https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125537
--- Comment #1 from Wang Jinghao <zheng.xianyuwang at gmail dot com> --- This is caused by temporarily enabling `processing_template_decl' in `tsubst_contract' when the return type is `auto', causing the type-conversion `IMPLICIT_CONV_EXPR' to be left until the genericization stage. Narrowing the conditions under which `processing_template_decl' is enabled fixes the issue.
