[C++ Patch] PR 84588 ("[8 Regression] internal compiler error: Segmentation fault (contains_struct_check())")

[Paolo Carlini]

Hi,

in this error-recovery regression, after sensible diagnostic about "two 
or more data types in declaration..." we get confused, we issue a 
cryptic -  but useful hint to somebody working on the present bug ;) - 
"template definition of non-template" error and we finally crash. I 
think the issue here is that we want to use 
abort_fully_implicit_template as part of the error recovery done by 
cp_parser_parameter_declaration_list, when the loop is exited early 
after a cp_parser_parameter_declaration internally called 
synthesize_implicit_template_parm. Indeed, if we do that we get the same 
error recovery behavior we get for the same testcase modified to not use 
an auto parameter (likewise for related testcases):

struct a {
  void b() {}
   void c(auto = [] {
    if (a a(int int){})
      ;
  }) {}
};

Tested x86_64-linux.

Thanks, Paolo.

///////////////////

/cp
2018-04-20  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/84588
        * parser.c (cp_parser_parameter_declaration_list): When the
        entire parameter-declaration-list is erroneous maybe call
        abort_fully_implicit_template.

/testsuite
2018-04-20  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/84588
        * g++.dg/cpp1y/pr84588.C: New.
Index: cp/parser.c
===================================================================
--- cp/parser.c (revision 259516)
+++ cp/parser.c (working copy)
@@ -21358,6 +21358,8 @@ cp_parser_parameter_declaration_list (cp_parser* p
        {
          *is_error = true;
          parameters = error_mark_node;
+         if (parser->fully_implicit_function_template_p)
+           abort_fully_implicit_template (parser);
          break;
        }
 
Index: testsuite/g++.dg/cpp1y/pr84588.C
===================================================================
--- testsuite/g++.dg/cpp1y/pr84588.C    (nonexistent)
+++ testsuite/g++.dg/cpp1y/pr84588.C    (working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++14 } }
+// { dg-options "-w" }
+
+struct a {
+  void b() {}
+  void c(auto = [] {
+    if (a a(int auto){})  // { dg-error "two or more data types" }
+      ;
+  }) {}
+};