[Bug c++/98803] New: [C++20] ICE on invalid code with checked build [in synthesize_implicit_template_parm, at cp/parser.c:45335]

[dimitri.gorokhovik at free dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98803

            Bug ID: 98803
           Summary: [C++20] ICE on invalid code with checked build [in
                    synthesize_implicit_template_parm, at
                    cp/parser.c:45335]
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dimitri.gorokhovik at free dot fr
  Target Milestone: ---

Not sure whether ICEs from tree-check choking on error_mark should be
submitted, but here is:


template <typename> concept Defined = true;

template <auto, auto> struct entry {};

template <Defined auto d, Undefined auto u>
constexpr auto matches (entry <d, u>, Atom auto b) { return d == b; };


compiling with 'g++ -std=c++20' from 11.0.0 20210123 produces:

bug-12.cpp:6:27: error: ‘Undefined’ has not been declared
    6 | template <Defined auto d, Undefined auto u>
      |                           ^~~~~~~~~
bug-12.cpp:6:27: error: two or more data types in declaration of ‘u’
bug-12.cpp:7:35: error: ‘u’ was not declared in this scope
    7 | constexpr auto matches (entry <d, u>, Atom auto b) { return d == b; };
      |                                   ^
bug-12.cpp:7:36: error: template argument 2 is invalid
    7 | constexpr auto matches (entry <d, u>, Atom auto b) { return d == b; };
      |                                    ^
bug-12.cpp:7:39: error: ‘Atom’ has not been declared
    7 | constexpr auto matches (entry <d, u>, Atom auto b) { return d == b; };
      |                                       ^~~~
bug-12.cpp:7:49: internal compiler error: tree check: expected tree that
contains ‘decl common’ structure, have ‘error_mark’ in
synthesize_implicit_template_parm, at cp/parser.c:45335
    7 | constexpr auto matches (entry <d, u>, Atom auto b) { return d == b; };
      |                                                 ^
0x837a8f tree_contains_struct_check_failed(tree_node const*,
tree_node_structure_enum, char const*, int, char const*)
        ../../src/gcc/tree.c:9986
0x6b0fa0 contains_struct_check(tree_node*, tree_node_structure_enum, char
const*, int, char const*)
        ../../src/gcc/tree.h:3452
0x6b0fa0 synthesize_implicit_template_parm
        ../../src/gcc/cp/parser.c:45335
0xa94bad cp_parser_simple_type_specifier
        ../../src/gcc/cp/parser.c:18648
0xa7332d cp_parser_type_specifier
        ../../src/gcc/cp/parser.c:18457
0xa74329 cp_parser_decl_specifier_seq
        ../../src/gcc/cp/parser.c:15003
0xa8efce cp_parser_parameter_declaration
        ../../src/gcc/cp/parser.c:23693
0xa8f9a2 cp_parser_parameter_declaration_list
        ../../src/gcc/cp/parser.c:23510
0xa8fdf1 cp_parser_parameter_declaration_clause
        ../../src/gcc/cp/parser.c:23437
0xa80f33 cp_parser_direct_declarator
        ../../src/gcc/cp/parser.c:22086
0xa80f33 cp_parser_declarator
        ../../src/gcc/cp/parser.c:21949
0xa97f98 cp_parser_init_declarator
        ../../src/gcc/cp/parser.c:21447
0xa9edab cp_parser_single_declaration
        ../../src/gcc/cp/parser.c:30432
0xa9ef16 cp_parser_template_declaration_after_parameters
        ../../src/gcc/cp/parser.c:30004
0xa9f6c0 cp_parser_explicit_template_declaration
        ../../src/gcc/cp/parser.c:30270
0xaa1e09 cp_parser_declaration
        ../../src/gcc/cp/parser.c:14009
0xaa27ec cp_parser_toplevel_declaration
        ../../src/gcc/cp/parser.c:14107
0xaa27ec cp_parser_translation_unit
        ../../src/gcc/cp/parser.c:4936
0xaa27ec c_parse_file()
        ../../src/gcc/cp/parser.c:45170
0xbc538d c_common_parse_file()
        ../../src/gcc/c-family/c-opts.c:1211
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