188141 - NS_CONST_CAST, NS_REINTERPRET_CAST, and NS_STATIC_CAST are not protected with parentheses properly

Status: RESOLVED INVALID

(Core :: XPCOM, defect)

Description

[Benjamin Smedberg]

The macro definitions of NS_STATIC_CAST, NS_CONST_CAST, and NS_REINTERPRET_CAST
are not protected properly with parentheses.  This can lead to
order-of-operations errors, as a trivial example:

NS_REINTERPRET_CAST(nsISupports*,somevoidpointer)->AddRef();

will fail because -> is higher precedence than the cast operator.  Patch
forthcoming.

Comment 1

[Benjamin Smedberg]

Attachment: patch to protect cast macros with parentheses

Comment 2

[Benjamin Smedberg]

Oops, accidentally clicked wrong component.

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

static_cast<T>() has the parentheses as part of the syntax -- see C++ section
5.2 clause 1.

The pattern that you say won't work is used all over the codebase (for example,
the first occurrence of NS_STATIC_CAST in nsBlockFrame.cpp), so I don't think
there are any compilers that do this wrong, either.

Comment 4

[Benjamin Smedberg]

Oops, my bad.  I misunderstood a compiler error during casting.