The discussion about direct and indirect dependencies is coming up again on the FreeBSD mailinglists. Seems I should make some blog post about it, maybe it makes this topic more findable than my postings in the mailinglists.
- A direct dependency from A to B is when program/port A uses symbols from library/port B.
- An indirect dependency from A to C is when program/port A uses symbols from library/port B but no symbols from library/port C, and library/port B uses symbols from library/port C.
- An explicit dependency from A to C is when it is a direct or indirect dependency A to C, and when the compiler-time–linker added an explicit reference to C to the program/lib of A.
Ideally we have no indirect dependencies in the explicit dependencies, only direct dependencies. Unfortunately in reality we also have indirect dependencies there. This has at least two causes:
- libtool (at least 1.x) does not (or was not) come with a hint on FreeBSD, which tells that the run-time-linker is recursively resolving dependencies.
- Some pkg–config setups list indirect dependencies as explicit dependencies (IIRC it depends if Requires.private and/or Libs.private is used in the .pc file or not; if it is used, there should be no indirect dependency appear from this software, but I am not 100% sure about this).
Three years ago I wrote /usr/ports/Tools/scripts/explicit_lib_depends.sh, it looks at the files of a given port (it needs to be installed), and prints out explicit dependencies. Because of the indirect dependencies which could be listed there, this list is not a list of ports which are real dependencies from a source code point of view, but it reflects the link-time reality. If a port C shows up there, the port which is checked needs to be rebuild in case the ABI of library/port C changes.