Sirraide wrote:
> IS a pattern folks actually use intentionally. So making this an error isn't
> something we can really do.
Right, I think I wasn’t quite awake yet earlier because for some reason I was
only thinking about the very specific use case where the `if` statement checks
if a pointer is null, but you might reasonably do this for e.g. a
`std::expected` where one branch consumes the value and the other the error.
After thinking about this some more, I wonder if it would make sense to
restrict this warning to situations where we both
1. the variable declaration is also the condition of the `if` statement, and
2. it’s very unlikely that consuming the ‘falsy’ value on the else branch would
ever be useful.
Not doing 1. would cause us to diagnose cases such as
```c++
if (Foo* x = foo(); not x) {
// ...
} else {
bar(*x); // We should not diagnose this.
}
```
And 2. should help minimise false positives; e.g. using a variable that is
known to be null in the else branch feels like a bit of a weird thing to
do—though I guess someone could reuse it by assigning to it.
> We can actually do this via
> https://clang.llvm.org/doxygen/classclang_1_1Scope.html I think instead? I
> wonder if anyone else has better ideas
Yeah, that’s more or less what I meant by ‘somehow have scope information to
figure out where a given use of it is’.
https://github.com/llvm/llvm-project/pull/156436
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