[Bug c++/84518] New: [8 Regression] ICE with lambda capturing broken variable

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84518

            Bug ID: 84518
           Summary: [8 Regression] ICE with lambda capturing broken
                    variable
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: error-recovery, ice-on-invalid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: reichelt at gcc dot gnu.org
  Target Milestone: ---

The following invalid testcase triggers an ICE on trunk:

============================
template<int> void foo()
{
  int x[=];
  [&x]{};
}

void bar()
{
  foo<0>();
}
============================

bug.cc: In function 'void foo()':
bug.cc:3:9: error: expected primary-expression before '=' token
   int x[=];
         ^
bug.cc:3:10: error: expected primary-expression before ']' token
   int x[=];
          ^
bug.cc: In instantiation of 'void foo() [with int <anonymous> = 0]':
bug.cc:9:10:   required from here
bug.cc:4:3: internal compiler error: tree check: expected class 'expression',
have 'exceptional' (error_mark) in tree_operand_check, at tree.h:3630
   [&x]{};
   ^
0x78a846 tree_class_check_failed(tree_node const*, tree_code_class, char
const*, int, char const*)
        ../../gcc/gcc/tree.c:9385
0x614d34 expr_check(tree_node*, char const*, int, char const*)
        ../../gcc/gcc/tree.h:3301
0x614d34 tree_operand_check(tree_node*, int, char const*, int, char const*)
        ../../gcc/gcc/tree.h:3630
0x614d34 build_capture_proxy(tree_node*, tree_node*)
        ../../gcc/gcc/cp/lambda.c:447
0x8d8596 start_lambda_function(tree_node*, tree_node*)
        ../../gcc/gcc/cp/lambda.c:1374
0x95a004 tsubst_lambda_expr(tree_node*, tree_node*, int, tree_node*)
        ../../gcc/gcc/cp/pt.c:17080
0x95a9e2 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../gcc/gcc/cp/pt.c:18368
0x969349 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../gcc/gcc/cp/pt.c:17130
0x969349 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc/gcc/cp/pt.c:16862
0x968ce0 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc/gcc/cp/pt.c:16079
0x9683c9 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc/gcc/cp/pt.c:16065
0x966481 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc/gcc/cp/pt.c:16346
0x965718 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc/gcc/cp/pt.c:16050
0x965718 instantiate_decl(tree_node*, bool, bool)
        ../../gcc/gcc/cp/pt.c:23406
0x98b7ab instantiate_pending_templates(int)
        ../../gcc/gcc/cp/pt.c:23522
0x8b1cab c_parse_final_cleanups()
        ../../gcc/gcc/cp/decl2.c:4720
Please submit a full bug report, [etc.]

The regression was introduced between 2017-09-26 and 2017-10-07.