Here, we were trying to start defining a template in the middle of the template parameter list for another template. Adjusting the PROCESSING_REAL_TEMPLATE_DECL_P macro to exclude this situation seems appropriate.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit f7bcdc914de03d87a99bc7ebd85fefb031028ef0 Author: Jason Merrill <ja...@redhat.com> Date: Fri Apr 6 09:07:23 2018 -0400 PR c++/85242 - ICE with class definition in template parm. * cp-tree.h (PROCESSING_REAL_TEMPLATE_DECL_P): False if processing_template_parmlist. diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index dbe34c096f0..204791e51cf 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -4719,7 +4719,8 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter) entity with its own template parameter list, and which is not a full specialization. */ #define PROCESSING_REAL_TEMPLATE_DECL_P() \ - (processing_template_decl > template_class_depth (current_scope ())) + (!processing_template_parmlist \ + && processing_template_decl > template_class_depth (current_scope ())) /* Nonzero if this VAR_DECL or FUNCTION_DECL has already been instantiated, i.e. its definition has been generated from the diff --git a/gcc/testsuite/g++.dg/template/error58.C b/gcc/testsuite/g++.dg/template/error58.C new file mode 100644 index 00000000000..cede1c94887 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/error58.C @@ -0,0 +1,8 @@ +// PR c++/85242 + +namespace N +{ + struct A {}; +} + +template<struct N::A {}> void foo(); // { dg-error "" }