https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125679
Bug ID: 125679
Summary: [C++] ICE: Segmentation fault during error recovery
when a struct is defined in a lambda parameter list
Product: gcc
Version: 16.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: 1794833681 at qq dot com
Target Milestone: ---
The C++ frontend correctly diagnoses an invalid struct definition within a
lambda parameter list (`error: types may not be defined in parameter types`).
However, it fails to recover gracefully, resulting in a Segmentation fault in
`cc1plus` during subsequent processing (possibly related to auto return type
deduction or the variadic arguments `...`).
**Minimal Reproducible Example:**
class SystemManager {
private:
auto internal_method() {
return [](struct State {int current; int previous;}status, ...) {
};
}
public:
void run() {
auto handler = internal_method();
}
};
int main() {
SystemManager manager;
manager.run();
return 0;
}
**Command Line Arguments:**
g++ -std=c++23 source.cpp
**Tested Versions:**
* Reproduced on: x86-64 gcc 15.1 15.2
* Reproduced on: x86-64 gcc 16.1
**Compiler Output:**
<source>: In member function 'auto SystemManager::internal_method()':
<source>:4:32: error: types may not be defined in parameter types
4 | return [](struct State {int current; int
previous;}status, ...) {
| ^
g++: internal compiler error: Segmentation fault signal terminated program
cc1plus
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
**Expected Behavior:**
The compiler should emit the syntax error `types may not be defined in
parameter types` and halt compilation or gracefully recover the AST, rather
than crashing with an ICE (Segmentation fault).
