Bug#894656: libpcl-dev 1.8.0 exports the Qt5::Widgets target but doesn't provide it

[Mikael Arguedas]

Package: pcl

Version: 1.8.0+dfsg1-3


When I find_package PCL, I'm unable to create shared libraries linking
against PCL due to the target "Qt5::Widgets" being exported.

This has been fixed in pcl 1.8.1 by adding a dependency on
libvtk6-qt-dev in the libpcl-dev package. 1.8.0 is missing that
dependency.


I am using Debian GNU/Linux 9.4 (stretch), kernel 4.13.0-36-generic,
libc6 2.24-11+deb9u3.

libpcl-dev package information:

Architecture: amd64
Source: pcl (1.8.0+dfsg1-3)
Version: 1.8.0+dfsg1-3+b2
Depends: libboost-all-dev, libeigen3-dev, libflann-dev, libvtk6-dev,
libqhull-dev, libopenni-dev, libopenni2-dev, libpcl-apps1.8 (=
1.8.0+dfsg1-3+b2), libpcl-common1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-features1.8 (= 1.8.0+dfsg1-3+b2), libpcl-filters1.8 (=
1.8.0+dfsg1-3+b2), libpcl-io1.8 (= 1.8.0+dfsg1-3+b2), libpcl-kdtree1.8
(= 1.8.0+dfsg1-3+b2), libpcl-keypoints1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-ml1.8 (= 1.8.0+dfsg1-3+b2), libpcl-octree1.8 (=
1.8.0+dfsg1-3+b2), libpcl-outofcore1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-people1.8 (= 1.8.0+dfsg1-3+b2), libpcl-recognition1.8 (=
1.8.0+dfsg1-3+b2), libpcl-registration1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-sample-consensus1.8 (= 1.8.0+dfsg1-3+b2), libpcl-search1.8 (=
1.8.0+dfsg1-3+b2), libpcl-segmentation1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-stereo1.8 (= 1.8.0+dfsg1-3+b2), libpcl-surface1.8 (=
1.8.0+dfsg1-3+b2), libpcl-tracking1.8 (= 1.8.0+dfsg1-3+b2),
libpcl-visualization1.8 (= 1.8.0+dfsg1-3+b2)

Reproducible example:

1. mkdir /tmp/test_pcl_bug

2. cd /tmp/test_pcl_bug && mkdir src && mkdir build

3. touch CMakelists.txt

4. add the following content to the CMakeLists.txt

CMakeLists.txt:
```
cmake_minimum_required(VERSION 2.8)
project(bug_pcl_qt)

find_package(PCL REQUIRED)

message(STATUS "${PCL_LIBRARIES}")
message(STATUS "${PCL_INCLUDE_DIRS}")

include_directories("${PCL_INCLUDE_DIRS}")
add_library(test_pcl src/test.cpp)

target_include_directories(test_pcl SYSTEM PUBLIC ${PCL_INCLUDE_DIRS})
target_link_libraries(test_pcl ${PCL_LIBRARIES})

```

5. touch src/test.cpp
6. add the following content to the src/test.cpp file (code copied from
http://pointclouds.org/documentation/tutorials/writing_pcd.php#writing-pcd)

```
#include <iostream>
#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>

int foo (int argc, char** argv)
{
  pcl::PointCloud<pcl::PointXYZ> cloud;

    // Fill in the cloud data
  cloud.width    = 5;
  cloud.height   = 1;
  cloud.is_dense = false;
  cloud.points.resize (cloud.width * cloud.height);

  for (size_t i = 0; i < cloud.points.size (); ++i)
  {
    cloud.points[i].x = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].y = 1024 * rand () / (RAND_MAX + 1.0f);
    cloud.points[i].z = 1024 * rand () / (RAND_MAX + 1.0f);
  }

  pcl::io::savePCDFileASCII ("test_pcd.pcd", cloud);
  std::cerr << "Saved " << cloud.points.size () << " data points to
test_pcd.pcd." << std::endl;

  for (size_t i = 0; i < cloud.points.size (); ++i)
    std::cerr << "    " << cloud.points[i].x << " " << cloud.points[i].y <<
" " << cloud.points[i].z << std::endl;

  return (0);
}


```

7. cd /tmp/test_pcl_bug/build
8. cmake -DBUILD_SHARED_LIBS=ON ..
8) throws the following warning:
```
CMake Warning (dev) at CMakeLists.txt:10 (add_library):
  Policy CMP0028 is not set: Double colon in target name means ALIAS or
  IMPORTED target.  Run "cmake --help-policy CMP0028" for policy details.
  Use the cmake_policy command to set the policy and suppress this warning.

  Target "test_pcl" links to target "Qt5::Widgets" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target,
or
  an ALIAS target is missing?
```

9. make

9) fails with error message:
```
[100%] Linking CXX shared library libtest_pcl.so
/usr/bin/ld: cannot find -lQt5::Widgets
collect2: error: ld returned 1 exit status
CMakeFiles/test_pcl.dir/build.make:364: recipe for target 'libtest_pcl.so'
failed
make[2]: *** [libtest_pcl.so] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/test_pcl.dir/all'
failed
make[1]: *** [CMakeFiles/test_pcl.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
```

Installing "libvtk6-qt-dev" and repeating the steps above fixes the issue.
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