[cfe-commits] [Patch] Warn about self-init of refs using parenthesized initializers

[Pan, Wei]

I discovered this starting from the following example

extern int &foo();
int &m([&]() { m = foo(); return m; }());

This should be also warned too.

From: cfe-commits-bounces at cs.uiuc.edu [mailto:cfe-commits-bounces at cs.uiuc.edu] On Behalf Of Richard Smith
Sent: Friday, September 28, 2012 4:15 PM
To: Jordan Rose; Richard Trieu
Cc: llvm cfe
Subject: Re: [cfe-commits] [Patch] Warn about self-init of refs using parenthesized initializers

I don't think the patch is right. My recollection of this class is (though perhaps Richard Trieu can correct me):

HandleExpr is intended to be called for the expression which is the top-level initializer of the declaration.
HandleValue is intended to be called for an expression which is "used" (either directly in the initialization of the result, or as the operand of an lvalue-to-rvalue conversion).
Visit* are called for all evaluated subexpressions (including ones we don't consider to be "used").

So... I think that we shouldn't be calling HandleExpr (nor HandleValue) from VisitParenListExpr, since it doesn't imply a use, in the required sense. I think the right way to deal with this is to add special cases for ParenListExpr and InitListExpr to HandleExpr. We also need to decide whether to warn in these cases:

int n(n); // Warn here, or is this treated like int n = n;?
int n{n}; // Warn here, or is this treated like int n = n;?


FWIW, it looks like we're missing an IgnoreParenCasts call from HandleExpr, and the IgnoreParenImpCasts call in HandleValue should be IgnoreParenCasts. We don't currently warn on cases like these, for instance:

int &r = static_cast<int&>(r);

... nor ...

struct S {} s = static_cast<S&>(s);

On Fri, Sep 28, 2012 at 9:18 AM, Jordan Rose <jordan_rose at apple.com<mailto:jordan_rose at apple.com>> wrote:
This still doesn't handle C++11 initialization, does it?

void g() {
        int &a{a};
}

Jordan


On Sep 28, 2012, at 4:05 , Hans Wennborg <hans at chromium.org<mailto:hans at chromium.org>> wrote:

> Hi,
>
> As pointed out in Wei's email [1], Clang currently fails to warn about
> self-initialized references when using parenthesized initializers:
>
>  void f() {
>    int &a(a);
>  }
>
> The attached patch fixes this. Please take a look.
>
> Thanks,
> Hans
>
> [1]. http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-September/024582.html
> <ref_self_init_parenthesized_initializers.patch>_______________________________________________
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