[llvm-bugs] [Bug 41586] New: [[clang::require_constant_initialization]] says a global with a defaulted trivial constructor is not constant initialized

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41586

            Bug ID: 41586
           Summary: [[clang::require_constant_initialization]] says a
                    global with a defaulted trivial constructor is not
                    constant initialized
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rnk at google.com
                CC: eric at efcs.ca, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Consider:

struct Foo { int x; };
[[clang::require_constant_initialization]] Foo obj1; // error
[[clang::require_constant_initialization]] Foo obj2{}; // ok

Clang says:

t.cpp:2:48: error: variable does not have a constant initializer
[[clang::require_constant_initialization]] Foo obj1; // error
                                               ^~~~
t.cpp:2:3: note: required by 'require_constant_initialization' attribute here
[[clang::require_constant_initialization]] Foo obj1; // error
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t.cpp:2:48: note: non-constexpr constructor 'Foo' cannot be used in a constant
expression
[[clang::require_constant_initialization]] Foo obj1; // error
                                               ^
t.cpp:1:8: note: declared here
struct Foo { int x; };
       ^

It's true that Foo's default constructor is not constexpr, it is trivial, and
it does not initialize its members. However, no dynamic initializer is needed
for obj1, which I think is the important thing that the user of this attribute
is probably looking for. Should we make an exception for this?

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