| Issue |
83474
|
| Summary |
[clang] False positive "-Wunsequenced" for C++20 parenthesized initializer lists
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
vapdrs
|
Clang 17.0.6 and the latest git/main branch will issue "-Wunsequenced" for the following code sample,
```c++
int val = 0;
struct S { int a; int b; };
int paren_list_init[](val++, val++);
int direct_list_init[]{val++, val++};
S paren_list_init_s(val++, val++);
S direct_list_init_s{val++, val++};
```
for only the C++20 parenthesized initializer lists, even though both are sequenced operations.
```
$ guix shell clang -- clang -c -o /dev/null -Wunsequenced -std=c++20 test.cpp
test.cpp:4:26: warning: multiple unsequenced modifications to 'val' [-Wunsequenced]
4 | int paren_list_init[](val++, val++);
| ^ ~~
test.cpp:7:24: warning: multiple unsequenced modifications to 'val' [-Wunsequenced]
7 | S paren_list_init_s(val++, val++);
| ^ ~~
2 warnings generated.
```
I believe this to be a false positive because the C++20 parenthesized initializer lists added in [p0960r3](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0960r3.html) explicitly state that the values and sides effects are explicitly sequenced, and provides the ordering. See C++20 [decl.init]p17.5 and [decl.init]p17.6.2.2, or the latest draft [here](https://www.eel.is/c++draft/dcl.init#general-16.5) and [here](https://www.eel.is/c++draft/dcl.init#general-16.6.2.2)
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