https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109651
--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:7bfb1550ccea7c426d50244e980f01f30db8ba0c commit r14-559-g7bfb1550ccea7c426d50244e980f01f30db8ba0c Author: Patrick Palka <ppa...@redhat.com> Date: Sun May 7 11:54:21 2023 -0400 c++: bound ttp in lambda function type [PR109651] After r14-11-g2245459c85a3f4 we now coerce the template arguments of a bound ttp again after level-lowering it. Notably a level-lowered ttp doesn't have DECL_CONTEXT set, so during this coercion we fall back to using current_template_parms to obtain the relevant set of in-scope parameters. But it turns out current_template_parms isn't properly set when substituting the function type of a generic lambda, and so if the type contains bound ttps that need to be lowered we'll crash during their attempted coercion. Specifically in the first testcase below, current_template_parms during the lambda type substitution (with T=int) is "1 U" instead of the expected "2 TT, 1 U", and we crash when level lowering TT<int>. Ultimately the problem is that tsubst_lambda_expr does things in the wrong order: we ought to substitute (and install) the in-scope template parameters _before_ substituting anything that may use those template parameters (such as the function type of a generic lambda). This patch corrects this substitution order. PR c++/109651 gcc/cp/ChangeLog: * pt.cc (coerce_template_args_for_ttp): Mention we can hit the current_template_parms fallback when level-lowering a bound ttp. (tsubst_template_decl): Add lambda_tparms parameter. Prefer to use lambda_tparms instead of substituting DECL_TEMPLATE_PARMS. (tsubst_decl) <case TEMPLATE_DECL>: Pass NULL_TREE as lambda_tparms to tsubst_template_decl. (tsubst_lambda_expr): For a generic lambda, substitute DECL_TEMPLATE_PARMS and set current_template_parms to it before substituting the function type. Pass the substituted DECL_TEMPLATE_PARMS as lambda_tparms to tsubst_template_decl. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/lambda-generic-ttp1.C: New test. * g++.dg/cpp2a/lambda-generic-ttp2.C: New test.
