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Manual.md: revamp explain_depends section. 

Add useful examples of checkdepends that might not be obvious.
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Érico Rolim 2020-07-22 16:36:59 -03:00 committed by Michael Aldridge
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@ -727,36 +727,45 @@ Examples:
Do not use noarch. It is deprecated and being removed.
<a id="explain_depends"></a>
#### About the many types of `depends` variable.
#### About the many types of `depends` variables
So far we have listed four types of `depends`, there are `hostmakedepends`,
`makedepends`, `checkdepends` and plain old `depends`.To understand the difference
between them, understand this: Void Linux cross compiles for many arches.
Sometimes in a build process, certain programs must be run, for example `yacc`, or the
compiler itself for a C program. Those programs get put in `hostmakedepends`.
When the build runs, those will be installed on the host to help the build
complete.
So far, we have listed four types of `depends` variables: `hostmakedepends`,
`makedepends`, `checkdepends` and `depends`. These different kinds of variables
are necessary because `xbps-src` supports cross compilation and to avoid
installing unecessary packages in the build environment.
Then there are those things for which a package either links against or
includes header files. These are `makedepends`, and regardless of the
architecture of the build machine, the architecture of the target machine must
be used. Typically the `makedepends` will be the only one of the three types of
`depends` to include `-devel` packages, and typically only `-devel` packages.
During a build process, there are programs that must be _run_ on the host, such
as `yacc` or the C compiler. The packages that contain these programs should be
listed in `hostmakedepends`, and will be installed on the host when building the
target package. Some of these packages are dependencies of the `base-chroot`
package and don't need to be listed. It is possible that some of the programs
necessary to build a project are located in `-devel` packages.
Then there are those things that are required for a package to run its testsuite
`dejagnu` or libraries it must link to when building test binaries like `cmocka`.
These are `checkdepends` and they are installed like they are part of `makedepends`.
the difference is that they are only installed when `XBPS_CHECK_PKGS` is defined.
The target package can also depend on other packages for libraries to link
against or header files. These packages should be listed in `makedepends` and
will match the target architecture, regardless of the architecture of the build
machine. Typically, `makedepends` will contain mainly `-devel` packages.
The final variable, `depends`, is for those things the package needs at
runtime and without which is unusable, and that xbps can't auto-detect.
These are not all the packages the package needs at runtime, but only those
that are not linked against. This variable is most useful for non-compiled
programs.
Furthermore, if `XBPS_CHECK_PKGS` is set or the `-Q` option is passed to
`xbps-src`, the target package might require specific dependencies or libraries
that are linked into its test binaries to run its test suite. These dependencies
should be listed in `checkdepends` and will be installed as if they were part of
`hostmakedepends`. Some dependencies that can be included in `checkdepends` are:
Finally, as a general rule, if something compiles the exact same way whether or
not you add a particular package to `makedepends` or `hostmakedepends`, it
shouldn't be added.
- `dejagnu`: used for some GNU projects
- `cmocka-devel`: linked into test binaries
- `dbus`: makes it possible to run `dbus-run-session <test-command>` to provide
a D-Bus session for applications that need it
- `git`: some test suites run the `git` command
Lastly, a package may require certain dependencies at runtime, without which it
is unusable. These dependencies, when they aren't detected automatically by
XBPS, should be listed in `depends`. This is mostly relevant for Perl and Python
modules and other programs that use `dlopen(3)` instead of dynamically linking.
Finally, as a general rule, if a package is built the exact same way whether or
not a particular package is present in `makedepends` or `hostmakedepends`, that
package shouldn't be added as a build time dependency.
<a id="repositories"></a>
#### Repositories