* Documented the standard environment, including the generic builder.
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Eelco Dolstra
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@ -1285,7 +1285,256 @@ character, or inline/multi-line, enclosed within <literal>/*
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<sect1 id='sec-standard-environment'><title>The standard environment</title>
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<sect1 id='sec-standard-environment'><title>The standard environment</title>
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<para>TODO</para>
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<para>The standard build environment in the Nix Packages collection
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provides a basic environment for building Unix packages. It consists
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of the following components:
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<itemizedlist>
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<listitem><para>The GNU C Compiler, configured with C and C++
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support. On Linux, the compiler has been patched to provide greater
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<quote>purity</quote> assurance. For instance, the compiler doesn't
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search in locations such as <filename>/usr/include</filename>. In
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fact, attempts to add such directories through the
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<option>-I</option> flag are filtered out. Likewise, the linker
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(from GNU binutils) doesn't search in standard locations such as
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<filename>/usr/lib</filename>. Programs built on Linux are linked
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against a GNU C Library that likewise doesn't search in the default
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system locations.</para></listitem>
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<listitem><para>GNU coreutils (contains a few dozen standard Unix
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commands).</para></listitem>
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<listitem><para>GNU findutils (contains
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<command>find</command>).</para></listitem>
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<listitem><para>GNU diffutils (contains <command>diff</command>,
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<command>cmp</command>).</para></listitem>
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<listitem><para>GNU <command>sed</command>.</para></listitem>
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<listitem><para>GNU <command>grep</command>.</para></listitem>
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<listitem><para>GNU <command>awk</command>.</para></listitem>
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<listitem><para>GNU <command>tar</command>.</para></listitem>
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<listitem><para><command>gzip</command> and
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<command>bzip2</command>.</para></listitem>
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<listitem><para>GNU Make. It has been patched to provide
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<quote>nested</quote> output that can be fed into the
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<command>log2xml</command> command and <command>log2html</command>
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stylesheet to create a structured, readable output of the build
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steps performed by Make.</para></listitem>
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<listitem><para>Bash. This is the shell used for all builders in
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the Nix Packages collection. Not using <command>/bin/sh</command>
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removes a large source of portability problems.</para></listitem>
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<listitem><para>Patch.</para></listitem>
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</itemizedlist>
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</para>
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<para>The standard environment is used by passing it as an input
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called <envar>stdenv</envar> to the derivation, and then doing
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<programlisting>
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. $stdenv/setup</programlisting>
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at the top of the builder.</para>
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<para>Apart from adding the aforementioned commands to the
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<envar>PATH</envar>, <filename>setup</filename> also does the
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following:
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<itemizedlist>
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<listitem><para>All input components specified in the
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<envar>buildInputs</envar> environment variable have their
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<filename>/bin</filename> subdirectory added to <envar>PATH</envar>,
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their <filename>/include</filename> subdirectory added to the C/C++
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header file search path, and their <filename>/lib</filename>
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subdirectory added to the linker search path. This can be extended.
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For instance, when the <command>pkgconfig</command> component is
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used, the subdirectory <filename>/lib/pkgconfig</filename> of each
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input is added to the <envar>PKG_CONFIG_PATH</envar> environment
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variable.</para></listitem>
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<listitem><para>The environment variable
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<envar>NIX_CFLAGS_STRIP</envar> is set so that the compiler strips
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debug information from object files. This can be disabled by
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setting <envar>NIX_STRIP_DEBUG</envar> to
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<literal>0</literal>.</para></listitem>
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</itemizedlist>
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</para>
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<para>The <filename>setup</filename> script also exports a function
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called <function>genericBuilder</function> that knows how to build
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typical Autoconf-style components. It can be customised to perform
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builds for any type of component. It is advisable to use
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<function>genericBuild</function> since it provides facilities that
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are almost always useful such as unpacking of sources, patching of
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sources, nested logging, etc.</para>
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<para>The operation of the generic builder can be modified in many
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places by setting certain variables. These <emphasis>hook
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variables</emphasis> are typically set to the name of some shell
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function defined by you. For instance, to perform some additional
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steps after <command>make install</command> you would set the
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<varname>postInstall</varname> variable:
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<programlisting>
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postInstall=myPostInstall
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myPostInstall() {
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mkdir $out/share/extra
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cp extrafiles/* $out/share/extra
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}</programlisting>
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</para>
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<para>The generic builder has a number of <emphasis>phases</emphasis>,
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each of which can be override in its entirety by setting the indicated
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variable. The phases are:
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<itemizedlist>
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<listitem>
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<para><function>unpackPhase</function>: unpacks the source files
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listed in the <envar>src</envar> environment variable to the
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current directory. It supports <filename>tar</filename> files,
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optionally compressed with <command>gzip</command> or
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<command>bzip2</command>; Zip files (but note that the
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<command>unzip</command> command is not a part of the standard
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environment; you should add it as a build input yourself); and
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unpacked source trees (i.e., directories; they are copied
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verbatim). You can add support for other file types by setting
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the <varname>findUnpacker</varname> hook. This hook should set an
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the variable <varname>unpackCmd</varname> to contain the command
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to be executed to unpack the file.</para>
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<para>After unpacking all source files,
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<function>unpackPhase</function> changes the current directory to
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the directory created by unpacking the sources. If there are
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multiple source directories, you should set
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<varname>sourceRoot</varname> to the name of the intended
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directory.</para>
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<para>It also calls the hook <varname>postUnpack</varname> after
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unpacking.</para>
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</listitem>
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<listitem><para><function>patchPhase</function> calls the
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<command>patch</command> command with the <option>-p1</option>
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option for each patch file listed in the <envar>patches</envar>
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variable.</para></listitem>
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<listitem>
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<para><function>configurePhase</function> runs the script called
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<filename>configure</filename> in the current directory with a
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<option>--prefix</option> set to the output path. You can add
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additional flag through the <varname>configureFlags</varname>
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variable. If <filename>configure</filename> does not exist,
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nothing happens.</para>
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<para>Before and after running <filename>configure</filename>, the
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hooks <varname>preConfigure</varname> and
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<varname>postConfigure</varname> are called, respectively.</para>
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</listitem>
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<listitem>
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<para><function>buildPhase</function> calls
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<command>make</command>. You can set flags for
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<command>make</command> through the <varname>makeFlags</varname>
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variable.</para>
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<para>Before and after running <command>make</command>, the hooks
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<varname>preBuild</varname> and <varname>postBuild</varname> are
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called, respectively.</para>
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</listitem>
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<listitem><para><function>checkPhase</function> calls <command>make
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check</command>, but only if the <varname>doCheck</varname> variable
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is set to <literal>1</literal>. Additional flags can be set through
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the <varname>checkFlags</varname> variable.</para></listitem>
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<listitem>
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<para><function>installPhase</function> calls <command>make
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install</command>. Additional flags can be set through the
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<varname>installFlags</varname> variable. It also strips any
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static libraries in the output path of debug information unless
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<varname>dontStrip</varname> is set to
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<literal>1</literal>.</para>
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<para>Before and after running <command>make install</command>,
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the hooks <varname>preInstall</varname> and
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<varname>postInstall</varname> are called, respectively.</para>
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</listitem>
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<listitem>
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<para><function>distPhase</function> calls <command>make
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dist</command>, but only if the <varname>doDist</varname> variable
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is set to <literal>1</literal>. Additional flags can be set
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through the <varname>distFlags</varname> variable. The resulting
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tarball is copied to the <filename>/tarballs</filename>
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subdirectory of the output path.</para>
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<para>Before and after running <command>make dist</command>, the
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hooks <varname>preDist</varname> and <varname>postDist</varname>
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are called, respectively.</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>You can change the order in which phases are executed, or add
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new phases, by setting the <varname>phases</varname> variable. The
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default is <literal>patchPhase configurePhase buildPhase checkPhase
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installPhase distPhase</literal>.</para>
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<para>At the beginning of each phase, the set of all shell variables
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is written to the file <filename>env-vars</filename> at the top-level
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build directory. This is useful for debugging: it allows you to
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recreate the environment in which a build was performed. For
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instance, if a build fails, then assuming you used the
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<option>-K</option> flag, you can go to the output directory and
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<quote>switch</quote> to the environment of the builder:
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<screen>
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$ nix-build -K ./foo.nix
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... fails, keeping build directory `/tmp/nix-1234-0'
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$ cd /tmp/nix-1234-0
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$ source env-vars
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<lineannotation>(edit some files...)</lineannotation>
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$ make
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<lineannotation>(execution continues with the same GCC, make, etc.)</lineannotation></screen>
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</para>
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<para>The definitive, up-to-date documentation of the generic builder
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is the source itself, which resides in
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<filename>pkgs/stdenv/generic/setup.sh</filename>.</para>
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</sect1>
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</sect1>
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