Support for self contained modules

[cladmi]

Description

I am working toward self contained modules outside of RIOT support with the same capabilities as a module defined in RIOT.

Currently adding a module may require to modify one of the global Makefile.include or Makefile.dep files and I would like to change this.

Steps

• make: process include and dep for external modules make: process include and dep for external modules #8987
• make: Add 'BUILDDEPS' variable make: Add 'BUILDDEPS' variable #9002
• Allow declaring an AUTO_INIT function from within a module directory
  • core: introduce crossfile arrays (xfa), refactored core: introduce crossfile arrays (xfa), refactored #9105
    • make: Use ld -r for intermediate linking of each module make: Use ld -r for intermediate linking of each module #8711
    • cortexm: ldscript refactor cortexm: ldscript refactor #9104
• Correctly handle EXTERNAL_MODULE_DIRS with docker makefiles/docker.inc.mk: Use directories in RIOT when possible #9646
• External CPU/BOARD
  • Makefile.include: introduce 'BOARDSDIR' for boards directory Makefile.include: introduce 'BOARDSDIR' for boards directory #12183
  • Makefile.include: fix board/cpu inconsistent include order Makefile.include: fix board/cpu inconsistent include order #8717
  • Process dependencies before BOARD/Makefile.include TODO
    • Build dependencies - processing order issues Build dependencies - processing order issues #9913
    • Fix board/cpu defining dependencies in Makefile.include TODO
  • makefiles/arch/cortexm.inc.mk uses RIOTCPU to get the common directory so cannot be reused

In the same time with the same idea, I try to also make packages self contained

• pseudomodules: allow defining them in pkg/PKG/Makefile.include pseudomodules: allow defining them in pkg/PKG/Makefile.include #9003
• WIP RFC Replace usage of USEPKG by USEMODULE. WIP RFC Replace usage of USEPKG by USEMODULE. #9307
• Move packages tests to package directory TODO (ref tests: split unittests?)
  • packages tests moved outside of unittests: tests/unittests: Move large unittests to individual tests tests/unittests: Move large unittests to individual tests #10187

[jia200x]

awesome feature

Are you considering to include different sources? (e.g fetching a module from a github repo, from the file system or from a URL should be transparent to the builder). This way makes possible to have alternative implementation of modules that might live in a different repo

[cladmi]

That was proposed by kaspaar: #8987 (comment)

There are still things to solve before but could be yes.

[maribu]

Support for external modules is mature these days and part of the regular CI checks.