[CMake] Secret precompiled header support?

[Robert Dailey]

Sorry, I forgot that I already had that code pasted in my original post.
Sorry for the duplicate code :)

On Mon, May 14, 2012 at 5:17 PM, Robert Dailey <rcdailey.lists at gmail.com>wrote:

> On Mon, May 14, 2012 at 4:58 PM, Bill Hoffman <bill.hoffman at kitware.com>wrote:
>>
>> For those we hard coded many of the flags into a table.  So, basically
>> for VS greater than 6, we have a table that maps flags to actual options in
>> the IDE.  There is no special per-compiled support in CMake... :)
>>
>> All it knows is that flat /Foobar == "Turn on option foobar" and creates
>> the right xml or project input file.
>
>
> Thanks for the explanation.
>
> It would be nice to have target properties for these, instead of this
> obscure mapping. It makes it difficult to figure out how exactly to append
> compiler flags. For example, I'm using set_property() with APPEND_STRING,
> and I have to make sure my spacing is correct each time I enable a
> compiler-specific feature using compiler flags. I had to use trial & error
> to determine that APPEND_STRINGS worked, but APPEND didn't for
> COMPILE_FLAGS. There's a lot of boilerplate logic that I have to deal with
> when using set_property with COMPILE_FLAGS.
>
> It would be much easier to specify some target properties instead. Or
> maybe to simplify things, we can have a compiler_flags() command that
> simplifies doing this work, if it is undesirable to have new target
> properties?
>
> Is improvement desired in this area? Is the current implementation really
> satisfactory? It doesn't exactly offer an intuitive or maintainable
> solution.
>
> Here is what I have to do right now to enable precompiled headers on MSVC:
>
> 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()
>
> I feel like CMake should offer me a higher-level way of dealing with this.
>
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