| Issue |
140449
|
| Summary |
Clang instantiates function templates inside a discarded statement
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
seha-bot
|
According to [[temp.inst]/5](https://eel.is/c++draft/temp.inst#5), a function template will be instantiated if its definition is required or if it changes the semantics of the program. A definition is required for a function if its name is odr-used outside a discarded statement [[basic.def.odr]/12](https://eel.is/c++draft/basic.def.odr#12.sentence-1).
However, if we write code such as:
```c++
template <typename T>
int f() {
T *ptr;
return 0;
}
int main() {
if constexpr (false) {
int x = f<int &>(); // error
}
}
```
clang attempts to instantiate `f<int &>` which forms an invalid type and the compilation fails. The instantiation should not have happened in the first place. `f<int &>` is inside a discarded statement, so its definition is not required.
Reproduction: https://godbolt.org/z/Y4M5vWcf8
There is one more example in that link which passes correctly just to show that this behavior is also inconsistent in clang. This is a regression because it worked fine in earlier versions of clang as shown in that link.
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