MantisBT - CMake

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0014648

CMake

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public

2013-12-15 08:32

2016-06-10 14:31

Reporter

Robert·Luberda

Assigned To

Kitware Robot

Priority

high

Severity

major

Reproducibility

always

Status

closed

Resolution

moved

Platform

OS Version

Product Version

CMake 2.8.12

Target Version

Fixed in Version

Summary

0014648: Need an option to skip system headers while generating dependencies

Description

There is currently no way to tell cmake not to consider system headers while generating dependencies.

If the source file contain for example the following includes:
#include <iostream>
#include <boost/lexical_cast.hpp>
#include <tbb/atomic.hpp>
#include <unistd.h>
#include <sys/types.h>
#include "projectdir1/header1.h"
#include "projectdir2/header2.hpp"
#include "header3.h"

then CMake will try to find each of the file in the directories given by include_directories(), which has a *huge* performance impact on build process when CMake happens to actually find the files (please note that CMake does not consider some system dirs like /usr/include or /usr/include/c++/4.8 by default, and that's why the issue is somehow hidden. BTW. This is a really strange - why e.g. boost header from /usr/include are treated differently than those ones from /opt/boost-1.55.0/include?).

However the system header files do not change often, and can be ignored by CMake in a two ways:
- by ignoring the files that are #included inside the < > brackets
- by ignoring directories that are marked as SYSTEM ones during scanning for files (it could by some new property like NOT-FOR-DEPS instead of SYSTEM), just like `g++ -MM' does (and you know, g++ provides such an option for a reason...)

I assume there might be some projects that require dependencies for system headers, so that features need to be configurable. And yes, in my opinion it would be nice to have both of the features implemented, it really shouldn't be a rocket science.

The currently provided features does not fix the issue:
- include_regular_expression() is not a solution, as it's hardly possible to enumerate all non-system headers with it;
- the `fast' targets are not an option either, as they ignore all the dependencies, besides there is no `all/fast' target (see also https://blogs.kde.org/2006/08/06/working-cmake-dependency-hell [^])
- there is INCLUDE_REGEX_LINE variable in CMake sources, but it seems to be hardcoded, cannot be changed by user.

Steps To Reproduce

Take any really big C++ project using boost (and other libraries) from non-standard locations (or make sure the boost headers are visible to cmake, but using something like `include_directiories("/usr/include")') and watch the poor performance...

Additional Information

There are already two quite an old bugs about same issues:
http://public.kitware.com/Bug/view.php?id=2607 [^]
http://public.kitware.com/Bug/view.php?id=8777 [^]