Don't use raw parameter types in find_builder_fn

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -34,8 +34,8 @@ use rustc_middle::ty::IsSuggestable;
 use rustc_middle::ty::{self, GenericArgKind, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::def_id::DefIdSet;
 use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::Symbol;
 use rustc_span::{edit_distance, ExpnKind, FileName, MacroKind, Span};
+use rustc_span::{Symbol, DUMMY_SP};
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::error_reporting::on_unimplemented::OnUnimplementedNote;
 use rustc_trait_selection::traits::error_reporting::on_unimplemented::TypeErrCtxtExt as _;
@@ -1597,7 +1597,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .filter(|item| matches!(item.kind, ty::AssocKind::Fn) && !item.fn_has_self_parameter)
             .filter_map(|item| {
                 // Only assoc fns that return `Self`, `Option<Self>` or `Result<Self, _>`.
-                let ret_ty = self.tcx.fn_sig(item.def_id).skip_binder().output();
+                let ret_ty = self
+                    .tcx
+                    .fn_sig(item.def_id)
+                    .instantiate(self.tcx, self.fresh_args_for_item(DUMMY_SP, item.def_id))
+                    .output();
                 let ret_ty = self.tcx.instantiate_bound_regions_with_erased(ret_ty);
                 let ty::Adt(def, args) = ret_ty.kind() else {
                     return None;

tests/ui/issues/issue-30123.stderr

@@ -4,6 +4,11 @@ error[E0599]: no function or associated item named `new_undirected` found for st
 LL |     let ug = Graph::<i32, i32>::new_undirected();
    |                                 ^^^^^^^^^^^^^^ function or associated item not found in `Graph<i32, i32>`
    |
+note: if you're trying to build a new `issue_30123_aux::Graph<i32, i32>`, consider using `issue_30123_aux::Graph::<N, E>::new` which returns `issue_30123_aux::Graph<_, _>`
+  --> $DIR/auxiliary/issue-30123-aux.rs:14:5
+   |
+LL |     pub fn new() -> Self {
+   |     ^^^^^^^^^^^^^^^^^^^^
    = note: the function or associated item was found for
            - `issue_30123_aux::Graph<N, E, Undirected>`