MantisBT - CMake
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0015970CMakeCMakepublic2016-02-11 13:442016-06-10 14:31
jbohren 
Kitware Robot 
normalmajoralways
closedmoved 
LinuxUbuntu14.04
CMake 2.8.12.2 
 
0015970: CMake changes order of include directories when a directory is specified both as a SYSTEM and non-SYSTEM include
I ran into a problem recently where a package I was building set a SYSTEM include directory which was already a non-SYSTEM include directory imported from a dependency. When this happened, CMake dropped the non-SYSTEM directory in favor of the SYSTEM one, causing my build to fail.

According to GCC [1], it gives precedence to non-SYSTEM include directories, and specifying both for the same path produces a warning.

[1] https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html [^]
> All directories named by -isystem are searched after all directories named by -I, no matter what their order was on the command line. If the same directory is named by both -I and -isystem, the -I option is ignored. GCC provides an informative message when this occurs if -v is used.

With CMake, if both are specified, it drops the non-SYSTEM include and fails silently. For example, when building this project with any recent version of CMake on Linux, the build command is:

```bash
/usr/bin/c++ -isystem /path/to/overlay/devel/include -I/opt/ros/indigo/include -o CMakeFiles/foo.dir/foo.cpp.o -c /home/jbohren/scratch/isystem/foo.cpp
```

But with the three `incude_directory` options given in `CMakeLists.txt`, I would expect it to read:

```bash
/usr/bin/c++ -I/path/to/overlay/devel/include -I/opt/ros/indigo/include -isystem /path/to/overlay/devel/include -o CMakeFiles/foo.dir/foo.cpp.o -c /home/jbohren/scratch/isystem/foo.cpp
```

Even the following would maintain the order of the search paths, since the non-SYSTEM directories are all scanned before the SYSTEM ones:


```bash
/usr/bin/c++ -I/path/to/overlay/devel/include -I/opt/ros/indigo/include -o CMakeFiles/foo.dir/foo.cpp.o -c /home/jbohren/scratch/isystem/foo.cpp
```
Build this trivial CMake project to observe the effect: https://github.com/jbohren/isystem [^]
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Issue History
2016-02-11 13:44jbohrenNew Issue
2016-06-10 14:29Kitware RobotNote Added: 0042938
2016-06-10 14:29Kitware RobotStatusnew => resolved
2016-06-10 14:29Kitware RobotResolutionopen => moved
2016-06-10 14:29Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:31Kitware RobotStatusresolved => closed

Notes
(0042938)
Kitware Robot   
2016-06-10 14:29   
Resolving issue as `moved`.

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