add an error message if you attempt to pass indirect args via guaranteed tail calls.

Author: xacrimon

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1045,6 +1045,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // to generate `lifetime_end` when the call returns.
         let mut lifetime_ends_after_call: Vec<(Bx::Value, Size)> = Vec::new();
         'make_args: for (i, arg) in first_args.iter().enumerate() {
+            if tail && matches!(fn_abi.args[i].mode, PassMode::Indirect { .. }) {
+                bug!(
+                    r"Arguments using PassMode::Indirect are currently not supported for tail calls.
+                    See https://github.com/rust-lang/rust/pull/144232#discussion_r2218543841 for more information."
+                );
+            }
+
             let mut op = self.codegen_operand(bx, &arg.node);
 
             if let (0, Some(ty::InstanceKind::Virtual(_, idx))) = (i, instance.map(|i| i.def)) {