| Issue |
145415
|
| Summary |
[clang-tidy] `misc-redundant-_expression_` false positive with type aliases of the same type
|
| Labels |
clang-tidy,
false-positive
|
| Assignees |
|
| Reporter |
cai-lw
|
To reproduce:
```c++
#include <array>
#include <tuple>
using MonthArray = std::array<int, 12>;
using ZodiacArray = std::array<int, 12>;
static_assert(std::tuple_size<MonthArray>::value == std::tuple_size<ZodiacArray>::value);
static_assert(std::tuple_size_v<MonthArray> == std::tuple_size_v<ZodiacArray>);
```
Output:
```
<source>:7:50: warning: both sides of operator are equivalent [misc-redundant-_expression_]
7 | static_assert(std::tuple_size<MonthArray>::value == std::tuple_size<ZodiacArray>::value);
| ^
<source>:8:45: warning: both sides of operator are equivalent [misc-redundant-_expression_]
8 | static_assert(std::tuple_size_v<MonthArray> == std::tuple_size_v<ZodiacArray>);
| ^
2 warnings generated.
```
In reality `MonthArray` and `ZodiacArray` may be defined far away from each other, or even in completely unrelated modules. When we happen to use `MonthArray` and `ZodiacArray` together, a reader without enough context is likely unaware that they are the same type, and we want to use a `static_assert` to remind the reader that they do have the same `value`. (We could also use `std::same_as<MonthArray, ZodiacArray>` but sometimes we only care about their lengths in the surrounding code)
In this case comparing `MonthArray` and `ZodiacArray` shouldn't be redundant. Such expressions should only be redundant if the two types are spelled in exactly the same way.
There has been a similar issue https://github.com/llvm/llvm-project/issues/118885 where the final resolution was that comparing different macros expanding to the same constant is non-redundant. This issue is in principal similar, but regarding to type aliases instead of macros.
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