[Bug c++/89995] New: Misleading error message 'this' was not captured for this lambda function

[gabriel.aubut-lussier at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89995

            Bug ID: 89995
           Summary: Misleading error message 'this' was not captured for
                    this lambda function
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabriel.aubut-lussier at outlook dot com
  Target Milestone: ---

The error message given when 'this' cannot be captured is misleading in the
sense that it points the user to the lambda that fails to capture 'this' rather
than raise questions about why it fails to do so.

The icc compiler does the best job of giving context with this error. MSVC also
displays a bit more information. Clang has the worst offender. GCC could use a
bit of improvement. Aiming for an error message that is closer to icc seems
like the ideal solution. The error message given by icc is the following:
error: this enclosing-function local variable cannot be referenced in this
lambda body because an enclosing lambda does not allow implicit captures

Godbolt : https://gcc.godbolt.org/z/rmefHT
Sample code for the issue:

struct S
{
    void f() {
        []() {
            [this]() {

            }();
        }();
    }
};

int main()
{
    S s;
    s.f();
}