[Bug c++/102272] New: rejects-valid: VLA captured in generic lambda

[simon.giesecke at snowflake dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102272

            Bug ID: 102272
           Summary: rejects-valid: VLA captured in generic lambda
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon.giesecke at snowflake dot com
  Target Milestone: ---

gcc rejects the following code:
```
int bar();

void foo() {
  char data[bar()];
  [&](auto *ptr) { data; };
}
```

saying:
```
<source>: In function 'void foo()':
<source>:6:3: error: use of deleted function
'foo()::<lambda(auto:1*)>::~<lambda>()'
    6 |   [&](auto *ptr) { data; };
      |   ^~~~~~~~~~~~~~~~~~~~~~~~
<source>:6:5: note: 'foo()::<lambda(auto:1*)>::~<lambda>()' is implicitly
deleted because the default definition would be ill-formed:
    6 |   [&](auto *ptr) { data; };
      |     ^
```

This happens in trunk and in various versions back to 8.x I tried.

With a non-generic lambda, this works.

Interestingly, it also works if the length of the VLA doesn't depend on the
result of a function call, but on a parameter of the function.

While this isn't standard C++, gcc supports VLA in C++ code generally, so I
think this should also work.