https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119819
Bug ID: 119819
Summary: ICE on unexpanded template parameter pack
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eczbek.void at gmail dot com
Target Milestone: ---
https://godbolt.org/z/6bavox4Ma
```
template<int... a>
constexpr int test = (..., []<int... b> requires(b == 0) { return a; }());
static_assert(test<0> == 0);
```
```
Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/g++
Target: x86_64-linux-gnu
Configured with: ../gcc-trunk-20250415/configure
--prefix=/opt/compiler-explorer/gcc-build/staging
--enable-libstdcxx-backtrace=yes --build=x86_64-linux-gnu
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--enable-ld=yes --enable-gold=yes --enable-libstdcxx-debug
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Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.1 20250415 (experimental)
(Compiler-Explorer-Build-gcc-9f3d2506e4bf3f6baa2d8b5d2718df83c0e65cec-binutils-2.42)
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'-masm=intel' '-fno-verbose-asm' '-S' '-std=c++20' '-v' '-freport-bug'
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GNU C++20
(Compiler-Explorer-Build-gcc-9f3d2506e4bf3f6baa2d8b5d2718df83c0e65cec-binutils-2.42)
version 15.0.1 20250415 (experimental) (x86_64-linux-gnu)
compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
ignoring nonexistent directory
"/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/../../../../x86_64-linux-gnu/include"
ignoring duplicate directory
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ignoring duplicate directory
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ignoring duplicate directory
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ignoring duplicate directory
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ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring duplicate directory
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ignoring duplicate directory
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ignoring nonexistent directory
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#include "..." search starts here:
#include <...> search starts here:
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/../../../../include/c++/15.0.1
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/../../../../include/c++/15.0.1/x86_64-linux-gnu
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/../../../../include/c++/15.0.1/backward
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/include
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/include-fixed/x86_64-linux-gnu
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/x86_64-linux-gnu/15.0.1/include-fixed
/usr/local/include
/opt/compiler-explorer/gcc-trunk-20250415/bin/../lib/gcc/../../include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
Compiler executable checksum: 3fcf6743a4db937481e71ee19c98fb04
<source>: In substitution of 'template<int ...b> requires b == 0 <lambda()>
[with int ...b = {}]':
<source>:2:71: required from 'constexpr const int test<0>'
2 | constexpr int test = (..., []<int... b> requires(b == 0) { return a;
}());
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
<source>:4:15: required from here
4 | static_assert(test<0> == 0);
| ^~~~~~~
<source>:2:52: internal compiler error: unexpected expression 'b' of kind
template_parm_index
2 | constexpr int test = (..., []<int... b> requires(b == 0) { return a;
}());
| ~~~^~~~~
0x2927ef5 diagnostic_context::diagnostic_impl(rich_location*,
diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag
(*) [1], diagnostic_t)
???:0
0x293eec6 internal_error(char const*, ...)
???:0
0xb4cf20 maybe_constant_value(tree_node*, tree_node*, mce_value)
???:0
0xb5a0b8 constraints_satisfied_p(tree_node*, tree_node*)
???:0
0xd535e3 fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node*
const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool,
bool)
???:0
0xb0bcb2 build_op_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, int)
???:0
0xd74aa5 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
???:0
0xd3ce45 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
???:0
0xd1e43d instantiate_decl(tree_node*, bool, bool)
???:0
0xbd92fb mark_used(tree_node*, int)
???:0
0xd850e4 finish_id_expression(tree_node*, tree_node*, tree_node*, cp_id_kind*,
bool, bool, bool*, bool, bool, bool, bool, char const**, unsigned long)
???:0
0xcf3a23 c_parse_file()
???:0
0xe56199 c_common_parse_file()
???:0
Please submit a full bug report, with preprocessed source.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Preprocessed source stored into /tmp/cc9V5yI9.out file, please attach this to
your bugreport.
Compiler returned: 1
```
