Walk the left side of where bounds if the bounded type is not a generic parameter

Author: mkrasnitski

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);
             }

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() {}

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() {}