From f598bb75d47c45b69b3fe2952d53fcccf870e8b3 Mon Sep 17 00:00:00 2001
From: Michael Krasnitski <michael.krasnitski@gmail.com>
Date: Mon, 11 Sep 2023 21:43:27 -0400
Subject: [PATCH] Walk the left side of where bounds if the bounded type is not
 a generic parameter

---
 clippy_lints/src/extra_unused_type_parameters.rs |  7 ++++++-
 tests/ui/extra_unused_type_parameters.fixed      | 15 +++++++++++++++
 tests/ui/extra_unused_type_parameters.rs         | 15 +++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/clippy_lints/src/extra_unused_type_parameters.rs b/clippy_lints/src/extra_unused_type_parameters.rs
index c18006a71c26..0a885984abbf 100644
--- a/clippy_lints/src/extra_unused_type_parameters.rs
+++ b/clippy_lints/src/extra_unused_type_parameters.rs
@@ -246,8 +246,13 @@ impl<'cx, 'tcx> Visitor<'tcx> for TypeWalker<'cx, 'tcx> {
                 {
                     self.ty_params.remove(&def_id);
                 }
+            } else {
+                // If the bounded type isn't a generic param, but is instead a concrete generic
+                // type, any params we find nested inside of it are being used as concrete types,
+                // and can therefore can be considered used. So, we're fine to walk the left-hand
+                // side of the where bound.
+                walk_ty(self, predicate.bounded_ty);
             }
-            // Only walk the right-hand side of where bounds
             for bound in predicate.bounds {
                 walk_param_bound(self, bound);
             }
diff --git a/tests/ui/extra_unused_type_parameters.fixed b/tests/ui/extra_unused_type_parameters.fixed
index a4943344a11e..c9bebabdf17a 100644
--- a/tests/ui/extra_unused_type_parameters.fixed
+++ b/tests/ui/extra_unused_type_parameters.fixed
@@ -113,4 +113,19 @@ with_span!(
     }
 );
 
+mod issue11302 {
+    use std::fmt::Debug;
+    use std::marker::PhantomData;
+
+    #[derive(Debug)]
+    struct Wrapper<T>(PhantomData<T>);
+
+    fn store<T: 'static>(v: &mut Vec<Box<dyn Debug>>)
+    where
+        Wrapper<T>: Debug,
+    {
+        v.push(Box::new(Wrapper(PhantomData)));
+    }
+}
+
 fn main() {}
diff --git a/tests/ui/extra_unused_type_parameters.rs b/tests/ui/extra_unused_type_parameters.rs
index 6d85b1ce9d4f..1bc0047adf01 100644
--- a/tests/ui/extra_unused_type_parameters.rs
+++ b/tests/ui/extra_unused_type_parameters.rs
@@ -113,4 +113,19 @@ with_span!(
     }
 );
 
+mod issue11302 {
+    use std::fmt::Debug;
+    use std::marker::PhantomData;
+
+    #[derive(Debug)]
+    struct Wrapper<T>(PhantomData<T>);
+
+    fn store<T: 'static>(v: &mut Vec<Box<dyn Debug>>)
+    where
+        Wrapper<T>: Debug,
+    {
+        v.push(Box::new(Wrapper(PhantomData)));
+    }
+}
+
 fn main() {}