<section xmlns="http://docbook.org/ns/docbook"
      xmlns:xlink="http://www.w3.org/1999/xlink"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      version="5.0"
      xml:id="ssec-relnotes-2.2">

<title>Release 2.2 (2019-01-11)</title>

<para>This is primarily a bug fix release. It also has the following
changes:</para>

<itemizedlist>

  <listitem>
    <para>In derivations that use structured attributes (i.e. that
    specify set the <varname>__structuredAttrs</varname> attribute to
    <literal>true</literal> to cause all attributes to be passed to
    the builder in JSON format), you can now specify closure checks
    per output, e.g.:

<programlisting>
outputChecks."out" = {
  # The closure of 'out' must not be larger than 256 MiB.
  maxClosureSize = 256 * 1024 * 1024;

  # It must not refer to C compiler or to the 'dev' output.
  disallowedRequisites = [ stdenv.cc "dev" ];
};

outputChecks."dev" = {
  # The 'dev' output must not be larger than 128 KiB.
  maxSize = 128 * 1024;
};
</programlisting>

    </para>
  </listitem>


  <listitem>
    <para>The derivation attribute
    <varname>requiredSystemFeatures</varname> is now enforced for
    local builds, and not just to route builds to remote builders.
    The supported features of a machine can be specified through the
    configuration setting <varname>system-features</varname>.</para>

    <para>By default, <varname>system-features</varname> includes
    <literal>kvm</literal> if <filename>/dev/kvm</filename>
    exists. For compatibility, it also includes the pseudo-features
    <literal>nixos-test</literal>, <literal>benchmark</literal> and
    <literal>big-parallel</literal> which are used by Nixpkgs to route
    builds to particular Hydra build machines.</para>

  </listitem>

  <listitem>
    <para>Sandbox builds are now enabled by default on Linux.</para>
  </listitem>

  <listitem>
    <para>The new command <command>nix doctor</command> shows
    potential issues with your Nix installation.</para>
  </listitem>

  <listitem>
    <para>The <literal>fetchGit</literal> builtin function now uses a
    caching scheme that puts different remote repositories in distinct
    local repositories, rather than a single shared repository. This
    may require more disk space but is faster.</para>
  </listitem>

  <listitem>
    <para>The <literal>dirOf</literal> builtin function now works on
    relative paths.</para>
  </listitem>

  <listitem>
    <para>Nix now supports <link
    xlink:href="https://www.w3.org/TR/SRI/">SRI hashes</link>,
    allowing the hash algorithm and hash to be specified in a single
    string. For example, you can write:

<programlisting>
import &lt;nix/fetchurl.nix> {
  url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
  hash = "sha256-XSLa0FjVyADWWhFfkZ2iKTjFDda6mMXjoYMXLRSYQKQ=";
};
</programlisting>

    instead of

<programlisting>
import &lt;nix/fetchurl.nix> {
  url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
  sha256 = "5d22dad058d5c800d65a115f919da22938c50dd6ba98c5e3a183172d149840a4";
};
</programlisting>

    </para>

    <para>In fixed-output derivations, the
    <varname>outputHashAlgo</varname> attribute is no longer mandatory
    if <varname>outputHash</varname> specifies the hash.</para>

    <para><command>nix hash-file</command> and <command>nix
    hash-path</command> now print hashes in SRI format by
    default. They also use SHA-256 by default instead of SHA-512
    because that's what we use most of the time in Nixpkgs.</para>
  </listitem>

  <listitem>
    <para>Integers are now 64 bits on all platforms.</para>
  </listitem>

  <listitem>
    <para>The evaluator now prints profiling statistics (enabled via
    the <envar>NIX_SHOW_STATS</envar> and
    <envar>NIX_COUNT_CALLS</envar> environment variables) in JSON
    format.</para>
  </listitem>

  <listitem>
    <para>The option <option>--xml</option> in <command>nix-store
    --query</command> has been removed. Instead, there now is an
    option <option>--graphml</option> to output the dependency graph
    in GraphML format.</para>
  </listitem>

  <listitem>
    <para>All <filename>nix-*</filename> commands are now symlinks to
    <filename>nix</filename>. This saves a bit of disk space.</para>
  </listitem>

  <listitem>
    <para><command>nix repl</command> now uses
    <literal>libeditline</literal> or
    <literal>libreadline</literal>.</para>
  </listitem>

</itemizedlist>

</section>