* Documented the standard environment, including the generic builder.

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Eelco Dolstra 2004-11-07 22:12:16 +00:00
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@ -1285,7 +1285,256 @@ character, or inline/multi-line, enclosed within <literal>/*
<sect1 id='sec-standard-environment'><title>The standard environment</title>
<para>TODO</para>
<para>The standard build environment in the Nix Packages collection
provides a basic environment for building Unix packages. It consists
of the following components:
<itemizedlist>
<listitem><para>The GNU C Compiler, configured with C and C++
support. On Linux, the compiler has been patched to provide greater
<quote>purity</quote> assurance. For instance, the compiler doesn't
search in locations such as <filename>/usr/include</filename>. In
fact, attempts to add such directories through the
<option>-I</option> flag are filtered out. Likewise, the linker
(from GNU binutils) doesn't search in standard locations such as
<filename>/usr/lib</filename>. Programs built on Linux are linked
against a GNU C Library that likewise doesn't search in the default
system locations.</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> and
<command>bzip2</command>.</para></listitem>
<listitem><para>GNU Make. It has been patched to provide
<quote>nested</quote> output that can be fed into the
<command>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>Patch.</para></listitem>
</itemizedlist>
</para>
<para>The standard environment is used by passing it as an input
called <envar>stdenv</envar> to the derivation, and then doing
<programlisting>
. $stdenv/setup</programlisting>
at the top of the builder.</para>
<para>Apart from adding the aforementioned commands to the
<envar>PATH</envar>, <filename>setup</filename> also does the
following:
<itemizedlist>
<listitem><para>All input components specified in the
<envar>buildInputs</envar> environment variable have their
<filename>/bin</filename> subdirectory added to <envar>PATH</envar>,
their <filename>/include</filename> subdirectory added to the C/C++
header file search path, and their <filename>/lib</filename>
subdirectory added to the linker search path. This can be extended.
For instance, when the <command>pkgconfig</command> component is
used, the subdirectory <filename>/lib/pkgconfig</filename> of each
input is added to the <envar>PKG_CONFIG_PATH</envar> environment
variable.</para></listitem>
<listitem><para>The environment variable
<envar>NIX_CFLAGS_STRIP</envar> is set so that the compiler strips
debug information from object files. This can be disabled by
setting <envar>NIX_STRIP_DEBUG</envar> to
<literal>0</literal>.</para></listitem>
</itemizedlist>
</para>
<para>The <filename>setup</filename> script also exports a function
called <function>genericBuilder</function> that knows how to build
typical Autoconf-style components. It can be customised to perform
builds for any type of component. It is advisable to use
<function>genericBuild</function> since it provides facilities that
are almost always useful such as unpacking of sources, patching of
sources, nested logging, etc.</para>
<para>The operation of the generic builder can be modified in many
places by setting certain variables. These <emphasis>hook
variables</emphasis> are typically set to the name of some shell
function defined by you. For instance, to perform some additional
steps after <command>make install</command> you would set the
<varname>postInstall</varname> variable:
<programlisting>
postInstall=myPostInstall
myPostInstall() {
mkdir $out/share/extra
cp extrafiles/* $out/share/extra
}</programlisting>
</para>
<para>The generic builder has a number of <emphasis>phases</emphasis>,
each of which can be override in its entirety by setting the indicated
variable. The phases are:
<itemizedlist>
<listitem>
<para><function>unpackPhase</function>: unpacks the source files
listed in the <envar>src</envar> environment variable to the
current directory. It supports <filename>tar</filename> files,
optionally compressed with <command>gzip</command> or
<command>bzip2</command>; Zip files (but note that the
<command>unzip</command> command is not a part of the standard
environment; you should add it as a build input yourself); and
unpacked source trees (i.e., directories; they are copied
verbatim). You can add support for other file types by setting
the <varname>findUnpacker</varname> hook. This hook should set an
the variable <varname>unpackCmd</varname> to contain the command
to be executed to unpack the file.</para>
<para>After unpacking all source files,
<function>unpackPhase</function> 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>
<para>It also calls the hook <varname>postUnpack</varname> after
unpacking.</para>
</listitem>
<listitem><para><function>patchPhase</function> calls the
<command>patch</command> command with the <option>-p1</option>
option for each patch file listed in the <envar>patches</envar>
variable.</para></listitem>
<listitem>
<para><function>configurePhase</function> runs the script called
<filename>configure</filename> in the current directory with a
<option>--prefix</option> set to the output path. You can add
additional flag through the <varname>configureFlags</varname>
variable. If <filename>configure</filename> does not exist,
nothing happens.</para>
<para>Before and after running <filename>configure</filename>, the
hooks <varname>preConfigure</varname> and
<varname>postConfigure</varname> are called, respectively.</para>
</listitem>
<listitem>
<para><function>buildPhase</function> calls
<command>make</command>. You can set flags for
<command>make</command> through the <varname>makeFlags</varname>
variable.</para>
<para>Before and after running <command>make</command>, the hooks
<varname>preBuild</varname> and <varname>postBuild</varname> are
called, respectively.</para>
</listitem>
<listitem><para><function>checkPhase</function> calls <command>make
check</command>, but only if the <varname>doCheck</varname> variable
is set to <literal>1</literal>. Additional flags can be set through
the <varname>checkFlags</varname> variable.</para></listitem>
<listitem>
<para><function>installPhase</function> calls <command>make
install</command>. Additional flags can be set through the
<varname>installFlags</varname> variable. It also strips any
static libraries in the output path of debug information unless
<varname>dontStrip</varname> is set to
<literal>1</literal>.</para>
<para>Before and after running <command>make install</command>,
the hooks <varname>preInstall</varname> and
<varname>postInstall</varname> are called, respectively.</para>
</listitem>
<listitem>
<para><function>distPhase</function> calls <command>make
dist</command>, but only if the <varname>doDist</varname> variable
is set to <literal>1</literal>. Additional flags can be set
through the <varname>distFlags</varname> variable. The resulting
tarball is copied to the <filename>/tarballs</filename>
subdirectory of the output path.</para>
<para>Before and after running <command>make dist</command>, the
hooks <varname>preDist</varname> and <varname>postDist</varname>
are called, respectively.</para>
</listitem>
</itemizedlist>
</para>
<para>You can change the order in which phases are executed, or add
new phases, by setting the <varname>phases</varname> variable. The
default is <literal>patchPhase configurePhase buildPhase checkPhase
installPhase distPhase</literal>.</para>
<para>At the beginning of each phase, the set of all shell variables
is written to the file <filename>env-vars</filename> at the top-level
build directory. This is useful for debugging: it allows you to
recreate the environment in which a build was performed. For
instance, if a build fails, then assuming you used the
<option>-K</option> flag, you can go to the output directory and
<quote>switch</quote> to the environment of the builder:
<screen>
$ nix-build -K ./foo.nix
... fails, keeping build directory `/tmp/nix-1234-0'
$ cd /tmp/nix-1234-0
$ source env-vars
<lineannotation>(edit some files...)</lineannotation>
$ make
<lineannotation>(execution continues with the same GCC, make, etc.)</lineannotation></screen>
</para>
<para>The definitive, up-to-date documentation of the generic builder
is the source itself, which resides in
<filename>pkgs/stdenv/generic/setup.sh</filename>.</para>
</sect1>