Quuxplusone added inline comments.
================
Comment at:
clang-tools-extra/test/clang-tidy/checkers/google-readability-casting.cpp:342
+ auto w = new int(x);
+}
----------------
salman-javed-nz wrote:
> carlosgalvezp wrote:
> > carlosgalvezp wrote:
> > > Quuxplusone wrote:
> > > > What about
> > > > ```
> > > > template<class T> T foo(int i) { return T(i); }
> > > > int main() {
> > > > foo<std::vector<int>>(); // valid, OK(!)
> > > > foo<double>(); // valid, not OK
> > > > }
> > > > ```
> > > > What about
> > > > ```
> > > > struct Widget { Widget(int); };
> > > > using T = Widget;
> > > > using U = Widget&;
> > > > int i = 42;
> > > > Widget t = T(i); // valid, OK?
> > > > Widget u = U(i); // valid C++, should definitely not be OK
> > > > ```
> > > > https://quuxplusone.github.io/blog/2020/01/22/expression-list-in-functional-cast/
> > > Good point, thanks! I've added the first one to the unit test.
> > >
> > > Regarding the second check, I'm not sure if it's the scope of this check.
> > > This check does not care whether the constructor of the class is implicit
> > > or not - if you use a class type, then you are calling the constructor so
> > > it's fine. Same goes when it's a reference - in my opinion this check is
> > > not concerned with that.
> > >
> > > I definitely see the problems that can arise from the example that you
> > > posted, but maybe it fits better as a separate check in the `bugprone`
> > > category? This check (`google-readability-casting`) is focused only about
> > > avoiding C-style casting, i.e. it's a readability/style/modernize matter
> > > IMO. If cpplint is not diagnosing that, I don't think this check should
> > > either.
> > It seems I should be able to just add the second example as a test and
> > clang-tidy would warn but, what should be the fixit for it? A
> > `static_cast<U>` would lead to compiler error (which I personally would
> > gladly take, but I don't know in general if we want clang-tidy to "fix"
> > code leading to compiler errors"). Adding an ad-hoc message for this
> > particular error seems out of the scope of a "readability" check.
> >
> > What do you guys think?
> > It seems I should be able to just add the second example as a test and
> > clang-tidy would warn but, what should be the fixit for it?
>
> If I run the second example, but with old style C casts instead:
>
> Input:
> ```lang=cpp
> struct Widget { Widget(int); };
> using T = Widget;
> using U = Widget&;
> int i = 42;
> Widget t = (T)(i);
> Widget u = (U)(i);
> ```
>
> Output after fixits:
> ```lang=cpp
> struct Widget { Widget(int); };
> using T = Widget;
> using U = Widget&;
> int i = 42;
> Widget t = T(i);
> Widget u = (U)(i);
> ```
>
> I guess the fix `Widget t = T(i);` is OK as it is covered by this exception:
> >You may use cast formats like `T(x)` only when `T` is a class type.
>
> For the `Widget u = (U)(i);` line, clang-tidy has warned about it but not
> offered a fix.
> What would be the right fixit for that anyway?
> `Widget u = U(i); --> Widget u = static_cast<T>(i);` ?
No, this is a reinterpret_cast, so it would be
```
Widget u = reinterpret_cast<U>(i);
```
at least in C++. I don't know about C, but I imagine the problem doesn't come
up.
(If the programmer looks at this line and says "oh geez, that's wrong," well,
he'll either fix it or file a task to revisit weird reinterpret_casts in the
codebase. If the programmer thinks the cast is //correct//, then personally I'd
hope he rewrites it as `Widget u = *reinterpret_cast<Widget*>(&i);` for
clarity, but that's not a clang-tidy issue.)
Relevant: "fixits versus suppression mechanisms"
https://quuxplusone.github.io/blog/2020/09/02/wparentheses/ `reinterpret_cast`
is a suppression mechanism; I infer that you're casting about for a fixit,
which won't exist in this case.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D114427/new/
https://reviews.llvm.org/D114427
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