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stdenv.xml
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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-stdenv">
<title>The Standard Environment</title>
<para>
The standard build environment in the Nix Packages collection provides an
environment for building Unix packages that does a lot of common build tasks
automatically. In fact, for Unix packages that use the standard
<literal>./configure; make; make install</literal> build interface, you
don’t need to write a build script at all; the standard environment does
everything automatically. If <literal>stdenv</literal> doesn’t do what you
need automatically, you can easily customise or override the various build
phases.
</para>
<section xml:id="sec-using-stdenv">
<title>Using <literal>stdenv</literal></title>
<para>
To build a package with the standard environment, you use the function
<varname>stdenv.mkDerivation</varname>, instead of the primitive built-in
function <varname>derivation</varname>, e.g.
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
src = fetchurl {
url = http://example.org/libfoo-1.2.3.tar.bz2;
sha256 = "0x2g1jqygyr5wiwg4ma1nd7w4ydpy82z9gkcv8vh2v8dn3y58v5m";
};
}</programlisting>
(<varname>stdenv</varname> needs to be in scope, so if you write this in a
separate Nix expression from <filename>pkgs/all-packages.nix</filename>, you
need to pass it as a function argument.) Specifying a
<varname>name</varname> and a <varname>src</varname> is the absolute minimum
you need to do. Many packages have dependencies that are not provided in the
standard environment. It’s usually sufficient to specify those
dependencies in the <varname>buildInputs</varname> attribute:
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
buildInputs = [libbar perl ncurses];
}</programlisting>
This attribute ensures that the <filename>bin</filename> subdirectories of
these packages appear in the <envar>PATH</envar> environment variable during
the build, that their <filename>include</filename> subdirectories are
searched by the C compiler, and so on. (See
<xref linkend="ssec-setup-hooks"/> for details.)
</para>
<para>
Often it is necessary to override or modify some aspect of the build. To
make this easier, the standard environment breaks the package build into a
number of <emphasis>phases</emphasis>, all of which can be overridden or
modified individually: unpacking the sources, applying patches, configuring,
building, and installing. (There are some others; see
<xref linkend="sec-stdenv-phases"/>.) For instance, a package that doesn’t
supply a makefile but instead has to be compiled “manually” could be
handled like this:
<programlisting>
stdenv.mkDerivation {
name = "fnord-4.5";
...
buildPhase = ''
gcc foo.c -o foo
'';
installPhase = ''
mkdir -p $out/bin
cp foo $out/bin
'';
}</programlisting>
(Note the use of <literal>''</literal>-style string literals, which are very
convenient for large multi-line script fragments because they don’t need
escaping of <literal>"</literal> and <literal>\</literal>, and because
indentation is intelligently removed.)
</para>
<para>
There are many other attributes to customise the build. These are listed in
<xref linkend="ssec-stdenv-attributes"/>.
</para>
<para>
While the standard environment provides a generic builder, you can still
supply your own build script:
<programlisting>
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
builder = ./builder.sh;
}</programlisting>
where the builder can do anything it wants, but typically starts with
<programlisting>
source $stdenv/setup
</programlisting>
to let <literal>stdenv</literal> set up the environment (e.g., process the
<varname>buildInputs</varname>). If you want, you can still use
<literal>stdenv</literal>’s generic builder:
<programlisting>
source $stdenv/setup
buildPhase() {
echo "... this is my custom build phase ..."
gcc foo.c -o foo
}
installPhase() {
mkdir -p $out/bin
cp foo $out/bin
}
genericBuild
</programlisting>
</para>
</section>
<section xml:id="sec-tools-of-stdenv">
<title>Tools provided by <literal>stdenv</literal></title>
<para>
The standard environment provides the following packages:
<itemizedlist>
<listitem>
<para>
The GNU C Compiler, configured with C and C++ support.
</para>
</listitem>
<listitem>
<para>
GNU coreutils (contains a few dozen standard Unix commands).
</para>
</listitem>
<listitem>
<para>
GNU findutils (contains <command>find</command>).
</para>
</listitem>
<listitem>
<para>
GNU diffutils (contains <command>diff</command>, <command>cmp</command>).
</para>
</listitem>
<listitem>
<para>
GNU <command>sed</command>.
</para>
</listitem>
<listitem>
<para>
GNU <command>grep</command>.
</para>
</listitem>
<listitem>
<para>
GNU <command>awk</command>.
</para>
</listitem>
<listitem>
<para>
GNU <command>tar</command>.
</para>
</listitem>
<listitem>
<para>
<command>gzip</command>, <command>bzip2</command> and
<command>xz</command>.
</para>
</listitem>
<listitem>
<para>
GNU Make. It has been patched to provide <quote>nested</quote> output
that can be fed into the <command>nix-log2xml</command> command and
<command>log2html</command> stylesheet to create a structured, readable
output of the build steps performed by Make.
</para>
</listitem>
<listitem>
<para>
Bash. This is the shell used for all builders in the Nix Packages
collection. Not using <command>/bin/sh</command> removes a large source
of portability problems.
</para>
</listitem>
<listitem>
<para>
The <command>patch</command> command.
</para>
</listitem>
</itemizedlist>
</para>
<para>
On Linux, <literal>stdenv</literal> also includes the
<command>patchelf</command> utility.
</para>
</section>
<section xml:id="ssec-stdenv-dependencies">
<title>Specifying dependencies</title>
<para>
As described in the Nix manual, almost any <filename>*.drv</filename> store
path in a derivation's attribute set will induce a dependency on that
derivation. <varname>mkDerivation</varname>, however, takes a few attributes
intended to, between them, include all the dependencies of a package. This
is done both for structure and consistency, but also so that certain other
setup can take place. For example, certain dependencies need their bin
directories added to the <envar>PATH</envar>. That is built-in, but other
setup is done via a pluggable mechanism that works in conjunction with these
dependency attributes. See <xref linkend="ssec-setup-hooks"/> for details.
</para>
<para>
Dependencies can be broken down along three axes: their host and target
platforms relative to the new derivation's, and whether they are propagated.
The platform distinctions are motivated by cross compilation; see
<xref linkend="chap-cross"/> for exactly what each platform means.
<footnote xml:id="footnote-stdenv-ignored-build-platform">
<para>
The build platform is ignored because it is a mere implementation detail
of the package satisfying the dependency: As a general programming
principle, dependencies are always <emphasis>specified</emphasis> as
interfaces, not concrete implementation.
</para>
</footnote>
But even if one is not cross compiling, the platforms imply whether or not
the dependency is needed at run-time or build-time, a concept that makes
perfect sense outside of cross compilation. For now, the run-time/build-time
distinction is just a hint for mental clarity, but in the future it perhaps
could be enforced.
</para>
<para>
The extension of <envar>PATH</envar> with dependencies, alluded to
above, proceeds according to the relative platforms alone. The
process is carried out only for dependencies whose host platform
matches the new derivation's build platform i.e. dependencies which
run on the platform where the new derivation will be built.
<footnote xml:id="footnote-stdenv-native-dependencies-in-path">
<para>
Currently, this means for native builds all dependencies are put
on the <envar>PATH</envar>. But in the future that may not be the
case for sake of matching cross: the platforms would be assumed
to be unique for native and cross builds alike, so only the
<varname>depsBuild*</varname> and
<varname>nativeBuildInputs</varname> would be added to the
<envar>PATH</envar>.
</para>
</footnote>
For each dependency <replaceable>dep</replaceable> of those dependencies,
<filename><replaceable>dep</replaceable>/bin</filename>, if present, is
added to the <envar>PATH</envar> environment variable.
</para>
<para>
The dependency is propagated when it forces some of its other-transitive
(non-immediate) downstream dependencies to also take it on as an immediate
dependency. Nix itself already takes a package's transitive dependencies into
account, but this propagation ensures nixpkgs-specific infrastructure like
setup hooks (mentioned above) also are run as if the propagated dependency.
</para>
<para>
It is important to note that dependencies are not necessarily propagated as
the same sort of dependency that they were before, but rather as the
corresponding sort so that the platform rules still line up. The exact rules
for dependency propagation can be given by assigning to each dependency two
integers based one how its host and target platforms are offset from the
depending derivation's platforms. Those offsets are given below in the
descriptions of each dependency list attribute. Algorithmically, we traverse
propagated inputs, accumulating every propagated dependency's propagated
dependencies and adjusting them to account for the "shift in perspective"
described by the current dependency's platform offsets. This results in sort
a transitive closure of the dependency relation, with the offsets being
approximately summed when two dependency links are combined. We also prune
transitive dependencies whose combined offsets go out-of-bounds, which can be
viewed as a filter over that transitive closure removing dependencies that
are blatantly absurd.
</para>
<para>
We can define the process precisely with
<link xlink:href="https://en.wikipedia.org/wiki/Natural_deduction">Natural
Deduction</link> using the inference rules. This probably seems a bit
obtuse, but so is the bash code that actually implements it!
<footnote xml:id="footnote-stdenv-find-inputs-location">
<para>
The <function>findInputs</function> function, currently residing in
<filename>pkgs/stdenv/generic/setup.sh</filename>, implements the
propagation logic.
</para>
</footnote>
They're confusing in very different ways so... hopefully if something doesn't
make sense in one presentation, it will in the other!
<programlisting>
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
propagated-dep(h0, t0, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, 1}
-------------------------------------- Transitive property
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)</programlisting>
<programlisting>
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
dep(h0, _, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, -1}
----------------------------- Take immediate dependencies' propagated dependencies
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)</programlisting>
<programlisting>
propagated-dep(h, t, A, B)
----------------------------- Propagated dependencies count as dependencies
dep(h, t, A, B)</programlisting>
Some explanation of this monstrosity is in order. In the common case, the
target offset of a dependency is the successor to the target offset:
<literal>t = h + 1</literal>. That means that:
<programlisting>
let f(h, t, i) = i + (if i <= 0 then h else t - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else (h + 1) - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else h)
let f(h, h + 1, i) = i + h
</programlisting>
This is where "sum-like" comes in from above: We can just sum all of the host
offsets to get the host offset of the transitive dependency. The target
offset is the transitive dependency is simply the host offset + 1, just as it
was with the dependencies composed to make this transitive one; it can be
ignored as it doesn't add any new information.
</para>
<para>
Because of the bounds checks, the uncommon cases are <literal>h = t</literal>
and <literal>h + 2 = t</literal>. In the former case, the motivation for
<function>mapOffset</function> is that since its host and target platforms
are the same, no transitive dependency of it should be able to "discover" an
offset greater than its reduced target offsets.
<function>mapOffset</function> effectively "squashes" all its transitive
dependencies' offsets so that none will ever be greater than the target
offset of the original <literal>h = t</literal> package. In the other case,
<literal>h + 1</literal> is skipped over between the host and target offsets.
Instead of squashing the offsets, we need to "rip" them apart so no
transitive dependencies' offset is that one.
</para>
<para>
Overall, the unifying theme here is that propagation shouldn't be introducing
transitive dependencies involving platforms the depending package is unaware
of. The offset bounds checking and definition of
<function>mapOffset</function> together ensure that this is the case.
Discovering a new offset is discovering a new platform, and since those
platforms weren't in the derivation "spec" of the needing package, they
cannot be relevant. From a capability perspective, we can imagine that the
host and target platforms of a package are the capabilities a package
requires, and the depending package must provide the capability to the
dependency.
</para>
<variablelist>
<title>Variables specifying dependencies</title>
<varlistentry>
<term>
<varname>depsBuildBuild</varname>
</term>
<listitem>
<para>
A list of dependencies whose host and target platforms are the new
derivation's build platform. This means a <literal>-1</literal> host and
<literal>-1</literal> target offset from the new derivation's platforms.
These are programs and libraries used at build time that produce programs
and libraries also used at build time. If the dependency doesn't care
about the target platform (i.e. isn't a compiler or similar tool), put it
in <varname>nativeBuildInputs</varname> instead. The most common use of
this <literal>buildPackages.stdenv.cc</literal>, the default C compiler
for this role. That example crops up more than one might think in old
commonly used C libraries.
</para>
<para>
Since these packages are able to be run at build-time, they are always
added to the <envar>PATH</envar>, as described above. But since these
packages are only guaranteed to be able to run then, they shouldn't
persist as run-time dependencies. This isn't currently enforced, but could
be in the future.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>nativeBuildInputs</varname>
</term>
<listitem>
<para>
A list of dependencies whose host platform is the new derivation's build
platform, and target platform is the new derivation's host platform. This
means a <literal>-1</literal> host offset and <literal>0</literal> target
offset from the new derivation's platforms. These are programs and
libraries used at build-time that, if they are a compiler or similar tool,
produce code to run at run-time—i.e. tools used to build the new
derivation. If the dependency doesn't care about the target platform (i.e.
isn't a compiler or similar tool), put it here, rather than in
<varname>depsBuildBuild</varname> or <varname>depsBuildTarget</varname>.
This could be called <varname>depsBuildHost</varname> but
<varname>nativeBuildInputs</varname> is used for historical continuity.
</para>
<para>
Since these packages are able to be run at build-time, they are added to
the <envar>PATH</envar>, as described above. But since these packages are
only guaranteed to be able to run then, they shouldn't persist as run-time
dependencies. This isn't currently enforced, but could be in the future.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsBuildTarget</varname>
</term>
<listitem>
<para>
A list of dependencies whose host platform is the new derivation's build
platform, and target platform is the new derivation's target platform.
This means a <literal>-1</literal> host offset and <literal>1</literal>
target offset from the new derivation's platforms. These are programs used
at build time that produce code to run with code produced by the depending
package. Most commonly, these are tools used to build the runtime or
standard library that the currently-being-built compiler will inject into
any code it compiles. In many cases, the currently-being-built-compiler is
itself employed for that task, but when that compiler won't run (i.e. its
build and host platform differ) this is not possible. Other times, the
compiler relies on some other tool, like binutils, that is always built
separately so that the dependency is unconditional.
</para>
<para>
This is a somewhat confusing concept to wrap one’s head around, and for
good reason. As the only dependency type where the platform offsets are
not adjacent integers, it requires thinking of a bootstrapping stage
<emphasis>two</emphasis> away from the current one. It and its use-case go
hand in hand and are both considered poor form: try to not need this sort
of dependency, and try to avoid building standard libraries and runtimes
in the same derivation as the compiler produces code using them. Instead
strive to build those like a normal library, using the newly-built
compiler just as a normal library would. In short, do not use this
attribute unless you are packaging a compiler and are sure it is needed.
</para>
<para>
Since these packages are able to run at build time, they are added to the
<envar>PATH</envar>, as described above. But since these packages are only
guaranteed to be able to run then, they shouldn't persist as run-time
dependencies. This isn't currently enforced, but could be in the future.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsHostHost</varname>
</term>
<listitem>
<para>
A list of dependencies whose host and target platforms match the new
derivation's host platform. This means a <literal>0</literal> host offset
and <literal>0</literal> target offset from the new derivation's host
platform. These are packages used at run-time to generate code also used
at run-time. In practice, this would usually be tools used by compilers
for macros or a metaprogramming system, or libraries used by the macros or
metaprogramming code itself. It's always preferable to use a
<varname>depsBuildBuild</varname> dependency in the derivation being built
over a <varname>depsHostHost</varname> on the tool doing the building for
this purpose.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>buildInputs</varname>
</term>
<listitem>
<para>
A list of dependencies whose host platform and target platform match the
new derivation's. This means a <literal>0</literal> host offset and a
<literal>1</literal> target offset from the new derivation's host
platform. This would be called <varname>depsHostTarget</varname> but for
historical continuity. If the dependency doesn't care about the target
platform (i.e. isn't a compiler or similar tool), put it here, rather than
in <varname>depsBuildBuild</varname>.
</para>
<para>
These are often programs and libraries used by the new derivation at
<emphasis>run</emphasis>-time, but that isn't always the case. For
example, the machine code in a statically-linked library is only used at
run-time, but the derivation containing the library is only needed at
build-time. Even in the dynamic case, the library may also be needed at
build-time to appease the linker.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsTargetTarget</varname>
</term>
<listitem>
<para>
A list of dependencies whose host platform matches the new derivation's
target platform. This means a <literal>1</literal> offset from the new
derivation's platforms. These are packages that run on the target
platform, e.g. the standard library or run-time deps of standard library
that a compiler insists on knowing about. It's poor form in almost all
cases for a package to depend on another from a future stage [future
stage corresponding to positive offset]. Do not use this attribute unless
you are packaging a compiler and are sure it is needed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsBuildBuildPropagated</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>depsBuildBuild</varname>. This
perhaps never ought to be used, but it is included for consistency [see
below for the others].
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>propagatedNativeBuildInputs</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>nativeBuildInputs</varname>. This
would be called <varname>depsBuildHostPropagated</varname> but for
historical continuity. For example, if package <varname>Y</varname> has
<literal>propagatedNativeBuildInputs = [X]</literal>, and package
<varname>Z</varname> has <literal>buildInputs = [Y]</literal>, then
package <varname>Z</varname> will be built as if it included package
<varname>X</varname> in its <varname>nativeBuildInputs</varname>. If
instead, package <varname>Z</varname> has <literal>nativeBuildInputs =
[Y]</literal>, then <varname>Z</varname> will be built as if it included
<varname>X</varname> in the <varname>depsBuildBuild</varname> of package
<varname>Z</varname>, because of the sum of the two <literal>-1</literal>
host offsets.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsBuildTargetPropagated</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>depsBuildTarget</varname>. This is
prefixed for the same reason of alerting potential users.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsHostHostPropagated</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>depsHostHost</varname>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>propagatedBuildInputs</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>buildInputs</varname>. This would
be called <varname>depsHostTargetPropagated</varname> but for historical
continuity.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>depsTargetTargetPropagated</varname>
</term>
<listitem>
<para>
The propagated equivalent of <varname>depsTargetTarget</varname>. This is
prefixed for the same reason of alerting potential users.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-stdenv-attributes">
<title>Attributes</title>
<variablelist>
<title>Variables affecting <literal>stdenv</literal> initialisation</title>
<varlistentry>
<term>
<varname>NIX_DEBUG</varname>
</term>
<listitem>
<para>
A natural number indicating how much information to log. If set to 1 or
higher, <literal>stdenv</literal> will print moderate debugging
information during the build. In particular, the <command>gcc</command>
and <command>ld</command> wrapper scripts will print out the complete
command line passed to the wrapped tools. If set to 6 or higher, the
<literal>stdenv</literal> setup script will be run with <literal>set
-x</literal> tracing. If set to 7 or higher, the <command>gcc</command>
and <command>ld</command> wrapper scripts will also be run with
<literal>set -x</literal> tracing.
</para>
</listitem>
</varlistentry>
</variablelist>
<variablelist>
<title>Attributes affecting build properties</title>
<varlistentry>
<term>
<varname>enableParallelBuilding</varname>
</term>
<listitem>
<para>
If set to <literal>true</literal>, <literal>stdenv</literal> will pass
specific flags to <literal>make</literal> and other build tools to enable
parallel building with up to <literal>build-cores</literal> workers.
</para>
<para>
Unless set to <literal>false</literal>, some build systems with good
support for parallel building including <literal>cmake</literal>,
<literal>meson</literal>, and <literal>qmake</literal> will set it to
<literal>true</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
<variablelist>
<title>Special variables</title>
<varlistentry>
<term>
<varname>passthru</varname>
</term>
<listitem>
<para>
This is an attribute set which can be filled with arbitrary values. For
example:
<programlisting>
passthru = {
foo = "bar";
baz = {
value1 = 4;
value2 = 5;
};
}
</programlisting>
</para>
<para>
Values inside it are not passed to the builder, so you can change them
without triggering a rebuild. However, they can be accessed outside of a
derivation directly, as if they were set inside a derivation itself, e.g.
<literal>hello.baz.value1</literal>. We don't specify any usage or schema
of <literal>passthru</literal> - it is meant for values that would be
useful outside the derivation in other parts of a Nix expression (e.g. in
other derivations). An example would be to convey some specific dependency
of your derivation which contains a program with plugins support. Later,
others who make derivations with plugins can use passed-through dependency
to ensure that their plugin would be binary-compatible with built program.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="sec-stdenv-phases">
<title>Phases</title>
<para>
The generic builder has a number of <emphasis>phases</emphasis>. Package
builds are split into phases to make it easier to override specific parts of
the build (e.g., unpacking the sources or installing the binaries).
Furthermore, it allows a nicer presentation of build logs in the Nix build
farm.
</para>
<para>
Each phase can be overridden in its entirety either by setting the
environment variable <varname><replaceable>name</replaceable>Phase</varname>
to a string containing some shell commands to be executed, or by redefining
the shell function <varname><replaceable>name</replaceable>Phase</varname>.
The former is convenient to override a phase from the derivation, while the
latter is convenient from a build script. However, typically one only wants
to <emphasis>add</emphasis> some commands to a phase, e.g. by defining
<literal>postInstall</literal> or <literal>preFixup</literal>, as skipping
some of the default actions may have unexpected consequences.
</para>
<section xml:id="ssec-controlling-phases">
<title>Controlling phases</title>
<para>
There are a number of variables that control what phases are executed and
in what order:
<variablelist>
<title>Variables affecting phase control</title>
<varlistentry>
<term>
<varname>phases</varname>
</term>
<listitem>
<para>
Specifies the phases. You can change the order in which phases are
executed, or add new phases, by setting this variable. If it’s not
set, the default value is used, which is <literal>$prePhases
unpackPhase patchPhase $preConfigurePhases configurePhase
$preBuildPhases buildPhase checkPhase $preInstallPhases installPhase
fixupPhase $preDistPhases distPhase $postPhases</literal>.
</para>
<para>
Usually, if you just want to add a few phases, it’s more convenient
to set one of the variables below (such as
<varname>preInstallPhases</varname>), as you then don’t specify all
the normal phases.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>prePhases</varname>
</term>
<listitem>
<para>
Additional phases executed before any of the default phases.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preConfigurePhases</varname>
</term>
<listitem>
<para>
Additional phases executed just before the configure phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preBuildPhases</varname>
</term>
<listitem>
<para>
Additional phases executed just before the build phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preInstallPhases</varname>
</term>
<listitem>
<para>
Additional phases executed just before the install phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preFixupPhases</varname>
</term>
<listitem>
<para>
Additional phases executed just before the fixup phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preDistPhases</varname>
</term>
<listitem>
<para>
Additional phases executed just before the distribution phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>postPhases</varname>
</term>
<listitem>
<para>
Additional phases executed after any of the default phases.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</section>
<section xml:id="ssec-unpack-phase">
<title>The unpack phase</title>
<para>
The unpack phase is responsible for unpacking the source code of the
package. The default implementation of <function>unpackPhase</function>
unpacks the source files listed in the <envar>src</envar> environment
variable to the current directory. It supports the following files by
default:
<variablelist>
<varlistentry>
<term>
Tar files
</term>
<listitem>
<para>
These can optionally be compressed using <command>gzip</command>
(<filename>.tar.gz</filename>, <filename>.tgz</filename> or
<filename>.tar.Z</filename>), <command>bzip2</command>
(<filename>.tar.bz2</filename>, <filename>.tbz2</filename> or
<filename>.tbz</filename>) or <command>xz</command>
(<filename>.tar.xz</filename>, <filename>.tar.lzma</filename> or
<filename>.txz</filename>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Zip files
</term>
<listitem>
<para>
Zip files are unpacked using <command>unzip</command>. However,
<command>unzip</command> is not in the standard environment, so you
should add it to <varname>nativeBuildInputs</varname> yourself.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Directories in the Nix store
</term>
<listitem>
<para>
These are simply copied to the current directory. The hash part of the
file name is stripped, e.g.
<filename>/nix/store/1wydxgby13cz...-my-sources</filename> would be
copied to <filename>my-sources</filename>.
</para>
</listitem>
</varlistentry>
</variablelist>
Additional file types can be supported by setting the
<varname>unpackCmd</varname> variable (see below).
</para>
<para></para>
<variablelist>
<title>Variables controlling the unpack phase</title>
<varlistentry>
<term>
<varname>srcs</varname> / <varname>src</varname>
</term>
<listitem>
<para>
The list of source files or directories to be unpacked or copied. One of
these must be set.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>sourceRoot</varname>
</term>
<listitem>
<para>
After running <function>unpackPhase</function>, the generic builder
changes the current directory to the directory created by unpacking the
sources. If there are multiple source directories, you should set
<varname>sourceRoot</varname> to the name of the intended directory.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>setSourceRoot</varname>
</term>
<listitem>
<para>
Alternatively to setting <varname>sourceRoot</varname>, you can set
<varname>setSourceRoot</varname> to a shell command to be evaluated by
the unpack phase after the sources have been unpacked. This command must
set <varname>sourceRoot</varname>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>preUnpack</varname>
</term>
<listitem>
<para>
Hook executed at the start of the unpack phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>postUnpack</varname>
</term>
<listitem>
<para>
Hook executed at the end of the unpack phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>dontMakeSourcesWritable</varname>
</term>
<listitem>
<para>
If set to <literal>1</literal>, the unpacked sources are
<emphasis>not</emphasis> made writable. By default, they are made
writable to prevent problems with read-only sources. For example, copied
store directories would be read-only without this.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>unpackCmd</varname>
</term>
<listitem>
<para>
The unpack phase evaluates the string <literal>$unpackCmd</literal> for
any unrecognised file. The path to the current source file is contained
in the <varname>curSrc</varname> variable.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="ssec-patch-phase">
<title>The patch phase</title>
<para>
The patch phase applies the list of patches defined in the
<varname>patches</varname> variable.
</para>
<variablelist>
<title>Variables controlling the patch phase</title>
<varlistentry>
<term>
<varname>patches</varname>
</term>
<listitem>
<para>
The list of patches. They must be in the format accepted by the
<command>patch</command> command, and may optionally be compressed using
<command>gzip</command> (<filename>.gz</filename>),
<command>bzip2</command> (<filename>.bz2</filename>) or
<command>xz</command> (<filename>.xz</filename>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>patchFlags</varname>
</term>
<listitem>
<para>
Flags to be passed to <command>patch</command>. If not set, the argument
<option>-p1</option> is used, which causes the leading directory
component to be stripped from the file names in each patch.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>prePatch</varname>
</term>
<listitem>
<para>
Hook executed at the start of the patch phase.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>postPatch</varname>
</term>
<listitem>
<para>
Hook executed at the end of the patch phase.
</para>