| Issue |
58080
|
| Summary |
Confusing "undefined constructor cannot be used in a constant _expression_" error in nested class
|
| Labels |
clang:diagnostics
|
| Assignees |
|
| Reporter |
zmodem
|
Consider (https://godbolt.org/z/M4sPT137a):
```
$ cat /tmp/a.cc
struct S {
static constexpr struct T {
constexpr T() {}
} t = {};
};
$ clang -c /tmp/a.cc
/tmp/a.cc:4:7: error: constexpr variable 't' must be initialized by a constant _expression_
} t = {};
^ ~~
/tmp/a.cc:4:11: note: undefined constructor 'T' cannot be used in a constant _expression_
} t = {};
^
/tmp/a.cc:3:19: note: declared here
constexpr T() {}
^
1 error generated.
```
This is confusing: the definition of the constructor is right there on line 3, clang is even pointing it out in the note.
I suppose it's considered undefined for some technical reason, and perhaps clang could explain it?
GCC is more terse but does include a hint:
```
error: 'constexpr S::T::T()' called in a constant _expression_ before its definition is complete
```
Aha, maybe it won't be complete until the end of the outermost class definition? It would be cool if the compiler could say so.
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