manual: adding-package-directory.txt: update, cleanup and typo fixes

source "package/libfoo/Config.in"

--------------------------

[[depends-on-vs-select]]

The +Config.in+ file of your package must also ensure that

dependencies are enabled. Typically, Buildroot uses the following

rules:

  dependencies are selected. For example, the _libgtk2_ package uses

  +select BR2_PACKAGE_LIBGLIB2+ to make sure this library is also

  enabled.

  The +select+ keyword express the dependency with a backward

  semantic.

* Use a +depends on+ type of dependency when the user really needs to

  be aware of the dependency. Typically, Buildroot uses this type of

  dependency for dependencies on toolchain options (large file

  support, RPC support, IPV6 support), or for dependencies on "big"

  things, such as the X.org system. In some cases, especially

  dependency on toolchain options, it is recommended to add a

  +comment+ displayed when the option is not enabled, so that the user

  knows why the package is not available.

  dependency for dependencies on toolchain options (target

  architecture, MMU support, C library, C++ support, large file

  support, thread support, RPC support, IPV6 support, WCHAR support),

  or for dependencies on "big" things, such as the X.org system. In

  some cases, especially dependency on toolchain options, it is

  recommended to add a +comment+ displayed when the option is not

  enabled, so that the user knows why the package is not available.

  The +depends on+ keyword express the dependency with a forward

  semantic.

.Note

The current problem with the _kconfig_ language is that these two

dependency semantics are not internally linked. Therefore, it may be

possible to select a package, whom one of its dependencies/requirement

is not met.

An example illustrates both the usage of +select+ and +depends on+.

so, the dependency also needs to be expressed in the +.mk+ file of the

package.

Further formating details: see xref:writing-rules-config-in[the

writing rules].

The +.mk+ file

^^^^^^^^^^^^^^

   CMake. We cover them through a xref:cmake-package-tutorial[tutorial]

   and xref:cmake-package-reference[reference].

* *Hand-written Makefiles:* These are currently obsolete, and no new

  manual Makefiles should be added. However, since there are still

  many of them in the tree, we keep them documented in a

  xref:handwritten-tutorial[tutorial].

Further formating details: see xref:writing-rules-mk[the writing

rules].