Assimp's CMake config files are malformed

[Silvio Traversaro]

The CMake config files shipped with the libassimp-dev package in Ubuntu 20.04 are malformed, and export the wrong include directories.

I prepare a minimal reproducible example in https://gist.github.com/traversaro/1046013d018ff998fac1cea6987be7e0 .

To reproduce it, just compile it as:
git clone https://gist.github.com/traversaro/1046013d018ff998fac1cea6987be7e0
cd 1046013d018ff998fac1cea6987be7e0
chmod +x build.sh
./build.sh

This will fail with the message:
~~~
-- Detecting CXX compile features - done
CMake Warning (dev) at /usr/lib/x86_64-linux-gnu/cmake/assimp-5.0/assimpTargets.cmake:54 (if):
  if given arguments:

    "ON"

  An argument named "ON" appears in a conditional statement. Policy CMP0012
  is not set: if() recognizes numbers and boolean constants. Run "cmake
  --help-policy CMP0012" for policy details. Use the cmake_policy command to
  set the policy and suppress this warning.
Call Stack (most recent call first):
  /usr/lib/x86_64-linux-gnu/cmake/assimp-5.0/assimp-config.cmake:1 (include)
  CMakeLists.txt:4 (find_package)
This warning is for project developers. Use -Wno-dev to suppress it.

-- Configuring done
CMake Error in CMakeLists.txt:
  Imported target "assimp::assimp" includes non-existent path

    "/usr/lib/include"

  in its INTERFACE_INCLUDE_DIRECTORIES. Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.

CMake Error in CMakeLists.txt:
  Imported target "assimp::assimp" includes non-existent path

    "/usr/lib/include"

  in its INTERFACE_INCLUDE_DIRECTORIES. Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.
~~~

Downstream bug: https://github.com/robotology/idyntree/issues/693 .

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Paul Keir (pkeir)]

This affects me too, on Ubuntu 20.10. I actually noticed it first when using Vcpkg (on Ubuntu).

[IOhannes m zmoelnig (umlaeute)]

this was fixed with assimp-5.1 which will be part of Ubuntu starting with jammy (22.04)