generics.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tests/test_generics.rs b/tests/test_generics.rs
index 36f1181..bcbfee0 100644
--- a/tests/test_generics.rs
+++ b/tests/test_generics.rs
@@ -1,6 +1,7 @@
 #![allow(clippy::needless_late_init, clippy::uninlined_format_args)]
 
 use core::fmt::{self, Debug, Display};
+use core::str::FromStr;
 use thiserror::Error;
 
 pub struct NoFormat;
@@ -160,6 +161,24 @@ pub struct StructFromGeneric<E> {
 #[error(transparent)]
 pub struct StructTransparentGeneric<E>(pub E);
 
+// Should expand to:
+//
+//     impl<T: FromStr> Display for AssociatedTypeError<T>
+//     where
+//         T::Err: Display;
+//
+//     impl<T: FromStr> Error for AssociatedTypeError<T>
+//     where
+//         Self: Debug + Display;
+//
+#[derive(Error, Debug)]
+pub enum AssociatedTypeError<T: FromStr> {
+    #[error("couldn't parse matrix")]
+    Other,
+    #[error("couldn't parse entry: {0}")]
+    EntryParseError(T::Err),
+}
+
 // Regression test for https://github.com/dtolnay/thiserror/issues/345
 #[test]
 fn test_no_bound_on_named_fmt() {

From 6b3e1e50b27d9f90fd4a4be098d4693e50609784 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 8 Jan 2025 11:41:16 -0800
Subject: [PATCH 2/2] Generate trait bounds on associated types

---
 impl/src/generics.rs | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/impl/src/generics.rs b/impl/src/generics.rs
index 254c2ed..26fe0a9 100644
--- a/impl/src/generics.rs
+++ b/impl/src/generics.rs
@@ -25,11 +25,12 @@ impl<'a> ParamsInScope<'a> {
 
 fn crawl(in_scope: &ParamsInScope, ty: &Type, found: &mut bool) {
     if let Type::Path(ty) = ty {
-        if ty.qself.is_none() {
-            if let Some(ident) = ty.path.get_ident() {
-                if in_scope.names.contains(ident) {
-                    *found = true;
-                }
+        if let Some(qself) = &ty.qself {
+            crawl(in_scope, &qself.ty, found);
+        } else {
+            let front = ty.path.segments.first().unwrap();
+            if front.arguments.is_none() && in_scope.names.contains(&front.ident) {
+                *found = true;
             }
         }
         for segment in &ty.path.segments {