https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119401
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:1949beb7dbe66687542f4a19d316914dd73fe84d commit r15-9066-g1949beb7dbe66687542f4a19d316914dd73fe84d Author: Jason Merrill <ja...@redhat.com> Date: Sat Mar 29 14:00:55 2025 -0400 c++: lambda in function template signature [PR119401] Here we instantiate the lambda three times in producing A<0>::f: 1) in tsubst_function_type, substituting the type of A<>::f 2) in tsubst_function_decl, substituting the parameters of A<>::f 3) in regenerate_decl_from_template when instantiating A<>::f The first one gets thrown away by maybe_rebuild_function_decl_type. Before r15-7202, we happily built all of them and mangled the result wrongly as lambda #3. After r15-7202, we try to mangle #3 as #1, which breaks because #1 is already mangled as #1. This patch avoids building #3 by suppressing regenerate_decl_from_template if the template signature includes a lambda, fixing the ICE. We now mangle the lambda as #2, which is still wrong. Addressing that should involve not calling tsubst_function_type from tsubst_function_decl, and building the type from the parms types in the first place rather than fixing it up in maybe_rebuild_function_decl_type. PR c++/119401 gcc/cp/ChangeLog: * pt.cc (regenerate_decl_from_template): Don't regenerate if the signature involves a lambda. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/lambda-targ11.C: New test.
