add a test case for generic_const_exprs in trait items

Author: TaKO8Ki

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -79,7 +79,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
                     let generics = tcx.generics_of(parent_def_id.to_def_id());
                     let param_def_idx = generics.param_def_id_to_index[&param_id.to_def_id()];
                     // In the above example this would be .params[..N#0]
-                    let params = generics.param_to(param_def_idx as usize, tcx).to_owned();
+                    let params = generics.params_to(param_def_idx as usize, tcx).to_owned();
                     let param_def_id_to_index =
                         params.iter().map(|param| (param.def_id, param.index)).collect();
 

compiler/rustc_middle/src/ty/generics.rs

@@ -220,12 +220,12 @@ impl<'tcx> Generics {
         }
     }
 
-    pub fn param_to(&'tcx self, param_index: usize, tcx: TyCtxt<'tcx>) -> &'tcx [GenericParamDef] {
+    pub fn params_to(&'tcx self, param_index: usize, tcx: TyCtxt<'tcx>) -> &'tcx [GenericParamDef] {
         if let Some(index) = param_index.checked_sub(self.parent_count) {
             &self.params[..index]
         } else {
             tcx.generics_of(self.parent.expect("parent_count > 0 but no parent?"))
-                .param_to(param_index, tcx)
+                .params_to(param_index, tcx)
         }
     }
 

src/test/ui/const-generics/generic_const_exprs/issue-105257.rs

@@ -3,6 +3,7 @@
 
 trait Trait<T> {
     fn fnc<const N: usize = "">(&self) {} //~ERROR defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
+    fn foo<const N: usize = { std::mem::size_of::<T>() }>(&self) {} //~ERROR defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
 }
 
 fn main() {}

src/test/ui/const-generics/generic_const_exprs/issue-105257.stderr

@@ -4,5 +4,11 @@ error: defaults for const parameters are only allowed in `struct`, `enum`, `type
 LL |     fn fnc<const N: usize = "">(&self) {}
    |            ^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
+  --> $DIR/issue-105257.rs:6:12
+   |
+LL |     fn foo<const N: usize = { std::mem::size_of::<T>() }>(&self) {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors