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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