prepared the search for the generics in the impl and struct definitions to determine if it makes sense to suggest adding the extra parameter to the generics of the struct on the impl ... for ...<> line

Author: TomtheCoder2

compiler/rustc_hir_analysis/src/impl_wf_check.rs

@@ -25,6 +25,7 @@ use rustc_span::{ErrorGuaranteed, kw};
 
 use crate::constrained_generic_params as cgp;
 use crate::errors::UnconstrainedGenericParameter;
+use crate::hir::def::Res;
 
 mod min_specialization;
 
@@ -253,8 +254,7 @@ pub(crate) fn enforce_impl_non_lifetime_params_are_constrained(
     res
 }
 
-/// A HIR visitor that checks if a specific generic parameter (by its `DefId`)
-/// is used within a given HIR tree.
+/// Use a Visitor to find usages of the type or lifetime parameter
 struct ParamUsageVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
     /// The `DefId` of the generic parameter we are looking for.
@@ -270,10 +270,8 @@ impl<'tcx> Visitor<'tcx> for ParamUsageVisitor<'tcx> {
         self.tcx
     }
 
-    /// We use `ControlFlow` to stop visiting as soon as we find what we're looking for.
     type Result = ControlFlow<()>;
 
-    /// This is the primary method for finding usages of type or const parameters.
     fn visit_path(&mut self, path: &Path<'tcx>, _id: HirId) -> Self::Result {
         if let Some(res_def_id) = path.res.opt_def_id() {
             if res_def_id == self.param_def_id {
@@ -318,12 +316,25 @@ fn suggest_to_remove_or_use_generic(
         return;
     };
 
-    // search if the parameter is used in the impl body
-    let mut visitor = ParamUsageVisitor {
-        tcx, // Pass the TyCtxt
-        param_def_id: param.def_id,
-        found: false,
+    // get the struct_def_id from the self type
+    let Some(struct_def_id) = (|| {
+        let ty = hir_impl.self_ty;
+        if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind
+            && let Res::Def(_, def_id) = path.res
+        {
+            Some(def_id)
+        } else {
+            None
+        }
+    })() else {
+        return;
     };
+    let generics = tcx.generics_of(struct_def_id);
+    // println!("number of struct generics: {}", generics.own_params.len());
+    // println!("number of impl generics: {}", hir_impl.generics.params.len());
+
+    // search if the parameter is used in the impl body
+    let mut visitor = ParamUsageVisitor { tcx, param_def_id: param.def_id, found: false };
 
     for item_ref in hir_impl.items {
         let _ = visitor.visit_impl_item_ref(item_ref);