Hej Andrew,

CMake does never scan source files (as far as I know), as it is not a compiler. 
From your question it almost seem you are making this assumption, so I just 
wanted to make sure to mention at least this.

Then, for your particular issue: two things that come to my mind:
* I’d imagine you have somewhere a add_executable(main Main.cpp Prefix.h 
DependHeader.h) - as far as I can tell, the only thing that really matters, is 
that the main executable gets recompiled whenever you make a change in any of 
the headers. To put it differently, I *don’t* think you (should) need the 
OBJECT_DEPENDS.
* If you’re worried about scaling, maybe you could have a look at the file(GLOB 
) command. However, be sure to also carefully read the potential problems with 
that approach. In my current (big) project, we explicitly list each source file 
for most parts of the source tree. In practice you’re surely *not* going to add 
all 50 new files at once. It is a very simple thing to add the newly created 
file to some variable in the correct CMakeLists.txt file. You just have to 
remember to do it, it’s really not a big deal.

By the way, we’re actually using the PrecompiledHeader script - it works 
flawlessly.

Sincerely, Jakob 

> On 26 Aug 2015, at 11:48, Andrew Shaitorov <andrew.shaito...@gmail.com> wrote:
> 
> Hi All!
> 
> I have a very annoying problem with CMake Makefiles generator.
> 
> I'm using prefix header (see attached archive for minimized test).
> 
> There is one source file named Main.cpp and two header files: Prefix.h and 
> DependHeader.h. Prefix.h includes DependHeader.h and Main.cpp includes 
> Prefix.h by using prefix header compiler flag (-include for GCC/Clang and /FI 
> for MSVC):
> 
>       set_source_files_properties(Main.cpp PROPERTIES
>               COMPILE_FLAGS "-include Prefix.h"
>               OBJECT_DEPENDS ${CMAKE_CURRENT_LIST_DIR}/Prefix.h)
> 
> When I change Prefix.h, then make recompiles Main.cpp as needed. But when I 
> make a change in DependHeader.h, then no recompilation happens. Its clear for 
> me that I have to specify all depend files in OBJECT_DEPENDS option, but in 
> real project there may be a lot of depend files with nested includes. And the 
> most annoying thing is that the project compiles without any errors and may 
> just crash because of struct layout or other critical changes in depend 
> headers.
> 
> I seems like the following script have the same problem when using 
> FORCE_INCLUDE option:
> 
> https://github.com/larsch/cmake-precompiled-header/blob/master/PrecompiledHeader.cmake
>  
> <https://github.com/larsch/cmake-precompiled-header/blob/master/PrecompiledHeader.cmake>
> 
> I looked in CMake source code and didn't find a way to add Prefix.h in a list 
> for dependency scanning. Also I don't know how to run depend scanner on 
> Prefix.h in CMake script to generate a list of all depend files for 
> OBJECT_DEPENDS option.
> 
> Any advise?
> 
> Best,
> Andrew.
> 
> <CMakePrefixHeaderTest.zip>-- 
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