https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104163
Bug ID: 104163
Summary: Misleading diagnostic for incompletely initialized
constinit variable
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
struct B
{
int i = 0;
};
struct C
{
void* p;
B b;
constexpr C() = default;
};
constinit C c{};
This is invalid because C::p is left uninitialized by the constructor, but
GCC's warning is confusing:
mut.C:13:13: error: 'constinit' variable 'c' does not have a constant
initializer
13 | constinit C c{};
| ^
mut.C:13:15: error: 'C{B{0}}' is not a constant expression
13 | constinit C c{};
| ^
mut.C:13:15: error: 'C()' is not a constant expression because it refers to an
incompletely initialized variable
The "'C{B{0}}' is not a constant expression" makes it look like the problem is
related to initialization of B. There is no mention of the p member. I spent
quite a bit of time trying to figure out what was wrong in a more complex,
deeply nested example.
Clang tells you exactly what's wrong:
mut.C:13:13: error: variable does not have a constant initializer
constinit C c{};
^~~
mut.C:13:1: note: required by 'constinit' specifier here
constinit C c{};
^~~~~~~~~
mut.C:13:13: note: subobject of type 'void *' is not initialized
constinit C c{};
^
mut.C:8:9: note: subobject declared here
void* p;
^
1 error generated.
The notes about the void* are clear and precise.
EDG is less clear, but at least still identifies C::p as the problem:
"mut.C", line 13: error: expression must have a constant value
constinit C c{};
^
"mut.C", line 13: note: access to uninitialized subobject (member "C::p")
constinit C c{};
^
1 error detected in the compilation of "mut.C".
