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|
<?xml version="1.0" encoding="UTF-8"?>
<guide self="general-concepts/dependencies/">
<chapter>
<title>Dependencies</title>
<body>
<p>
Automatic dependency resolution is one of the most useful features
provided by <c>emerge</c>.
</p>
<p>
You are encouraged to sort dependencies alphabetically, with unconditional
dependencies grouped together, then all conditional dependencies. There is an
exception: you may sort dependencies as per upstream listings if it eases
checking for changes. Some projects may have different policies <d/> consult
them if you're not sure.
</p>
<p>
Please also see the following section on
<uri link="::general-concepts/ebuild-revisions/"/>
for how dependencies and revisions interact.
</p>
</body>
<section>
<title>Dependency types</title>
<subsection>
<title>CHOST vs CBUILD</title>
<body>
<p>
In order to avoid ambiguity, we use the following terms to indicate different
systems when cross-compiling. They serve as a shorthand for an overall system
in addition to their literal value (e.g. $CHOST).
</p>
<dl>
<dt>CBUILD</dt>
<dd>
The system on which the build is performed. Dependencies that apply
to the CBUILD system can be executed during build time.
</dd>
<dt>CHOST</dt>
<dd>
The system on which the package is going to be executed. When
cross-compiling, dependencies applying to CHOST can not be executed.
</dd>
</dl>
<p>
When cross-compiling, CBUILD and CHOST are naturally different, as are the
actual install paths for the different types of dependencies.
</p>
<p>
Note however that, while cross-compiling is used to help explain these concepts,
it is not strictly required. CBUILD and CHOST could target the exact same
hardware, but be installed into distinct SYSROOT/ROOT paths. The dependency
distinctions still apply even if it isn't, strictly speaking, cross-compiling.
</p>
</body>
</subsection>
<subsection>
<title>Build dependencies</title>
<body>
<p>
Build dependencies are used to specify any dependencies that are required
to unpack, patch, compile, test or install the package (but see
<uri link="::general-concepts/dependencies/#Implicit system dependency"/> for
exemptions).
</p>
<p>
Starting with EAPI 7, build dependencies are split into two variables:
<c>BDEPEND</c> and <c>DEPEND</c>. <c>BDEPEND</c> specifies dependencies
applicable to CBUILD, i.e. programs that need to be executed during the build,
e.g. <c>virtual/pkgconfig</c>. <c>DEPEND</c> specifies dependencies for CHOST,
i.e. packages that need to be found on built system, e.g. libraries and headers.
</p>
<p>
In earlier EAPIs, all build dependencies are placed in <c>DEPEND</c>.
</p>
</body>
</subsection>
<subsection>
<title>Runtime dependencies</title>
<body>
<p>
The <c>RDEPEND</c> ebuild variable should specify any dependencies which are
required at runtime. This includes libraries (when dynamically linked), any data
packages and (for interpreted languages) the relevant interpreter.
</p>
<p>
Note that when installing from a binary package, only <c>RDEPEND</c> will be
checked. It is therefore necessary to include items even if they are also listed
in <c>DEPEND</c>.
</p>
<p>
Items which are in <c>RDEPEND</c> but not <c>DEPEND</c> could <e>in theory</e> be merged
<e>after</e> the target package. Portage does not currently do this.
</p>
</body>
</subsection>
<subsection>
<title>Post dependencies</title>
<body>
<p>
The <c>PDEPEND</c> variable specifies runtime dependencies that do not strictly
require being satisfied immediately. They can be merged <e>after</e>
the package. This variable is used purely to resolve circular dependencies,
while in general case <c>RDEPEND</c> should be used instead.
</p>
</body>
</subsection>
</section>
<section>
<title>Dependency syntax</title>
<subsection>
<title>Basic dependency syntax</title>
<body>
<p>
A basic <c>DEPEND</c> specification might look like the following:
</p>
<codesample lang="ebuild">
DEPEND="dev-lang/ruby
dev-ruby/ruby-gtk2
dev-ruby/mysql-ruby"
</codesample>
<p>
Each <e>package dependency specification</e> is the full category and name of
a package. Dependency specifications are separated by arbitrary whitespace <d/>
convention is to have one specification per line for readability purposes.
When specifying names, the category part should be treated as mandatory.
</p>
</body>
</subsection>
<subsection>
<title>Version dependencies</title>
<body>
<p>
Sometimes a particular version of a package is needed. Where this is known, it
should be specified. A simple example:
</p>
<codesample lang="ebuild">
DEPEND=">=dev-libs/openssl-0.9.7d"
</codesample>
<p>
This states that at least version 0.9.7d of <c>openssl</c> is required.
</p>
</body>
<subsubsection>
<title>Version specifiers</title>
<body>
<p>
Available version specifiers are:
</p>
<table>
<tr>
<th>Specifier</th>
<th>Meaning</th>
</tr>
<tr>
<ti><c>>=app-misc/foo-1.23</c></ti>
<ti>Version 1.23 or later is required.</ti>
</tr>
<tr>
<ti><c>>app-misc/foo-1.23</c></ti>
<ti>A version strictly later than 1.23 is required.</ti>
</tr>
<tr>
<ti><c>~app-misc/foo-1.23</c></ti>
<ti>Version 1.23 (or any <c>1.23-r*</c>) is required.</ti>
</tr>
<tr>
<ti><c>=app-misc/foo-1.23</c></ti>
<ti>
Exactly version 1.23 is required. If at all possible,
use the <c>~</c> form to simplify revision bumps.
</ti>
</tr>
<tr>
<ti><c><=app-misc/foo-1.23</c></ti>
<ti>Version 1.23 or older is required.</ti>
</tr>
<tr>
<ti><c><app-misc/foo-1.23</c></ti>
<ti>A version strictly before 1.23 is required.</ti>
</tr>
</table>
</body>
</subsubsection>
<subsubsection>
<title>Ranged dependencies</title>
<body>
<p>
To specify "version 2.x (not 1.x or 3.x)" of a package, it is necessary to use
the asterisk postfix. This is most commonly seen in situations like:
</p>
<codesample lang="ebuild">
DEPEND="gtk? ( =x11-libs/gtk+-2* )"
</codesample>
<p>
Note that the equals sign is mandatory, and that there is no dot before the
asterisk. Also note that when selecting all versions in a specific
<c>SLOT</c>, <c>SLOT</c> dependencies should be used (see below).
</p>
</body>
</subsubsection>
<subsubsection>
<title>Blockers</title>
<body>
<p>
When two packages (package slots, versions) can not be installed
simultaneously, blockers can be used to expose such a conflict
to the package manager.
</p>
<p>
There are two kinds of blockers: <e>weak blockers</e> and <e>strong
blockers</e>.
</p>
<p>
A weak blocker is defined using the following syntax:
</p>
<codesample lang="ebuild">
RDEPEND="!app-misc/foo"
</codesample>
<p>
The package manager will try to resolve this conflict automatically.
The package blocked by a weak blocker can be uninstalled <e>after</e>
installing the package blocking it. However, it exempts the common
files from file collision checks. Weak blockers are usually used
to solve file collisions between packages and are meaningful only
in <c>RDEPEND</c>.
</p>
<p>
More specifically, installation of the newer package may overwrite any
colliding files that belong to the older package that is explicitly blocked.
When such file collisions occur, the colliding files cease to belong to the
older package, and they remain installed after the older package is eventually
uninstalled. The older package is uninstalled only after any newer blocking
packages have been merged on top of it.
</p>
<warning>
Weak blockers that are pure <c>DEPEND</c> <e>do not work correctly</e>.
While Portage seemingly queues the package for removal, it <e>does not</e>
exempt their contents from file collision checks. Always include your
weak blockers in <c>RDEPEND</c>!
</warning>
<p>
If it is strictly necessary to resolve the blocker before the package
is built (installed), a strong blocker must be used instead. In this case,
temporary simultaneous installation of the conflicting packages is not allowed.
Strong blockers are expressed using the following syntax:
</p>
<codesample lang="ebuild">
RDEPEND="!!app-misc/foo"
</codesample>
<p>
Strong blockers apply accordingly to the dependency type defining them.
Blockers defined in <c>RDEPEND</c> are enforced as long as the package
is installed (but do not prevent building binary packages). Blockers
defined purely in <c>DEPEND</c> are enforced only for building
the package from source, and may not apply once the package is installed
or when it is installed from a binary package.
</p>
<p>
The most common use for strong blockers is where another package simply
being installed causes a build failure. Strong blockers are not to be used
to prevent just file collisions.
</p>
<note>
If both weak and strong blockers match a given package, the strong blocker
takes precedence.
</note>
<p>
Specific versions can also be blocked:
</p>
<codesample lang="ebuild">
RDEPEND="!<app-misc/foo-1.3"
</codesample>
<p>
Blockers can be optional based upon <c>USE</c> flags as per normal
dependencies.
</p>
<p>
Blockers added to older ebuilds should not be expected to be retroactive. If
the user already has the ebuild installed, any changes to the ebuild should not
be expected to make any difference. This means that you should add the
blockers to whichever ebuild is the newest (even if it means that logically it
would seem backwards). For example, certain versions of Portage don't like
some versions of bash, but the blocker was put into bash because that was the
newer package that caused the issues.
</p>
</body>
</subsubsection>
</subsection>
<subsection>
<title>SLOT dependencies</title>
<body>
<p>
To depend on a specific <c>SLOT</c>, <c>:SLOT</c> should be appended to
the package name, where 'SLOT' is the <c>SLOT</c> of the package wanted:
</p>
<codesample lang="ebuild">
DEPEND="qt5? ( dev-qt/qtcore:5 )
gtk? ( x11-libs/gtk+:2 )
</codesample>
<p>
To depend on a specific version or version-range within a SLOT we use:
</p>
<codesample lang="ebuild">
DEPEND="qt5? ( ~dev-qt/qtcore-5.15.2:5 )
gtk? ( >=x11-libs/gtk+-2.24.9:2 )
</codesample>
</body>
<subsubsection>
<title>Slot operators</title>
<body>
<p>
In <c>EAPI=5</c> and higher, you can use slot operators appended to the package
name to declare whether or not your package should be rebuilt after the versions
satisfying its runtime dependencies are updated to versions with a different slot
or <uri link="::general-concepts/slotting/#Sub-slots">sub-slot</uri>:
</p>
<ul>
<li>
<c>:=</c> means that any slot is acceptable. Additionally indicates that
your package should be rebuilt if the version best matching the runtime
dependency is updated to a version with a different slot or subslot.
</li>
<li>
<c>:*</c> means that any slot is acceptable. Furthermore, this slot
operator explicitly declares that changes in the slot or sub-slot can be
ignored.
</li>
<li>
<c>:SLOT=</c> means that only the 'SLOT' slot is acceptable. It otherwise
behaves identically to the <c>:=</c> operator. That is, the package must be
rebuilt if the sub-slot of the dependency changes.
</li>
<li>
<c>:SLOT</c> means that only the 'SLOT' slot is acceptable, and that changes
in the sub-slot can be ignored (like in previous EAPIs).
</li>
<li>
<c>:SLOT/SUBSLOT</c> means a dependency on a specific slot and sub-slot pair,
which can be useful for packages installing pre-built binaries that require a
library with a particular soname version corresponding to the sub-slot.
</li>
</ul>
<p>
For example:
</p>
<codesample lang="ebuild">
RDEPEND="media-libs/cogl:1.0=
gnutls? ( >=net-libs/gnutls-2.8:= )"
</codesample>
<p>
means that only the '1.0' slot is acceptable for <c>media-libs/cogl</c> and
that sub-slot changes of <c>media-libs/cogl</c> will cause a rebuild of the
dependent package. It furthermore means that every slot of
<c>net-libs/gnutls</c> is acceptable but any slot change is causing a rebuild.
</p>
<p>
The <c>:slot</c> dependency syntax continues to behave like in <c>EAPI=4</c> or
earlier, i.e. it indicates that only the specific slot value is acceptable and
that the package will not break when the currently installed version of the
dependency is replaced by a version with a different sub-slot.
</p>
<p>
For example:
</p>
<codesample lang="ebuild">
RDEPEND="dev-libs/foo:2=
>=dev-libs/bar-0.9:=
media-gfx/baz:*
x11-misc/wombat:0"
</codesample>
<p>
means that the package should be rebuilt when <c>foo:2</c> or
<c>>=bar-0.9</c> are upgraded to versions with different subslots. On the
other hand, changes in slot or sub-slots of <c>baz</c> should be ignored, and
sub-slot changes of <c>wombat:0</c> should be ignored.
</p>
</body>
</subsubsection>
</subsection>
<subsection>
<title>USE-conditional dependencies</title>
<body>
<p>
To depend upon a certain package only if a given <c>USE</c> flag is set:
</p>
<codesample lang="ebuild">
DEPEND="perl? ( dev-lang/perl )
ruby? ( >=dev-lang/ruby-1.8 )
python? ( dev-lang/python )"
</codesample>
<p>
It is also possible to depend upon a certain package if a given <c>USE</c> flag is
<e>not</e> set:
</p>
<codesample lang="ebuild">
RDEPEND="!crypt? ( net-misc/netkit-rsh )"
</codesample>
<p>
This should <b>not</b> be used for disabling a certain <c>USE</c> flag on a given
architecture. In order to do this, the architecture team should add the <c>USE</c>
flag to their <c>use.mask</c> file in the <c>profiles/arch</c>
directory of the Gentoo repository.
</p>
<p>
This can be nested:
</p>
<codesample lang="ebuild">
DEPEND="!build? (
>=sys-libs/ncurses-5.2-r2
gcj? (
>=media-libs/libart_lgpl-2.1
gtk? (
x11-libs/libXt
x11-libs/libX11
x11-libs/libXtst
x11-proto/xproto
x11-proto/xextproto
>=x11-libs/gtk+-2.2
x11-libs/pango
)
)
nls? ( sys-devel/gettext )
)"
</codesample>
</body>
</subsection>
<subsection>
<title>Any of many dependencies</title>
<body>
<note>
To ease dependency resolution for Portage, it is recommended that you sort
the elements in <e>preferred</e> order first. See
<uri link="https://bugs.gentoo.org/489458">this bug</uri> for more context.
</note>
<p>
To depend on either <c>foo</c> or <c>bar</c>:
</p>
<codesample lang="ebuild">
DEPEND="|| ( app-misc/foo app-misc/bar )"
</codesample>
<p>
To depend on either <c>foo</c> or <c>bar</c> if the <c>baz</c> <c>USE</c> flag is set:
</p>
<codesample lang="ebuild">
DEPEND="baz? ( || ( app-misc/foo app-misc/bar ) )"
</codesample>
</body>
<subsubsection>
<title>Any of many versus USE</title>
<body>
<p>
Say <c>fnord</c> can be built against either <c>foo</c> or <c>bar</c>. Then a <c>USE</c>
flag is not necessary if and only if all of the following hold:
</p>
<ul>
<li>
<c>fnord</c> is merged on a system which has <c>foo</c> and not <c>bar</c> installed.
<c>foo</c> is then unmerged, and <c>bar</c> is installed. <c>fnord</c> must continue to
work correctly.
</li>
<li>
A binary package of <c>fnord</c> made on a system with <c>foo</c> and not <c>bar</c>
can be taken and installed on a system with <c>bar</c> and not <c>foo</c>.
</li>
</ul>
</body>
</subsubsection>
</subsection>
<subsection>
<title>Built with USE dependencies</title>
<body>
<p>
Available specifiers are:
</p>
<table>
<tr>
<th>Specifier</th>
<th>Meaning</th>
</tr>
<tr>
<ti><c>app-misc/foo[bar]</c></ti>
<ti>foo must have bar enabled.</ti>
</tr>
<tr>
<ti><c>app-misc/foo[bar,baz]</c></ti>
<ti>foo must have both bar and baz enabled.</ti>
</tr>
<tr>
<ti><c>app-misc/foo[-bar,baz]</c></ti>
<ti>foo must have bar disabled and baz enabled.</ti>
</tr>
</table>
<p>
There are also shortcuts for conditional situations:
</p>
<table>
<tr>
<th>Compact form</th>
<th>Equivalent expanded form</th>
</tr>
<tr>
<ti><c>app-misc/foo[bar?]</c></ti>
<ti><c>bar? ( app-misc/foo[bar] ) !bar? ( app-misc/foo )</c></ti>
</tr>
<tr>
<ti><c>app-misc/foo[!bar?]</c></ti>
<ti><c>bar? ( app-misc/foo ) !bar? ( app-misc/foo[-bar] )</c></ti>
</tr>
<tr>
<ti><c>app-misc/foo[bar=]</c></ti>
<ti><c>bar? ( app-misc/foo[bar] ) !bar? ( app-misc/foo[-bar] )</c></ti>
</tr>
<tr>
<ti><c>app-misc/foo[!bar=]</c></ti>
<ti><c>bar? ( app-misc/foo[-bar] ) !bar? ( app-misc/foo[bar] )</c></ti>
</tr>
</table>
</body>
<subsubsection>
<title>Use dependency defaults</title>
<body>
<p>
If a dependency is introducing or removing a <c>USE</c> flag in a new package
version, a <c>(+)</c> or <c>(-)</c> may be added to the use-dependency
specification to define a default value in case the flag does not exist in the
target package. The <c>(+)</c> indicates that the missing flag is assumed to be
enabled, <c>(-)</c> the opposite.
</p>
<p>
For example, the following will treat all <c>boost</c> versions without the
<c>threads</c> flag as having it enabled, and all <c>gcc</c> versions without
the <c>openmp</c> as having it disabled:
</p>
<codesample lang="ebuild">
DEPEND="
>=dev-libs/boost-1.48[threads(+)]
sys-devel/gcc[openmp(-)]"
</codesample>
</body>
</subsubsection>
</subsection>
</section>
<section>
<title>Tips for checking dependencies</title>
<body>
<p>
It is important to ensure that all the dependencies are complete for your
package:
</p>
<dl>
<dt>Look at installed binaries/libraries</dt>
<dd>
Use a tool like <c>scanelf -n</c> (from app-misc/pax-utils) or
<c>objdump -p</c> (from sys-devel/binutils) to list <c>DT_NEEDED</c>
entries.
app-portage/iwdevtools and portage's own <c>qa-unresolved-soname-deps</c>
<b>FEATURE</b> can help finding these.
</dd>
<dt>Look in <c>configure.ac</c></dt>
<dd>
Look for checks for packages in here. Things to look out for are pkg-config
checks or <c>AM_*</c> functions that check for a specific version.
</dd>
<dt>Look at included <c>.spec</c> files</dt>
<dd>
A good indication of dependencies is to look at the included <c>.spec</c>
files for relevant deps. However, do not trust them to be the definitive
complete list of dependencies.
</dd>
<dt>Look at the application/library website</dt>
<dd>
Check the application website for possible dependencies that they suggest
are needed.
</dd>
<dt>Read the <c>README</c> and <c>INSTALL</c> for the package</dt>
<dd>
They usually also contain useful information about building and installing
packages.
</dd>
<dt>
Remember non-binary dependencies such as pkg-config, doc generation
programs, etc. Such programs would usually belong in <c>BDEPEND</c>.
</dt>
<dd>
Usually the build process requires some dependencies such as intltool,
libtool, pkg-config, doxygen, scrollkeeper, gtk-doc, etc. Make sure those
are clearly stated. Again, such dependencies usually belong in
<c>BDEPEND</c>.
</dd>
<dt>Testing in chroots, containers and virtual machines</dt>
<dd>
A sure-way to find missing dependencies is to test your ebuild in a
deprived environment. Chroots, containers, virtual machines and
<c>dev-util/ebuildtester</c> can achieve this.
</dd>
</dl>
</body>
</section>
<section>
<title>Implicit system dependency</title>
<body>
<p>
All packages have an implicit compile-time and runtime dependency upon the
entire <c>@system</c> set. It is therefore not necessary, nor advisable, to
specify dependencies upon toolchain packages like <c>gcc</c>, <c>libc</c> and
so on, except where specific versions or packages (for example, <c>glibc</c>
over <c>uclibc</c>) are required. Note that this rule also needs consideration
for packages like <c>flex</c>, <c>zlib</c> and <c>libtool</c>, which aren't in
the <c>@system</c> set for every profile. For example, the embedded profile
doesn't have <c>zlib</c> in <c>@system</c>, the <c>libtool</c> ABI might
change and break building order and <c>flex</c> might get removed from the
<c>@system</c> set in future.
</p>
<p>
However, packages which are included in the <c>@system</c> set, or are
dependencies of <c>@system</c> set packages, should generally include
a complete dependency list (excluding bootstrap packages). This makes
<c>emerge -e @system</c> possible when installing from a stage 1 or stage 2
tarball.
</p>
</body>
</section>
<section>
<title>Test dependencies</title>
<body>
<p>
Packages often have optional dependencies that are needed only when running
tests. These should be specified in DEPEND behind a USE flag. Often, the
'test' USE flag is used for this purpose.
</p>
<p>
Since testing will likely fail when test dependencies are not installed, the
test phase should be disabled in this case. This may be accomplished via USE
conditionals in the RESTRICT variable.
</p>
<p>
If other optional features must be enabled/disabled when testing, REQUIRED_USE
may be set to express this.
</p>
<codesample lang="ebuild">
# Define some USE flags
IUSE="debug test"
# Require debug support when tests are enabled
REQUIRED_USE="test? ( debug )"
# Disable test phase when test USE flag is disabled
RESTRICT="!test? ( test )"
# Running tests requires 'foo' to be installed
DEPEND="test? ( dev-util/foo )"
</codesample>
</body>
</section>
<section>
<title>Circular dependencies</title>
<body>
<p>
Circular dependencies occur if one or more of package's (possibly indirect)
dependencies depend on the package itself. This creates a dependency cycle where
each of the packages must technically be installed before the other.
For example, if package A depends on B, B depends on C and C depends on A, then
the package manager cannot install A before C, and C before A.
</p>
<p>
There are three kinds of circular dependencies:
</p>
<ol>
<li>
Circular dependencies that occur if only one of the packages strictly needs
to be installed before the other. For example, <c>dev-python/certifi</c>
strictly requires <c>dev-python/setuptools</c> to build but the latter
package requires the former for some runtime functionality. As a result,
<c>dev-python/certifi</c> can be installed later than the other package.
<c>PDEPEND</c> is used to express this and automatically resolve
the circular dependency.
</li>
<li>
Circular dependencies that occur if the cycle applies only to some
combination of USE flags on one of the packages. For example, running tests
in <c>dev-python/setuptools</c> requires a number of packages which require
<c>dev-python/setuptools</c> to be installed first. This kind of circular
dependency can be resolved by the user by adjusting USE flags on one
of the packages, e.g. by disabling tests on <c>dev-python/setuptools</c>,
and reenabling them once the dependency is initially installed.
</li>
<li>
Circular dependencies that cannot be resolved using the regular means.
For example, <c>dev-util/cmake</c> used to depend
on <c>dev-libs/jsoncpp</c>, while the latter package used the former
to build. Resolving this kind of dependency usually requires bundling one
of the dependencies conditionally, or providing an alternate bootstrap path.
</li>
</ol>
</body>
</section>
<section>
<title>Indirect dependencies</title>
<body>
<p>
Always list each direct dependency that your package needs to build and run
correctly. Do not rely on dependency chains to meet the dependency
requirements. For example, a package needs <c>dep1</c> and <c>dep2</c>, but
<c>dep1</c> also depends on <c>dep2</c>. You might consider just adding
<c>dep1</c> since it currently pulls <c>dep2</c> too, but in the future,
<c>dep1</c> might drop <c>dep2</c> as a dependency, or make it conditional with
USE flags. This would then break building your ebuild.
</p>
</body>
</section>
</chapter>
</guide>
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