https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122833
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2025-11-27
Keywords| |ice-checking
Known to fail| |12.1.0, 12.5.0, 15.1.0
Status|UNCONFIRMED |NEW
Summary|ICE: in tsubst_expr, at |[13/14/15/16 Regression]
|cp/pt.cc with friend |ICE: in tsubst_expr, at
|default argument of a |cp/pt.cc with friend
|invocation of a lambda from |default argument of a
|a templated struct |invocation of a lambda from
| |a templated struct
Ever confirmed|0 |1
Known to work| |11.4.0
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
template <typename T>
struct A {
friend void foo(int i = []() { return 0; }()) {
}
};
A<int> a;
A<long> c;
```
The error message with release checking is bad too:
```
<source>: In instantiation of 'struct A<long int>':
<source>:9:9: required from here
9 | A<long> c;
| ^
<source>:4:29: error: taking address of rvalue [-fpermissive]
4 | friend void foo(int i = []() { return 0; }()) {
| ^~~~~~~~~~~~~~~~~~
<source>:4:47: error: no matching function for call to
'A<int>::<lambda()>::operator()(A<int>::<lambda()>*)'
4 | friend void foo(int i = []() { return 0; }()) {
| ~~~~~~~~~~~~~~~~~~^~
<source>:4:47: note: there is 1 candidate
<source>:4:29: note: candidate 1: 'A<int>::<lambda()>'
4 | friend void foo(int i = []() { return 0; }()) {
| ^
<source>:4:29: note: candidate expects 0 arguments, 1 provided
<source>:4:17: note: when instantiating default argument for call to 'void
foo(int) [with T = long int]'
4 | friend void foo(int i = []() { return 0; }()) {
| ^~~
<source>:4:17: error: redefinition of 'void foo(int)'
<source>:4:17: note: 'void foo(int)' previously declared here
Compiler returned: 1
```
In this case only the last error message has an hint of what is going on but
even then it still not obvious.
