Delay a span bug if we see ty/const generic params during writeback

Author: compiler-errors

compiler/rustc_typeck/src/check/writeback.rs

@@ -293,6 +293,17 @@ impl<'cx, 'tcx> Visitor<'tcx> for WritebackCx<'cx, 'tcx> {
         intravisit::walk_expr(self, e);
     }
 
+    fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
+        match &p.kind {
+            hir::GenericParamKind::Lifetime { .. } => {
+                // Nothing to write back here
+            }
+            hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => {
+                self.tcx().sess.delay_span_bug(p.span, format!("unexpected generic param: {p:?}"));
+            }
+        }
+    }
+
     fn visit_block(&mut self, b: &'tcx hir::Block<'tcx>) {
         self.visit_node_id(b.span, b.hir_id);
         intravisit::walk_block(self, b);

src/test/ui/closures/binder/disallow-const.rs

@@ -0,0 +1,6 @@
+#![feature(closure_lifetime_binder)]
+
+fn main() {
+    for<const N: i32> || -> () {};
+    //~^ ERROR only lifetime parameters can be used in this context
+}

src/test/ui/closures/binder/disallow-const.stderr

@@ -0,0 +1,8 @@
+error: only lifetime parameters can be used in this context
+  --> $DIR/disallow-const.rs:4:15
+   |
+LL |     for<const N: i32> || -> () {};
+   |               ^
+
+error: aborting due to previous error
+

src/test/ui/closures/binder/disallow-ty.rs

@@ -0,0 +1,6 @@
+#![feature(closure_lifetime_binder)]
+
+fn main() {
+    for<T> || -> () {};
+    //~^ ERROR only lifetime parameters can be used in this context
+}

src/test/ui/closures/binder/disallow-ty.stderr

@@ -0,0 +1,8 @@
+error: only lifetime parameters can be used in this context
+  --> $DIR/disallow-ty.rs:4:9
+   |
+LL |     for<T> || -> () {};
+   |         ^
+
+error: aborting due to previous error
+