fix a ICE #102768

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -493,8 +493,10 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                         },
                         def_id.to_def_id(),
                     );
-                    if let Some(assoc_item) = assoc_item {
+                    if let Some(param)
-                        tcx.type_of(tcx.generics_of(assoc_item.def_id).params[idx].def_id)
+                        = assoc_item.map(|item| &tcx.generics_of(item.def_id).params[idx]).filter(|param| param.kind.is_ty_or_const())
+                    {
+                        tcx.type_of(param.def_id)
                     } else {
                         // FIXME(associated_const_equality): add a useful error message here.
                         tcx.ty_error_with_message(

src/test/ui/const-generics/generic_const_exprs/issue-102768.rs

@@ -0,0 +1,14 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+trait X {
+    type Y<'a>;
+}
+
+const _: () = {
+    fn f2<'a>(arg: Box<dyn X<Y<1> = &'a ()>>) {}
+    //~^ ERROR this associated type takes 1 lifetime argument but 0 lifetime arguments
+    //~| ERROR this associated type takes 0 generic arguments but 1 generic argument
+};
+
+fn main() {}

src/test/ui/const-generics/generic_const_exprs/issue-102768.stderr

@@ -0,0 +1,33 @@
+error[E0107]: this associated type takes 1 lifetime argument but 0 lifetime arguments were supplied
+  --> $DIR/issue-102768.rs:9:30
+   |
+LL |     fn f2<'a>(arg: Box<dyn X<Y<1> = &'a ()>>) {}
+   |                              ^ expected 1 lifetime argument
+   |
+note: associated type defined here, with 1 lifetime parameter: `'a`
+  --> $DIR/issue-102768.rs:5:10
+   |
+LL |     type Y<'a>;
+   |          ^ --
+help: add missing lifetime argument
+   |
+LL |     fn f2<'a>(arg: Box<dyn X<Y<'a, 1> = &'a ()>>) {}
+   |                                +++
+
+error[E0107]: this associated type takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/issue-102768.rs:9:30
+   |
+LL |     fn f2<'a>(arg: Box<dyn X<Y<1> = &'a ()>>) {}
+   |                              ^--- help: remove these generics
+   |                              |
+   |                              expected 0 generic arguments
+   |
+note: associated type defined here, with 0 generic parameters
+  --> $DIR/issue-102768.rs:5:10
+   |
+LL |     type Y<'a>;
+   |          ^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0107`.