Previously, external modules had to be individually added to both
EXTERNAL_MODULE_DIRS and USEMODULE. If those where not in sync, this
resulted in build errors.
With this commit, search folders for external modules are added to
EXTERNAL_MODULE_DIRS instead. So lets say the file system structure is
like this
```
└── /path/to/external/modules
├── mod_a
│ ├── Makefile
│ ├── Makefile.dep
│ ├── Makefile.include
│ ├── foo.c
│ └── include
│ └── external_module.h
└── mod_b
├── Makefile
└── bar.c
```
One now adds `/path/to/external/modules` to EXTERNAL_MODULES and only
with `USEMODULE += mod_a` the corresponding module, dependencies and
include settings are actually used. Hence, it is possible to configure
`EXTERNAL_MODULE_DIRS` from `~/.profile` or `~/.bashrc` once and never
needs to worry about them again.
Goals:
- Untangle dependency resolution and feature checking for better maintainability
- Improve performance of "make info-boards-supported"
Changes:
- Makefile.dep
- Dropped handling of default modules and recursion
- Now only dependencies of the current set of used modules and pkgs are
added
==> External recursion is needed to catch transient dependencies
- Changed Makefile.features:
- Dropped checking of provided features
- Dropped populating FEATURES_USED with provided features that are required
or optional
- Dropped populating FEATURES_MISSING with required but not provided
features
- Dropped adding modules implementing used features to USE_MODULE
==> This now only populates FEATURES_PROVIDED, nothing more
- Added makefiles/features_check.inc.mk:
- This performs the population of FEATURES_USED and FEATURES_MISSING now
- Added makefiles/features_modules.inc.mk:
- This performs now the addition of modules implementing used features
- Added makefiles/dependency_resolution.inc.mk:
- This now performs the recursion required to catch transient dependencies
- Also the feature check is performed recursively to handle also required
and optional features of the transient dependencies
- DEFAULT_MODULES are added repeatedly to allow it to be extended based on
used features and modules
==> This allows modules to have optional dependencies, as these
dependencies can be blacklisted
- Use simply expanded variables instead of recursively expended variables
(`foo := $(bar)` instead `foo = $(bar)`) for internal variables during feature
resolution. This improves performance significantly for
`make info-boards-supported`.
- Reduce dependency resolution steps in `make info-boards-supported`
- Globally resolve dependencies without any features (including arch)
provided
==> This results in the common subset of feature requirements and modules
used
- But for individual boards additional modules might be used on top due
to architecture specific dependencies or optional features
- Boards not supporting this subset of commonly required features are not
supported, so no additional dependency resolution is needed for them
- For each board supporting the common set of requirements a complete
dependency resolution is still needed to also catch architecture specific
hacks
- But this resolution is seeded with the common set of dependencies to
speed this up
