[Bug c++/118249] New: Misdiagnosing use of 'this' while doing class member access in constant evaluation

[barry.revzin at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118249

            Bug ID: 118249
           Summary: Misdiagnosing use of 'this' while doing class member
                    access in constant evaluation
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

Short example:

template <int I>
void f() { }

template <int N>
struct array {
    constexpr int size() const { return N; }
};

array<10> outer;

struct C {
    array<10> inner;

    void g() {
        f<outer.size()>(); // #1
        f<inner.size()>(); // #2
    }
};

Both calls to f should be okay since P2280 (unknown references in constant
expressions). gcc allows #1, but rejects #2 due to:

<source>:16:22: error: use of 'this' in a constant expression
   16 |         f<inner.size()>(); // #2
      |                      ^

But the same paper that allowed #1 also extended the rule for using `this` to
allow its use in class member access expressions, like this one. So #2 should
be okay too.