https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120224
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-15 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:121235441d072c2f5fd4d2cc0c342d45d6ac481f commit r15-10173-g121235441d072c2f5fd4d2cc0c342d45d6ac481f Author: Patrick Palka <ppa...@redhat.com> Date: Thu Jun 5 11:07:25 2025 -0400 c++: substituting fn parm redeclared with dep alias tmpl [PR120224] Here we declare f twice, the second time around using a dependent alias template. Due to alias template transparency these are logically the same overload. But now the function type of f (produced from the first declaration) diverges from the type of its formal parameter (produced from the subsequent redefinition) in that substituting T=int succeeds for the function type but not for the formal parameter type. This eventually causes us to produce an undiagnosed error_mark_node in the AST of the function call, leading to failure of the sanity check check added in r14-6343-g0c018a74eb1aff. Before r14-6343 we would still go on to reject the testcase later at instantiation time, from regenerate_decl_from_template, making this a regression. To fix this, it seems we just need to propagate error_mark_node upon substitution failure into the type of a PARM_DECL. PR c++/120224 gcc/cp/ChangeLog: * pt.cc (tsubst_function_decl): Return error_mark_node if substituting into the formal parameter list failed. (tsubst_decl) <case PARM_DECL>: Return error_mark_node upon TREE_TYPE substitution failure, when in a SFINAE context. Return error_mark_node upon DECL_CHAIN substitution failure. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/alias-decl-80.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com> (cherry picked from commit 51e93aadc94940e2da854cf1321a7ab1aebf8d1a)
