doc: Write "Building from the Command Line".

[?]

Oct 12, 2011, 2:20 PM

EE53ECTSDLDTGK6RHSEZHZ42FKK2IIEMXQM5ZMDTQNFWZLR4RAIQC

Dependencies

[2] PKE6I67S doc: Import the "Creating Projects" chapter by Visser & Dolstra.
[3] 2LTNY56W doc: Add preliminary section about `release.nix'.

Change contents

replacement in doc/manual/projects.xml at line 356

[2.4946]→[2.4946:4994](∅→∅)

<title>Building on the Command Line</title>

[2.4946]

[2.4994]

<title>Building from the Command Line</title>

<para>
It is often useful to test a build recipe, for instance before
it is actually used by Hydra, when testing changes, or when
debugging a build issue. Since build recipes for Hydra jobsets
are just plain Nix expressions, they can be evaluated using the
standard Nix tools.
</para>

<para>
To evaluate the <varname>tarball</varname> jobset of <xref
linkend='ex-hello' />, just run:

<screen>
$ nix-build release.nix -A tarball
</screen>

However, doing this with <xref linkend='ex-hello' /> as is will
probably yield an error like this:

<screen>
error: cannot auto-call a function that has an argument without a default value (`nixpkgs')
</screen>

This is because no value was specified for the
<varname>nixpkgs</varname> argument of the Nix expression.
</para>

<para>
This is fixed by providing a default value for that argument in
the Nix expression, which will allow <command>nix-build</command>
to auto-call the function: instfead of writing <literal>{ nixpkgs
}:</literal>, we now write <literal>{ nixpkgs ? <nixpkgs>
}:</literal>. What it means is that, by default, the
<varname>nixpkgs</varname> variable will be bound to the absolute
path of any <filename>nixpkgs</filename> file found in the Nix
search path. Similarly, a default value for
<varname>helloSrc</varname> needs to be provided.
</para>
replacement in doc/manual/projects.xml at line 397

[2.4995]→[2.4995:5175](∅→∅)

Overigens zijn die helemaal niet Hydra-specifiek, je kunt ze gewoon vanaf de
command line bouwen, bijv. als je een patchelf checkout hebt (met een nixpkgs
checkout in ../nixpkgs):

[2.4995]

[2.5175]

<para>
Thus, assuming a checkout of Nixpkgs is available under
<filename>$HOME/src/nixpkgs</filename>, the
<varname>tarball</varname> jobset can now be evaluated by running:
replacement in doc/manual/projects.xml at line 402

[2.5176]→[2.5176:5239](∅→∅)

<screen>
$ nix-build release.nix -A rpm_fedora10i386
</screen>

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[2.5239]

<screen>
$ nix-build -I ~/src release.nix -A tarball
</screen>

Similarly, the <varname>build</varname> jobset can be evaluated:

<screen>
$ nix-build -I ~/src release.nix -A build
</screen>

The <varname>build</varname> job reuses the result of the
<varname>tarball</varname> job, rebuilding it only if it needs to.
</para>