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From: "josephcsible at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/103091] New: Can't jump into scope of a variable with a
 nontrivial destructor in C++20
Date: Fri, 05 Nov 2021 06:29:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103091

            Bug ID: 103091
           Summary: Can't jump into scope of a variable with a nontrivial
                    destructor in C++20
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: josephcsible at gmail dot com
  Target Milestone: ---

The C++17 standard says "A program that jumps from a point where a variable
with automatic storage duration is not in scope to a point where it is in s=
cope
is ill-formed unless the variable has scalar type, class type with a trivial
default constructor and a trivial destructor, a cv-qualified version of one=
 of
these types, or an array of one of the preceding types and is declared with=
out
an initializer (11.6)."

The C++20 standard says "A program that jumps from a point where a variable
with automatic storage duration is not in scope to a point where it is in s=
cope
is ill-formed unless the variable has vacuous initialization (6.7.3)." and =
"A
variable is said to have vacuous initialization if it is default-initialized
and, if it is of class type or a (possibly multi-dimensional) array thereof,
that class type has a trivial default constructor."

Note that the C++17 standard mentions a trivial destructor here, but the C+=
+20
standard does not. Now consider this code:

struct MyStruct {
    ~MyStruct() {}
};
void foo() {
    goto x;
    MyStruct s;
x:
    return;
}

It's ill-formed in C++17, but fine in C++20. However, we currently reject t=
his
program even with -std=3Dc++20.=