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* Manual updates (especially how nix-build makes testing packages much

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easier; no longer need a helper expression).
This commit is contained in:
Eelco Dolstra 2006-10-02 11:50:55 +00:00
parent 91a01e6fcf
commit f316b6c1a9
5 changed files with 120 additions and 81 deletions
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118
doc/manual/writing-nix-expressions.xml
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@ -35,7 +35,7 @@ need to do three things:
the inputs.</para></listitem>
<listitem><para>Add the component to the file
<filename>pkgs/system/all-packages-generic.nix</filename>. The Nix
<filename>pkgs/top-level/all-packages.nix</filename>. The Nix
expression written in the first step is a
<emphasis>function</emphasis>; it requires other components in order
to build it. In this step you put it all together, i.e., you call
@ -309,7 +309,7 @@ error check.</para>
<section><title>Composition</title>
<example xml:id='ex-hello-composition'><title>Composing GNU Hello
(<filename>all-packages-generic.nix</filename>)</title>
(<filename>all-packages.nix</filename>)</title>
<programlisting>
...
@ -336,11 +336,11 @@ rec { <co xml:id='ex-hello-composition-co-1' />
<para>The Nix expression in <xref linkend='ex-hello-nix' /> is a
function; it is missing some arguments that have to be filled in
somewhere. In the Nix Packages collection this is done in the file
<filename>pkgs/system/all-packages-generic.nix</filename>, where all
<filename>pkgs/top-level/all-packages.nix</filename>, where all
Nix expressions for components are imported and called with the
appropriate arguments. <xref linkend='ex-hello-composition' /> shows
some fragments of
<filename>all-packages-generic.nix</filename>.</para>
<filename>all-packages.nix</filename>.</para>
<calloutlist>
@ -361,7 +361,7 @@ some fragments of
GNU Hello. The import operation just loads and returns the
specified Nix expression. In fact, we could just have put the
contents of <xref linkend='ex-hello-nix' /> in
<filename>all-packages-generic.nix</filename> at this point. That
<filename>all-packages.nix</filename> at this point. That
would be completely equivalent, but it would make the file rather
bulky.</para>
@ -406,71 +406,38 @@ some fragments of
<section><title>Testing</title>
<para>You can now try to build Hello. The simplest way to do that is
by using <command>nix-env</command>:
<para>You can now try to build Hello. Of course, you could do
<literal>nix-env -f pkgs/top-level/all-packages.nix -i hello</literal>,
but you may not want to install a possibly broken package just yet.
The best way to test the package is by using the command <command
linkend="sec-nix-build">nix-build</command>, which builds a Nix
expression and creates a symlink named <filename>result</filename> in
the current directory:
<screen>
$ nix-env -f pkgs/system/i686-linux.nix -i hello
installing `hello-2.1.1'
building path `/nix/store/632d2b22514dcebe704887c3da15448d-hello-2.1.1'
$ nix-build pkgs/top-level/all-packages.nix -A hello
building path `/nix/store/632d2b22514d...-hello-2.1.1'
hello-2.1.1/
hello-2.1.1/intl/
hello-2.1.1/intl/ChangeLog
<replaceable>...</replaceable>
</screen>
This will build Hello and install it into your profile. The file
<filename>i686-linux</filename> is just a simple Nix expression that
imports <filename>all-packages-generic.nix</filename> and instantiates
it for Linux on the x86 platform.</para>
$ ls -l result
lrwxrwxrwx ... 2006-09-29 10:43 result -> /nix/store/632d2b22514d...-hello-2.1.1
<para>Note that the <literal>hello</literal> argument here refers to
the symbolic name given to the Hello derivation (the
<varname>name</varname> attribute in <xref linkend='ex-hello-nix' />),
<emphasis>not</emphasis> the <varname>hello</varname> attribute in
<filename>all-packages-generic.nix</filename>.
<command>nix-env</command> simply walks through all derivations
defined in the latter file, looking for one with a
<varname>name</varname> attribute matching the command-line
argument.</para>
<para>You can test whether it works:
<screen>
$ hello
Hello, world!</screen>
</para>
<para>Generally, however, using <command>nix-env</command> is not the
best way to test components, since you may not want to install them
into your profile right away (they might not work properly, after
all). A better way is to write a short file containing the
following:
<programlisting>
(import pkgs/system/i686-linux.nix).hello</programlisting>
Call it <filename>test.nix</filename>. You can then build it without
installing it using the command <link
linkend="sec-nix-build"><command>nix-build</command></link>:
<screen>
$ nix-build ./test.nix
...
/nix/store/632d2b22514dcebe704887c3da15448d-hello-2.1.1</screen>
<command>nix-build</command> will build the derivation and print the
output path. It also creates a symlink to the output path called
<filename>result</filename> in the current directory. This is
convenient for testing the component:
<screen>
$ ./result/bin/hello
Hello, world!</screen>
</para>
<para><command>nix-build</command> registers the
<filename>./result</filename> symlink as a garbage collection root, so
unless and until you delete the <filename>./result</filename> symlink,
the output of the build will be safely kept on your system. You can
use <command>nix-build</command>’s <option
linkend='opt-out-link'>-o</option> switch to give the symlink another
name.</para>
<para>Nix has a transactional semantics. Once a build finishes
successfully, Nix makes a note of this in its database: it registers
that the path denoted by <envar>out</envar> is now
@ -492,14 +459,22 @@ error due to a syntax error in the source) and transient failures
simultaneously, and they try to build the same derivation, the first
Nix instance that gets there will perform the build, while the others
block (or perform other derivations if available) until the build
finishes. So it is always safe to run multiple instances of Nix in
parallel (contrary to, say, <command>make</command>).</para>
finishes:
<screen>
$ nix-build pkgs/top-level/all-packages.nix -A hello
waiting for lock on `/nix/store/0h5b7hp8d4hqfrw8igvx97x1xawrjnac-hello-2.1.1x'</screen>
So it is always safe to run multiple instances of Nix in parallel
(which isn’t the case with, say, <command>make</command>).</para>
<para>If you have a system with multiple CPUs, you may want to have
Nix build different derivations in parallel (insofar as possible).
Just pass the option <option>-j <replaceable>N</replaceable></option>,
where <replaceable>N</replaceable> is the maximum number of jobs to be
run in parallel. Typically this should be the number of CPUs.</para>
Just pass the option <option linkend='opt-max-jobs'>-j
<replaceable>N</replaceable></option>, where
<replaceable>N</replaceable> is the maximum number of jobs to be run
in parallel, or set. Typically this should be the number of
CPUs.</para>
</section>
@ -794,7 +769,7 @@ evaluates to <literal>{x = 123; y = 456;}</literal>. (Note that this
works because <varname>x</varname> is added to the lexical scope by
the <literal>let</literal> construct.) It is also possible to inherit
attributes from another attribute set. For instance, in this fragment
from <filename>all-packages-generic.nix</filename>,
from <filename>all-packages.nix</filename>,
<programlisting>
graphviz = (import ../tools/graphics/graphviz) {
@ -1392,6 +1367,13 @@ builds for any type of component. It is advisable to use
are almost always useful such as unpacking of sources, patching of
sources, nested logging, etc.</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>
<section><title>Customising the generic builder</title>
<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
@ -1519,6 +1501,11 @@ new phases, by setting the <varname>phases</varname> variable. The
default is <literal>patchPhase configurePhase buildPhase checkPhase
installPhase distPhase</literal>.</para>
</section>
<section><title>Debugging failed builds</title>
<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
@ -1543,9 +1530,8 @@ $ make
</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>
</section>
</section>