[Bug c++/79488] New: [7 Regression] ICE from lambda that has invalid return type

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79488

            Bug ID: 79488
           Summary: [7 Regression] ICE from lambda that has invalid return
                    type
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Keywords: ice-on-invalid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This is reduced from Bug 79486, where a bug in the libstdc++ code could trigger
this ICE.

Without the weakref or the 'virtual' keyword there's no ICE.


int f();
static int g __attribute__((__weakref__("f")));

template <typename Fn> struct res {
  static Fn val();
  using type = decltype(val()());
};

template <typename Fn> struct A {
  template <typename T> void set_result(T) {}

  virtual void run() {
    auto boundfn = []() -> typename res<Fn>::type{};
    set_result(boundfn);
  }
};

struct F {
  void operator()() &;
};

A<F> t;


r.cc: In instantiation of 'struct res<F>':
r.cc:13:46:   required from 'struct A<Fn>::run() [with Fn = F]::<lambda>'
r.cc:13:10:   required from 'void A<Fn>::run() [with Fn = F]'
r.cc:22:7:   required from here
r.cc:6:30: error: no match for call to '(F) ()'
   using type = decltype(val()());
                         ~~~~~^~
r.cc:19:8: note: candidate: void F::operator()() & <near match>
   void operator()() &;
        ^~~~~~~~
r.cc:19:8: note:   passing 'F' as 'this' argument discards qualifiers
r.cc:10:30: error: 'void A<Fn>::set_result(T) [with T = A<Fn>::run() [with Fn =
F]::<lambda>; Fn = F]', declared using local type 'A<Fn>::run() [with Fn =
F]::<lambda>', is used but never defined [-fpermissive]
   template <typename T> void set_result(T) {}
                              ^~~~~~~~~~
r.cc: In instantiation of 'void A<Fn>::set_result(T) [with T = A<Fn>::run()
[with Fn = F]::<lambda>; Fn = F]':
r.cc:12:16:   required from here
r.cc:10:30: internal compiler error: Segmentation fault
0xdbb6df crash_signal
        /home/jwakely/src/gcc/gcc/gcc/toplev.c:337
0x845d56 contains_struct_check(tree_node*, tree_node_structure_enum, char
const*, int, char const*)
        /home/jwakely/src/gcc/gcc/gcc/tree.h:3177
0x845d56 write_closure_type_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:1639
0x845d56 write_unqualified_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:1383
0x84bab7 write_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:937
0x84b95c write_local_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:2035
0x84b95c write_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:964
0x84c5a9 write_class_enum_type
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:2777
0x84c5a9 write_type
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:2195
0x84b488 write_template_args
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:2806
0x851bad write_nested_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:1063
0x84b7f7 write_name
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:976
0x850476 write_encoding
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:825
0x8524fc mangle_decl_string
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:3757
0x85274b get_mangled_id
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:3779
0x85274b mangle_decl(tree_node*)
        /home/jwakely/src/gcc/gcc/gcc/cp/mangle.c:3849
0x1063490 decl_assembler_name(tree_node*)
        /home/jwakely/src/gcc/gcc/gcc/tree.c:671
0x9a836c symbol_table::insert_to_assembler_name_hash(symtab_node*, bool)
        /home/jwakely/src/gcc/gcc/gcc/symtab.c:171
0x9ae38f cgraph_node::create(tree_node*)
        /home/jwakely/src/gcc/gcc/gcc/cgraph.c:511
0x9ae1e0 cgraph_node::get_create(tree_node*)
        /home/jwakely/src/gcc/gcc/gcc/cgraph.c:533
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