Direct, indi­rect and explic­it depen­den­cies in progams/ports

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.

Some def­i­n­i­tions:

  • 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:

  1. 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.
  2. 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.

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