[CMake] Secret precompiled header support?

[Robert Dailey]

No one has anything to say about this?

On Wed, May 9, 2012 at 1:32 PM, Robert Dailey <rcdailey.lists at gmail.com>wrote:

> To my knowledge there are no dedicated target properties or commands that
> allow one to easily add precompiled headers support to a target. In my
> case, I'm generating for visual studio and I have the following that I can
> use to enable precompiled headers:
>
> macro( _precompiled_headers PrecompiledHeader PrecompiledSource SourcesVar
> )
> if( MSVC )
> get_filename_component( PrecompiledBasename ${PrecompiledHeader} NAME_WE )
>  set( PrecompiledBinary
> "${CMAKE_CURRENT_BINARY_DIR}/${PrecompiledBasename}.pch" )
> set( Sources ${${SourcesVar}} )
>
> set_property(
> SOURCE ${PrecompiledSource} APPEND_STRING PROPERTY
>  COMPILE_FLAGS "/Yc\"${PrecompiledHeader}\" /Fp\"${PrecompiledBinary}\""
> )
>
> set_property(
> SOURCE ${PrecompiledSource} APPEND PROPERTY
>  OBJECT_OUTPUTS "${PrecompiledBinary}"
> )
>  set_property(
> SOURCE ${Sources} APPEND_STRING PROPERTY
> COMPILE_FLAGS "/Yu\"${PrecompiledHeader}\" /Fp\"${PrecompiledBinary}\""
>  )
>  set_property(
>  SOURCE ${Sources} APPEND PROPERTY
> OBJECT_DEPENDS "${PrecompiledBinary}"
>  )
> else()
> message( "Precompiled header support not provided for this platform" )
>  endif()
>  # Add precompiled header to SourcesVar
>  list( APPEND ${SourcesVar} ${PrecompiledSource} )
> endmacro()
>
> The one interesting thing I have noticed is the way these compile flags
> translate to actual vcproj output:
>
> <FileConfiguration
> Name="MinSizeRel|Win32">
>  <Tool
> Name="VCCLCompilerTool"
>
> ForcedIncludeFiles="C:/Code/work/cmake-decomp/cmake/files/source/hash_map_hack.hpp;StdAfx.cpp"
>
> PrecompiledHeaderFile="C:/Code/work/cmake-decomp/build-vc9/server/exchange/tools/uploadlog/StdAfx.pch"
> PrecompiledHeaderThrough="StdAfx.h"
>  UsePrecompiledHeader="2"
>
> AdditionalDependencies="C:\Code\work\cmake-decomp\build-vc9\server\exchange\tools\uploadlog\StdAfx.pch"
>  />
>
> CMake seems to do more than just add them as general compiler flags, it
> seems to know exactly which attributes in the VCPROJ XML are mapped to
> their respective command line alternatives, and uses the appropriate ones.
> If this is true, why do we not have a dedicated target & source file
> property that I can use to enable precompiled headers instead of using
> these command line strings directly? Am I misunderstanding something?
>
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