r267534 - [MSVC] PR27337: allow static_cast from private base to derived for WTL
David Majnemer via cfe-commits
cfe-commits at lists.llvm.org
Tue Apr 26 19:04:58 PDT 2016
Visual Studio 2015 (19.00.23720.0) reports:
error C2243: 'static_cast': conversion from 'B *' to 'A *' exists, but is
inaccessible
On Tue, Apr 26, 2016 at 6:33 PM, Richard Smith via cfe-commits <
cfe-commits at lists.llvm.org> wrote:
> As noted in PR27337, this only occurs in one WTL sample, and we have no
> evidence that it actually occurs in real code. Have you seen uses of this
> in the wild? We generally don't want to add compatibility for MSVC bugs
> unless there's some real-world motivation.
>
>
> On Tue, Apr 26, 2016 at 2:21 AM, Dmitry Polukhin via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
>> Author: dpolukhin
>> Date: Tue Apr 26 04:21:17 2016
>> New Revision: 267534
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=267534&view=rev
>> Log:
>> [MSVC] PR27337: allow static_cast from private base to derived for WTL
>>
>> MSVC doesn't report even warning for cast from private base class to
>> derived.
>>
>> Differential Revision: http://reviews.llvm.org/D19477
>>
>> Added:
>> cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp (with props)
>> Modified:
>> cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> cfe/trunk/lib/Sema/SemaCast.cpp
>>
>> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=267534&r1=267533&r2=267534&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Tue Apr 26
>> 04:21:17 2016
>> @@ -5764,6 +5764,9 @@ def err_static_downcast_via_virtual : Er
>> "cannot cast %0 to %1 via virtual base %2">;
>> def err_downcast_from_inaccessible_base : Error<
>> "cannot cast %select{private|protected}2 base class %1 to %0">;
>> +def ext_ms_downcast_from_inaccessible_base : ExtWarn<
>> + "casting from %select{private|protected}2 base class %1 to derived
>> class %0 is a Microsoft extension">,
>> + InGroup<MicrosoftCast>;
>> def err_upcast_to_inaccessible_base : Error<
>> "cannot cast %0 to its %select{private|protected}2 base class %1">;
>> def err_bad_dynamic_cast_not_ref_or_ptr : Error<
>>
>> Modified: cfe/trunk/lib/Sema/SemaCast.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaCast.cpp?rev=267534&r1=267533&r2=267534&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaCast.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaCast.cpp Tue Apr 26 04:21:17 2016
>> @@ -1344,10 +1344,11 @@ TryStaticDowncast(Sema &Self, CanQualTyp
>> }
>>
>> if (!CStyle) {
>> - switch (Self.CheckBaseClassAccess(OpRange.getBegin(),
>> - SrcType, DestType,
>> - Paths.front(),
>> -
>> diag::err_downcast_from_inaccessible_base)) {
>> + unsigned Diag = Self.getLangOpts().MSVCCompat
>> + ? diag::ext_ms_downcast_from_inaccessible_base
>> + : diag::err_downcast_from_inaccessible_base;
>> + switch (Self.CheckBaseClassAccess(OpRange.getBegin(), SrcType,
>> DestType,
>> + Paths.front(), Diag)) {
>> case Sema::AR_accessible:
>> case Sema::AR_delayed: // be optimistic
>> case Sema::AR_dependent: // be optimistic
>>
>> Added: cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp?rev=267534&view=auto
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp (added)
>> +++ cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp Tue Apr 26 04:21:17 2016
>> @@ -0,0 +1,40 @@
>> +// RUN: %clang_cc1 -fsyntax-only -fms-compatibility -verify %s
>> +// RUN: %clang_cc1 -fsyntax-only -DNO_MS_COMPATIBILITY -verify %s
>> +
>> +// Minimal reproducer.
>> +class A {};
>> +class B : A {}; // expected-note 2 {{implicitly declared private here}}
>> +
>> +B* foo(A* p) {
>> + return static_cast<B*>(p);
>> +#ifdef NO_MS_COMPATIBILITY
>> + // expected-error at -2 {{cannot cast private base class 'A' to 'B'}}
>> +#else
>> + // expected-warning at -4 {{casting from private base class 'A' to
>> derived class 'B' is a Microsoft extension}}
>> +#endif
>> +}
>> +
>> +A* bar(B* p) {
>> + return static_cast<A*>(p); // expected-error {{cannot cast 'B' to its
>> private base class 'A'}}
>> +}
>> +
>> +// from atlframe.h
>> +template <class T>
>> +class CUpdateUI {
>> +public:
>> + CUpdateUI() {
>> + T* pT = static_cast<T*>(this);
>> +#ifdef NO_MS_COMPATIBILITY
>> + // expected-error at -2 {{cannot cast private base class}}
>> +#else
>> + // expected-warning at -4 {{casting from private base class
>> 'CUpdateUI<CMDIFrame>' to derived class 'CMDIFrame' is a Microsoft
>> extension}}
>> +#endif
>> + }
>> +};
>> +
>> +// from sample WTL/MDIDocVw (mainfrm.h
>> +class CMDIFrame : CUpdateUI<CMDIFrame> {};
>> +// expected-note at -1 {{implicitly declared private here}}
>> +// expected-note at -2 {{in instantiation of member function}}
>> +
>> +CMDIFrame wndMain;
>>
>> Propchange: cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp
>>
>> ------------------------------------------------------------------------------
>> svn:eol-style = native
>>
>> Propchange: cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp
>>
>> ------------------------------------------------------------------------------
>> svn:keywords = "Author Date Id Rev URL"
>>
>> Propchange: cfe/trunk/test/SemaCXX/ext_ms_downcast.cpp
>>
>> ------------------------------------------------------------------------------
>> svn:mime-type = text/plain
>>
>>
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>>
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