Prefix header for Makefiles

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Prefix header for Makefiles

Andrew Shaitorov
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:


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.


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CMakePrefixHeaderTest.zip (1K) Download Attachment
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Re: Prefix header for Makefiles

Jakob van Bethlehem
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 <[hidden email]> 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:


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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Re: Prefix header for Makefiles

CHEVRIER, Marc
Hi,

You are wrong. CMake, during configuration/generation phase generates dependencies over C/C++ files.
So, the simple approach to handle dependency between Cpp and h files is to let CMake handle it:

add_executable (my_exe Main.cpp)

And, that it! By default current source directory is passed to the compiler for resolving #include directives.
And for adding other directories, use command target_include_directories.

Marc

From: CMake on behalf of Jakob van Bethlehem
Date: Wednesday 26 August 2015 15:10
To: "[hidden email]"
Subject: Re: [CMake] Prefix header for Makefiles

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 <[hidden email]> 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:


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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Re: Prefix header for Makefiles

Andreas Pakulat-2
In reply to this post by Jakob van Bethlehem
Hi,

On Wed, Aug 26, 2015 at 3:10 PM, Jakob van Bethlehem <[hidden email]> wrote:
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.

Thats wrong, CMake has to parse the source files you add to a target to be able to determine its dependencies (recursively) so it can generate makefile rules that ensure that if one of the (indirectly) included headers changes the source file is recompiled. You can see this in cmDependsC.cxx in the CMake sources for C (and possibly C++) source files.

It of course does not parse the C/C++ code, it merely finds lines that start with #include or #import and figures out the absolute path of the mentioned header file based on the targets include directories.

Of course you can help CMake here by specifying all headers in the add_executable/add_library call, but that easily ends up being a maintenance nightmare for files outside of your actual project (system headers, third-party libraries etc.).

Andreas

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Re: Prefix header for Makefiles

Bill Hoffman
CMake does not really support this.  At build time CMake scans the
source files and builds the depend list.  Since your file is not
actually included it does not end up in the depend list.  To add this as
a feature you would have to put the information into DependInfo.cmake
and have cmDependsC.cxx read the information.  If you are interested, I
would suggest you come up with a patch and post it to the
cmake-developer mailing list.  You could also try the ninja generator as
it uses the compiler to compute depends and should have the correct
information.

-Bill

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