[CMake] Debian packaging auto-dependency bugfix

[Jess Morecroft]

Hi all,

I experienced problems recently trying to use the CPack DEB packager 
with components and wanted to share my solution (thanks partly to Eric 
Noulard). The problem was with dependency generation in the Debian 
control file using the CPACK_DEBIAN_PACKAGE_SHLIBS flag. Dependencies 
would be generated, however each component would be incorrectly assigned 
all previously processed components' dependencies on top of its own. 
This would occur regardless of whether the user explicitly set any 
(additional) dependencies via CPACK_DEBIAN_PACKAGE_DEPENDS.

eg. 3 components,
     1 has dependencies A, B, C, 3
     2 has dependencies D, E, F, 3
     3 has dependencies G
relevant config:
set(CPACK_COMPONENTS_IGNORE_GROUPS TRUE)
set(CPACK_DEB_COMPONENT_INSTALL TRUE)
set(CPACK_DEBIAN_PACKAGE_SHLIBDEPS TRUE)

We have no way of expressing dependencies between components for the 
purposes of Debian packaging (so far as I know) so 1 and 2 depending on 
3 is not achievable. That aside, if processed 1 then 2, then 3, the 
resultant package 1 would depend on A, B, C, package 2 (incorrectly) on 
A, B, C, D, E, F and package 3 (incorrectly) on A, B, C, D, E, F, G.

To fix I patched the CPackDeb.cmake script as follows, introducing new 
per-component user-defined dependency variable 
CPACK_DEB_<component>_PACKAGE_DEPENDS, which should be used over 
CPACK_DEBIAN_PACKAGE_DEPENDS if components are being used.

214,218c214,226
<     IF (CPACK_DEBIAN_PACKAGE_DEPENDS)
<       SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}, ${CPACK_DEBIAN_PACKAGE_DEPENDS}")
<     ELSE (CPACK_DEBIAN_PACKAGE_DEPENDS)
<       SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}")
<     ENDIF (CPACK_DEBIAN_PACKAGE_DEPENDS)
---
 >     IF(CPACK_DEB_PACKAGE_COMPONENT)
 >       IF (CPACK_DEB_${CPACK_DEB_PACKAGE_COMPONENT}_PACKAGE_DEPENDS)
 >         SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}, 
${CPACK_DEB_${CPACK_DEB_PACKAGE_COMPONENT}_PACKAGE_DEPENDS}")
 >       ELSE (CPACK_DEB_${CPACK_DEB_PACKAGE_COMPONENT}_PACKAGE_DEPENDS)
 >         SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}")
 >       ENDIF (CPACK_DEB_${CPACK_DEB_PACKAGE_COMPONENT}_PACKAGE_DEPENDS)
 >     ELSE (CPACK_DEB_PACKAGE_COMPONENT)
 >       IF (CPACK_DEBIAN_PACKAGE_DEPENDS)
 >         SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}, ${CPACK_DEBIAN_PACKAGE_DEPENDS}")
 >       ELSE (CPACK_DEBIAN_PACKAGE_DEPENDS)
 >         SET (CPACK_DEBIAN_PACKAGE_DEPENDS 
"${CPACK_DEBIAN_PACKAGE_AUTO_DEPENDS}")
 >       ENDIF (CPACK_DEBIAN_PACKAGE_DEPENDS)
 >     ENDIF (CPACK_DEB_PACKAGE_COMPONENT)

This config then will do the trick, also allowing 1 and 2's dependency 
on 3 to be expressed:

set(CPACK_COMPONENTS_IGNORE_GROUPS TRUE)
set(CPACK_DEB_COMPONENT_INSTALL TRUE)
set(CPACK_DEB_1_PACKAGE_DEPENDS "myproject-3")
set(CPACK_DEB_2_PACKAGE_DEPENDS "myproject-3")
set(CPACK_DEBIAN_PACKAGE_SHLIBDEPS TRUE)

I shall submit a bug report with advised patch in the next few days.

Incidentally, I did stumble across another "bug" with the Debian 
packager unable to deal with components not containing any exe or lib 
files. Fortunately my final project layout avoided this scenario, but 
you've been warned!

Regards,
Jess