[cfe-users] False positive -Wcomma with static_cast<void> of dependent expression

[Jonas Toth via cfe-users]

Please open a bug report instead.

Best Jonas


Am 19.10.2018 um 00:39 schrieb Mat Sutcliffe via cfe-users:
> Hello list,
>
> The following code generates one false positive of the -Wcomma
> warning: (tested with clang trunk via Matt Godbolt's Compiler
> Explorer)
>
> template <typename T>
> void foo()
> {
>     (void)42, 0;                // ok
>     static_cast<void>(42), 0;   // ok
>
>     (void)T{}, 0;               // ok
>     static_cast<void>(T{}), 0;  // false positive
> }
>
> The warning ignores comma expressions where the LHS is a CastExpr with
> a CastKind of CK_ToVoid, but the expression static_cast<void>(T{}) has
> a CastKind of CK_Dependent (confirmed with Compiler Explorer's AST
> view).
>
> I came across this when trying to do the "expander trick" without a
> fold expression or C-style cast, as in
> https://stackoverflow.com/a/30563282/1639256
>
> Thanks
> Mat
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