[Bug c++/101717] [12 Regression] ICE capturing static member within stateless generic lambda

["StevenSun2021 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101717

--- Comment #5 from Steven Sun <StevenSun2021 at hotmail dot com> ---
(In reply to Andrew Pinski from comment #4)
Thanks!


(In reply to myself from comment #3)

> The program seems never think of a situation "a lambda inside a lambda
> inside a NSDMI`. We need to amend the logic here.


edit to:

The program seems never think of a situation "member function call inside a
generic lambda inside a lambda inside a NSDMI`. We need to amend the logic
here.


-------------------------------------

The direct cause of failure is in g:91e534b0d

```
if (!containing_function && !COMPLETE_TYPE_P (closure))
    /* If we're parsing a lambda in a non-local class,
       we can find the fake 'this' in scope_chain.  */
    init = scope_chain->x_current_class_ptr;
```

This part of logic is to find the potential `this` since there is a (static)
member function call `f`. Refer to the following comments:

  /* For the overload resolution we need to find the actual `this`
     that would be captured if the call turns out to be to a
     non-static member function.  Do not actually capture it at this
     point.  */


// in function `build_new_method_call_1` in `gcc/cp/call.c`

-------------------------------------

As for example in comment 1:


`scope_chain->x_current_class_ptr` is correctly set when parsing 

```
[=](auto) { f(); }
```

But it was soon incorrectly set when instantiating the same lambda, i.e.
parsing

```
[=](auto) { f(); }()
``` 


This failure only affectes the potential `this` pointer inside the

```
[=](auto) { f(); }
```

But since here needs no `this` pointer, deleting that problematical
`gcc_checking_assert` is actually a potential fix for this problem.