<new>: Standard Library Header Units 'error C4430: missing type specifier' with /translateInclude

[StephanTLavavej]

Reported by @olgaark. Related to #1694.

C:\Temp\REPRO>set X_INC=D:\GitHub\STL\out\build\x86\out\inc

C:\Temp\REPRO>set X_COMMON_OPTIONS=/EHsc /nologo /W4 /MDd /Od /std:c++latest /permissive- /Zc:inline /Zc:preprocessor /c

C:\Temp\REPRO>cl %X_COMMON_OPTIONS% /ifcOutput use_ansi.h.ifc /sourceDependencies use_ansi.h.ifc.d.json /exportHeader /translateInclude /TP "%X_INC%\use_ansi.h"
use_ansi.h

C:\Temp\REPRO>cl %X_COMMON_OPTIONS% /headerUnit "%X_INC%\use_ansi.h=use_ansi.h.ifc" /ifcOutput yvals.h.ifc /sourceDependencies yvals.h.ifc.d.json /exportHeader /translateInclude /TP "%X_INC%\yvals.h"
yvals.h

C:\Temp\REPRO>cl %X_COMMON_OPTIONS% /headerUnit "%X_INC%\use_ansi.h=use_ansi.h.ifc" /headerUnit "%X_INC%\yvals.h=yvals.h.ifc" /ifcOutput exception.ifc /sourceDependencies exception.ifc.d.json /exportHeader /translateInclude /TP "%X_INC%\exception"
exception

C:\Temp\REPRO>cl %X_COMMON_OPTIONS% /headerUnit "%X_INC%\use_ansi.h=use_ansi.h.ifc" /headerUnit "%X_INC%\yvals.h=yvals.h.ifc" /headerUnit "%X_INC%\exception=exception.ifc" /ifcOutput new.ifc /sourceDependencies new.ifc.d.json /exportHeader /translateInclude /TP "%X_INC%\new"
new
D:\GitHub\STL\out\build\x86\out\inc\new(55): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
D:\GitHub\STL\out\build\x86\out\inc\new(55): error C2146: syntax error: missing ';' before identifier 'new_handler'
D:\GitHub\STL\out\build\x86\out\inc\new(56): error C2061: syntax error: identifier 'new_handler'

STL/stl/inc/new

Lines 49 to 55 in 30ac440

	#if !defined(_INC_NEW) || !defined(_MSC_EXTENSIONS)
	// handler for operator new failures
	using new_handler = void(__CLRCALL_PURE_OR_CDECL*)();
	#endif // !defined(_INC_NEW) || !defined(_MSC_EXTENSIONS)
	// FUNCTION AND OBJECT DECLARATIONS
	_CRTIMP2 new_handler __cdecl set_new_handler(_In_opt_ new_handler) noexcept;

Preprocessing <new> classically with cl %X_COMMON_OPTIONS% /P /TP "%X_INC%\new" shows that this code should expand to:

using new_handler = void(__cdecl *)();
#line 53 "D:\\GitHub\\STL\\out\\build\\x86\\out\\inc\\new"


 new_handler __cdecl set_new_handler( new_handler) noexcept;

I'm not sure what's happening with /translateInclude. (If I attempt to add /P to the /translateInclude command line, I get an ICE where <new> tries to include <exception>.)

[StephanTLavavej]

The problem appears to be with _CRTIMP2 - if I edit <new> to remove that, the error goes away.

This is defined by <crtdefs.h> as:

#ifndef _CRTIMP2
    #if defined CRTDLL2 && defined _CRTBLD
        #define _CRTIMP2 __declspec(dllexport)
    #else
        #define _CRTIMP2
    #endif
#endif

(that is, it's defined to nothing for ordinary users; it's __declspec(dllexport) when building the STL's DLL)

and it's included via the chain <new> includes <exception> includes <yvals.h> includes <crtdefs.h>:

STL/stl/inc/new

Line 11 in 30ac440

#include <exception>

STL/stl/inc/exception

Line 9 in 30ac440

#include <yvals.h>

STL/stl/inc/yvals.h

Line 13 in 30ac440

#include <crtdefs.h>

I'm guessing this is a compiler bug related to headers defining macros that expand to nothing.

[cpplearner]

It seems that a header unit does not "export" macros that were imported from another header unit.

D:\test>type a.h
#define FOO extern

D:\test>type b.h
#include "a.h"

D:\test>type c.h
#include "b.h"

FOO int x;

D:\test>set OPTIONS=/EHsc /nologo /std:c++latest /c /exportHeader /translateInclude

D:\test>cl %OPTIONS% /ifcOutput a.h.ifc a.h
a.h

D:\test>cl %OPTIONS% /ifcOutput b.h.ifc /headerUnit a.h=a.h.ifc b.h
b.h

D:\test>cl %OPTIONS% /headerUnit a.h=a.h.ifc /headerUnit b.h=b.h.ifc c.h
c.h
D:/test/c.h(3): error C2144: syntax error: 'int' should be preceded by ';'
D:/test/c.h(3): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

[cpp.import]/5 is a bit hard to interpret, but I believe that such macros should be exported.

[StephanTLavavej]

Confirmed, this is a compiler bug. Thanks for the reduced test case!

[StephanTLavavej]

Tracked by Microsoft-internal VSO-1287222 "[modules] transitive header unit imports do not import macros" and fixed by MSVC-PR-308046 in VS 2019 16.10 Preview 2.