https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120155
Bug ID: 120155
Summary: ICE when lambda return type is the decltype of
statement expression
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: winmikedows at hotmail dot com
Target Milestone: ---
```cpp
void fun()
{
[](auto t) -> decltype(
({
int a = t;
})
) {};
}
```
ICEs all the way from GCC 11.1 to trunk. Interestingly, in published versions
(11.1 to 15.1) the error message is
```
<source>: In function 'void fun()':
<source>:5:21: internal compiler error: in dependent_type_p, at cp/pt.c:26813
5 | int a = t;
| ^
0x1780bf9 internal_error(char const*, ...)
???:0
0x677e40 fancy_abort(char const*, int, char const*)
???:0
0x7cc37c dependent_type_p(tree_node*)
???:0
0x6b50e5 is_rvalue_constant_expression(tree_node*)
???:0
0x7c0cab c_parse_file()
???:0
0x892aa2 c_common_parse_file()
???:0
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
```
And in trunk the error message is
```
<source>: In function 'void fun()':
<source>:5:17: internal compiler error: tree check: expected tree that contains
'decl with visibility' structure, have 'parm_decl' in start_decl, at
cp/decl.cc:6037
5 | int a = t;
| ^
0x293cc75 diagnostic_context::diagnostic_impl(rich_location*,
diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag
(*) [1], diagnostic_t)
???:0
0x2956c96 internal_error(char const*, ...)
???:0
0x9dff77 tree_contains_struct_check_failed(tree_node const*,
tree_node_structure_enum, char const*, int, char const*)
???:0
0xcfa3d3 c_parse_file()
???:0
0xe5ce99 c_common_parse_file()
???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
```
Before 10.5, this just throws an error "non-function 'a' declared as implicit
template".
Trunk also ICEs when replacing `int a = t;` with `int a = 1;`, but all
published versions do not.
Runnable example: https://godbolt.org/z/9ncd7xYWc
