Update release notes

Also add some examples to nix --help.

1 files changed, 729 insertions, 254 deletions

diff --git a/doc/manual/release-notes/rl-2.0.xml b/doc/manual/release-notes/rl-2.0.xml
index effd2e39d..0ad17373e 100644
--- a/doc/manual/release-notes/rl-2.0.xml
+++ b/doc/manual/release-notes/rl-2.0.xml
@@ -6,165 +6,572 @@
 
 <title>Release 2.0 (2018-02-??)</title>
 
-<para>This release has the following new features:</para>
+<para>The following incompatible changes have been made:</para>
 
 <itemizedlist>
 
   <listitem>
-    <para>Start of new <command>nix</command> command line
-    interface. This is a work in progress and the interface is subject
-    to change.</para>
+    <para>The manifest-based substituter mechanism
+    (<command>download-using-manifests</command>) has been <link
+    xlink:href="https://github.com/NixOS/nix/commit/867967265b80946dfe1db72d40324b4f9af988ed">removed</link>. It
+    has been superseded by the binary cache substituter mechanism
+    since several years. As a result, the following programs have been
+    removed:
 
     <itemizedlist>
+      <listitem><para><command>nix-pull</command></para></listitem>
+      <listitem><para><command>nix-generate-patches</command></para></listitem>
+      <listitem><para><command>bsdiff</command></para></listitem>
+      <listitem><para><command>bspatch</command></para></listitem>
+    </itemizedlist>
+    </para>
+  </listitem>
 
-      <listitem><para>Self-documenting: <option>--help</option> shows
-      all available command-line arguments.</para></listitem>
-
-      <listitem><para><option>--help-config</option> shows all
-      configuration options.</para></listitem>
+  <listitem>
+    <para>The “copy from other stores” substituter mechanism
+    (<command>copy-from-other-stores</command> and the
+    <envar>NIX_OTHER_STORES</envar> environment variable) has been
+    removed. It was primarily used by the NixOS installer to copy
+    available paths from the installation medium. The replacement is
+    to use a chroot store as a substituter
+    (e.g. <literal>--substituters /mnt</literal>), or to build into a
+    chroot store (e.g. <literal>--store /mnt --substituter /</literal>).</para>
+  </listitem>
 
-      <listitem><para><command>nix build</command>: Replacement for
-      <command>nix-build</command>.</para></listitem>
+  <listitem>
+    <para>The command <command>nix-push</command> has been removed as
+    part of the effort to eliminate Nix's dependency on Perl. You can
+    use <command>nix copy</command> instead, e.g. <literal>nix copy
+    --to /tmp/my-binary-cache <replaceable>paths…</replaceable></literal></para>
+  </listitem>
 
-      <listitem><para><command>nix ls-store</command> and <command>nix
-      ls-nar</command> allow listing the contents of a store path or
-      NAR file.</para></listitem>
+  <listitem>
+    <para>The “nested” log output feature (<option>--log-type
+    pretty</option>) has been removed. As a result,
+    <command>nix-log2xml</command> was also removed.</para>
+  </listitem>
 
-      <listitem><para><command>nix cat-store</command> and
-      <command>nix cat-nar</command> allow extracting a file from a
-      store path or NAR file.</para></listitem>
+  <listitem>
+    <para>OpenSSL-based signing has been <link
+    xlink:href="https://github.com/NixOS/nix/commit/f435f8247553656774dd1b2c88e9de5d59cab203">removed</link>. This
+    feature was never well-supported. A better alternative is provided
+    by the <option>secret-key-files</option> and
+    <option>trusted-public-keys</option> options.</para>
+  </listitem>
 
-      <listitem><para><command>nix verify</command> checks whether a
-      store path is unmodified and/or is trusted.</para></listitem>
+  <listitem>
+    <para>Failed build caching has been <link
+    xlink:href="https://github.com/NixOS/nix/commit/8cffec84859cec8b610a2a22ab0c4d462a9351ff">removed</link>. This
+    feature was introduced to support the Hydra continuous build
+    system, but Hydra no longer uses it.</para>
+  </listitem>
 
-      <listitem><para><command>nix copy-sigs</command> copies
-      signatures from one store to another.</para></listitem>
+  <listitem>
+    <para><filename>nix-mode.el</filename> has been removed from
+    Nix. It is now <link
+    xlink:href="https://github.com/NixOS/nix-mode">a separate
+    repository</link> and can be installed through the MELPA package
+    repository.</para>
+  </listitem>
 
-      <listitem><para><command>nix sign-paths</command> signs store
-      paths.</para></listitem>
+</itemizedlist>
 
-      <listitem><para><command>nix copy</command> copies paths between
-      arbitrary Nix stores, generalising
-      <command>nix-copy-closure</command> and
-      <command>nix-push</command>.</para></listitem>
+<para>This release has the following new features:</para>
 
-      <listitem><para><command>nix path-info</command> shows
-      information about store paths.</para></listitem>
+<itemizedlist>
 
-      <listitem><para><command>nix run</command> starts a shell in
-      which the specified packages are available.</para></listitem>
+  <listitem>
+    <para>It introduces a new command named <command>nix</command>,
+    which is intended to eventually replace all
+    <command>nix-*</command> commands with a more consistent and
+    better designed user interface. It currently provides replacements
+    for some (but not all) of the functionality provided by
+    <command>nix-store</command>, <command>nix-build</command>,
+    <command>nix-shell -p</command>, <command>nix-env -qa</command>,
+    <command>nix-instantiate --eval</command>,
+    <command>nix-push</command> and
+    <command>nix-copy-closure</command>. It has the following major
+    features:</para>
 
-      <listitem><para><command>nix log</command> shows the build log
-      of a package or path. If the build log is not available locally,
-      it will try to obtain it from a binary cache.</para></listitem>
+    <itemizedlist>
 
-      <listitem><para><command>nix eval</command> replaces
-      <command>nix-instantiate --eval</command>.</para></listitem>
+      <listitem>
+        <para>Unlike the legacy commands, it has a consistent way to
+        refer to packages and package-like argumements (like store
+        paths). For example, the following commands all copy the GNU
+        Hello package to a remote machine:
+
+        <screen>nix copy --to ssh://machine nixpkgs.hello</screen>
+        <screen>nix copy --to ssh://machine /nix/store/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9-hello-2.10</screen>
+        <screen>nix copy --to ssh://machine '(with import &lt;nixpkgs> {}; hello)'</screen>
+
+        By contrast, <command>nix-copy-closure</command> only accepted
+        store paths as arguments.</para>
+      </listitem>
+
+      <listitem>
+        <para>It is self-documenting: <option>--help</option> shows
+        all available command-line arguments. If
+        <option>--help</option> is given after a subcommand, it shows
+        examples for that subcommand. <command>nix
+        --help-config</command> shows all configuration
+        options.</para>
+      </listitem>
+
+      <listitem>
+        <para>It is much less verbose. By default, it displays a
+        single-line progress indicator that shows how many packages
+        are left to be built or downloaded, and (if there are running
+        builds) the most recent line of builder output. If a build
+        fails, it shows the last few lines of builder output. The full
+        build log can be retrieved using <command>nix
+        log</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para>It <link
+        xlink:href="https://github.com/NixOS/nix/commit/b8283773bd64d7da6859ed520ee19867742a03ba">provides</link>
+        all <filename>nix.conf</filename> configuration options as
+        command line flags. For example, instead of <literal>--option
+        http-connections 100</literal> you can write
+        <literal>--http-connections 100</literal>. Boolean options can
+        be written as
+        <literal>--<replaceable>foo</replaceable></literal> or
+        <literal>--no-<replaceable>foo</replaceable></literal>
+        (e.g. <option>--no-auto-optimise-store</option>).</para>
+      </listitem>
+
+      <listitem>
+        <para>Many subcommands have a <option>--json</option> flag to
+        write results to stdout in JSON format.</para>
+      </listitem>
 
-      <listitem><para><command>nix dump-path</command> to get a NAR
-      from a store path.</para></listitem>
+    </itemizedlist>
 
-      <listitem><para><command>nix edit</command> opens the source
-      code of a package in an editor.</para></listitem>
+    <warning><para>Please note that the <command>nix</command> command
+    is a work in progress and the interface is subject to
+    change.</para></warning>
 
-      <listitem><para><command>nix search</command> replaces
-      <command>nix-env -qa</command>. It searches the available
-      packages for occurences of a search string in the attribute
-      name, package name or description. It caches available packages
-      to speed up searches.</para></listitem>
+    <para>It provides the following high-level (“porcelain”)
+    subcommands:</para>
 
-      <listitem><para><command>nix why-depends</command> (d41c5eb13f4f3a37d80dbc6d3888644170c3b44a).</para></listitem>
+    <itemizedlist>
 
-      <listitem><para><command>nix show-derivation</command> (e8d6ee7c1b90a2fe6d824f1a875acc56799ae6e2).</para></listitem>
+      <listitem>
+        <para><command>nix build</command> is a replacement for
+        <command>nix-build</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix run</command> executes a command in an
+        environment in which the specified packages are available. It
+        is (roughly) a replacement for <command>nix-shell
+        -p</command>. Unlike that command, it does not execute the
+        command in a shell, and has a flag (<command>-c</command>)
+        that specifies the unquoted command line to be
+        executed.</para>
+
+        <para>It is particularly useful in conjunction with chroot
+        stores, allowing Linux users who do not have permission to
+        install Nix in <command>/nix/store</command> to still use
+        binary substitutes that assume
+        <command>/nix/store</command>. For example,
+
+        <screen>nix run --store ~/my-nix nixpkgs.hello -c hello --greeting 'Hi everybody!'</screen>
+
+        downloads (or if not substitutes are available, builds) the
+        GNU Hello package into
+        <filename>~/my-nix/nix/store</filename>, then runs
+        <command>hello</command> in a mount namespace where
+        <filename>~/my-nix/nix/store</filename> is mounted onto
+        <command>/nix/store</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix search</command> replaces <command>nix-env
+        -qa</command>. It searches the available packages for
+        occurences of a search string in the attribute name, package
+        name or description. Unlike <command>nix-env -qa</command>, it
+        has a cache to speed up subsequent searches.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix copy</command> copies paths between
+        arbitrary Nix stores, generalising
+        <command>nix-copy-closure</command> and
+        <command>nix-push</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix repl</command> replaces the external
+        program <command>nix-repl</command>. It provides an
+        interactive environment for evaluating and building Nix
+        expressions. Note that it uses <literal>linenoise-ng</literal>
+        instead of GNU Readline.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix upgrade-nix</command> upgrades Nix to the
+        latest stable version. This requires that Nix is installed in
+        a profile. (Thus it won’t work on NixOS, or if it’s installed
+        outside of the Nix store.)</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix verify</command> checks whether store paths
+        are unmodified and/or “trusted” (see below). It replaces
+        <command>nix-store --verify</command> and <command>nix-store
+        --verify-path</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix log</command> shows the build log of a
+        package or path. If the build log is not available locally, it
+        will try to obtain it from the configured substituters (such
+        as <uri>cache.nixos.org</uri>, which now provides build
+        logs).</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix edit</command> opens the source code of a
+        package in your editor.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix eval</command> replaces
+        <command>nix-instantiate --eval</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command
+        xlink:href="https://github.com/NixOS/nix/commit/d41c5eb13f4f3a37d80dbc6d3888644170c3b44a">nix
+        why-depends</command> shows why one store path has another in
+        its closure. This is primarily useful to finding the causes of
+        closure bloat. For example,
+
+        <screen>nix why-depends nixpkgs.vlc nixpkgs.libdrm.dev</screen>
+
+        shows a chain of files and fragments of file contents that
+        cause the VLC package to have the “dev” output of
+        <literal>libdrm</literal> in its closure — an undesirable
+        situation.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix path-info</command> shows information about
+        store paths, replacing <command>nix-store -q</command>. A
+        useful feature is the option <option>--closure-size</option>
+        (<option>-S</option>). For example, the following command show
+        the closure sizes of every path in the current NixOS system
+        closure, sorted by size:
+
+        <screen>nix path-info -rS /run/current-system | sort -nk2</screen>
+
+        </para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix optimise-store</command> replaces
+        <command>nix-store --optimise</command>. The main difference
+        is that it has a progress indicator.</para>
+      </listitem>
 
-      <listitem><para><command>nix add-to-store</command> (970366266b8df712f5f9cedb45af183ef5a8357f).</para></listitem>
+    </itemizedlist>
 
-      <listitem><para><command>nix upgrade-nix</command> upgrades Nix
-      to the latest stable version. This requires that Nix is
-      installed in a profile. (Thus it won’t work on NixOS, or if it’s
-      installed outside of the Nix store.)</para></listitem>
+    <para>A number of low-level (“plumbing”) commands are also
+    available:</para>
 
-      <listitem><para>Progress indicator.</para></listitem>
+    <itemizedlist>
 
-      <listitem><para>All options are available as flags now
-      (b8283773bd64d7da6859ed520ee19867742a03ba).</para></listitem>
+      <listitem>
+        <para><command>nix ls-store</command> and <command>nix
+        ls-nar</command> list the contents of a store path or NAR
+        file. The former is primarily useful in conjunction with
+        remote stores, e.g.
+
+        <screen>nix ls-store --store https://cache.nixos.org/ -lR /nix/store/0i2jd68mp5g6h2sa5k9c85rb80sn8hi9-hello-2.10</screen>
+
+        lists the contents of path in a binary cache.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix cat-store</command> and <command>nix
+        cat-nar</command> allow extracting a file from a store path or
+        NAR file.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix dump-path</command> writes the contents of
+        a store path to stdout in NAR format. This replaces
+        <command>nix-store --dump</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command
+        xlink:href="https://github.com/NixOS/nix/commit/e8d6ee7c1b90a2fe6d824f1a875acc56799ae6e2">nix
+        show-derivation</command> displays a store derivation in JSON
+        format. This is an alternative to
+        <command>pp-aterm</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command
+        xlink:href="https://github.com/NixOS/nix/commit/970366266b8df712f5f9cedb45af183ef5a8357f">nix
+        add-to-store</command> replaces <command>nix-store
+        --add</command>.</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix sign-paths</command> signs store
+        paths. (TODO: add examples)</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix copy-sigs</command> copies signatures from
+        one store to another. (TODO: add examples and
+        tests)</para>
+      </listitem>
+
+      <listitem>
+        <para><command>nix show-config</command> shows all
+        configuration options and their current values.</para>
+      </listitem>
 
     </itemizedlist>
 
   </listitem>
 
   <listitem>
-    <para>The external program <command>nix-repl</command> has been
-    integrated into Nix as <command>nix repl</command>.</para>
-  </listitem>
+    <para>The store abstraction that Nix has had for a long time to
+    support store access via the Nix daemon has been extended
+    significantly. In particular, substituters (which used to be
+    external programs such as
+    <command>download-from-binary-cache</command>) are now subclasses
+    of the abstract <classname>Store</classname> class. This allows
+    many Nix commands to operate on such store types. For example,
+    <command>nix path-info</command> shows information about paths in
+    your local Nix store, while <command>nix path-info --store
+    https://cache.nixos.org/</command> shows information about paths
+    in the specified binary cache. Similarly,
+    <command>nix-copy-closure</command>, <command>nix-push</command>
+    and substitution are all instances of the general notion of
+    copying paths between different kinds of Nix stores.</para>
 
-  <listitem>
-    <para>If a fixed-output derivation produces a result with an
-    incorrect hash, the output path will be moved to the location
-    corresponding to the actual hash and registered as valid. Thus, a
-    subsequent build of the fixed-output derivation with the correct
-    hash is unnecessary.</para>
-  </listitem>
+    <para>Stores are specified using an URI-like syntax,
+    e.g. <uri>https://cache.nixos.org/</uri> or
+    <uri>ssh://machine</uri>. The following store types are supported:
+
+    <itemizedlist>
+
+      <listitem>
+
+        <para><classname>LocalStore</classname> (stori URI
+        <literal>local</literal> or an absolute path) and the misnamed
+        <classname>RemoteStore</classname> (<literal>daemon</literal>)
+        provide access to a local Nix store, the latter via the Nix
+        daemon. You can use <literal>auto</literal> or the empty
+        string to auto-select a local or daemon store depending on
+        whether you have write permission to the Nix store. It is no
+        longer necessary to set the <envar>NIX_REMOTE</envar>
+        environment variable to use the Nix daemon.</para>
+
+        <para>As noted above, <classname>LocalStore</classname> now
+        supports chroot builds, allowing the “physical” location of
+        the Nix store
+        (e.g. <filename>/home/alice/nix/store</filename>) to differ
+        from its “logical” location (typically
+        <filename>/nix/store</filename>). This allows non-root users
+        to use Nix while still getting the benefits from prebuilt
+        binaries from <uri>cache.nixos.org</uri>.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>BinaryCacheStore</classname> is the abstract
+        superclass of all binary cache stores. It supports writing
+        build logs and NAR content listings in JSON format.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>HttpBinaryCacheStore</classname>
+        (<literal>http://</literal>, <literal>https://</literal>)
+        supports binary caches via HTTP or HTTPS. If the server
+        supports <literal>PUT</literal> requests, it supports
+        uploading store paths via commands such as <command>nix
+        copy</command>.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>LocalBinaryCacheStore</classname>
+        (<literal>file://</literal>) supports binary caches in the
+        local filesystem.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>S3BinaryCacheStore</classname>
+        (<literal>s3://</literal>) supports binary caches stored in
+        Amazon S3, if enabled at compile time.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>LegacySSHStore</classname> (<literal>ssh://</literal>)
+        is used to implement remote builds and
+        <command>nix-copy-closure</command>.</para>
+
+      </listitem>
+
+      <listitem>
+
+        <para><classname>SSHStore</classname>
+        (<literal>ssh-ng://</literal>) supports arbitrary Nix
+        operations on a remote machine via the same protocol used by
+        <command>nix-daemon</command>.</para>
+
+      </listitem>
+
+    </itemizedlist>
+
+    </para>
 
-  <listitem>
-    <para>It is no longer necessary to set the
-    <envar>NIX_REMOTE</envar> environment variable if you need to use
-    the Nix daemon. Nix will use the daemon automatically if you don’t
-    have write access to the Nix database.</para>
   </listitem>
 
   <listitem>
-    <para>The Nix language now supports floating point numbers. They are
-    based on regular C++ <literal>float</literal> and compatible with
-    existing integers and number-related operations. Export and import to and
-    from JSON and XML works, too.</para>
+
+    <para>Security has been improved in various ways:
+
+    <itemizedlist>
+
+      <listitem>
+        <para>Nix now stores signatures for local store
+        paths. When paths are copied between stores (e.g., copied from
+        a binary cache to a local store), signatures are
+        propagated.</para>
+
+        <para>Locally-built paths are signed automatically using the
+        secret keys specified by the <option>secret-key-files</option>
+        store option. Secret/public key pairs can be generated using
+        <command>nix-store
+        --generate-binary-cache-key</command>. (TODO: rename)</para>
+
+        <para>In addition, locally-built store paths are marked as
+        “ultimately trusted”, but this bit is not propagated when
+        paths are copied between stores.</para>
+      </listitem>
+
+      <listitem>
+        <para>Content-addressable store paths no longer require
+        signatures — they can be imported into a store by unprivileged
+        users even if they lack signatures.</para>
+      </listitem>
+
+      <listitem>
+        <para>The command <command>nix verify</command> checks whether
+        the specified paths are trusted, i.e., have a certain number
+        of trusted signatures, are ultimately trusted, or are
+        content-addressed.</para>
+      </listitem>
+
+      <listitem>
+        <para>Substitutions from binary caches <link
+        xlink:href="https://github.com/NixOS/nix/commit/ecbc3fedd3d5bdc5a0e1a0a51b29062f2874ac8b">now</link>
+        require signatures by default. This was already the case on
+        NixOS.</para>
+      </listitem>
+
+      <listitem>
+        <para>In Linux sandbox builds, we <link
+        xlink:href="https://github.com/NixOS/nix/commit/eba840c8a13b465ace90172ff76a0db2899ab11b">now</link>
+        use <filename>/build</filename> instead of
+        <filename>/tmp</filename> as the temporary build
+        directory. This fixes potential security problems when a build
+        accidentally stores its <envar>TMPDIR</envar> in some
+        security-sensitive place, such as an RPATH.</para>
+      </listitem>
+
+    </itemizedlist>
+
+    </para>
+
   </listitem>
 
   <listitem>
-    <para><command>nix-shell</command> now sets the
-    <varname>IN_NIX_SHELL</varname> environment variable during
-    evaluation and in the shell itself. This can be used to perform
-    different actions depending on whether you’re in a Nix shell or in
-    a regular build. Nixpkgs provides
-    <varname>lib.inNixShell</varname> to check this variable during
-    evaluation. (bb36a1a3cf3fbe6bc9d0afcc5fa0f928bed03170)</para>
+    <para><emphasis>Pure evaluation mode</emphasis>. This is a variant
+    of the existing restricted evaluation mode. In pure mode, the Nix
+    evaluator forbids access to anything that could cause different
+    evaluations of the same command line arguments to produce a
+    different result. This includes builtin functions such as
+    <function>builtins.getEnv</function>, but more importantly,
+    <emphasis>all</emphasis> filesystem or network access unless a
+    content hash or commit hash is specified. For example, calls to
+    <function>builtins.fetchGit</function> are only allowed if a
+    <varname>rev</varname> attribute is specified.</para>
+
+    <para>The goal of this feature is to enable true reproducibility
+    and traceability of builds (including NixOS system configurations)
+    at the evaluation level. For example, in the future,
+    <command>nixos-rebuild</command> might build configurations from a
+    Nix expression in a Git repository in pure mode. That expression
+    might fetch other repositories such as Nixpkgs via
+    <function>builtins.fetchGit</function>. The commit hash of the
+    top-level repository then uniquely identifies a running system,
+    and, in conjunction with that repository, allows it to be
+    reproduced or modified.</para>
+
   </listitem>
 
   <listitem>
-    <para>Internal: all <classname>Store</classname> classes are now
-    thread-safe. <classname>RemoteStore</classname> supports multiple
-    concurrent connections to the daemon. This is primarily useful in
-    multi-threaded programs such as
-    <command>hydra-queue-runner</command>.</para>
+    <para>There are several new features to support binary
+    reproducibility (i.e. to help ensure that multiple builds of the
+    same derivation produce exactly the same output). When
+    <option>enforce-determinism</option> is set to
+    <literal>false</literal>, it’s <link
+    xlink:href="https://github.com/NixOS/nix/commit/8bdf83f936adae6f2c907a6d2541e80d4120f051">no
+    longer</link> a fatal error if build rounds produce different
+    output. Also, a hook named <option>diff-hook</option> is <link
+    xlink:href="https://github.com/NixOS/nix/commit/9a313469a4bdea2d1e8df24d16289dc2a172a169w">provided</link>
+    to allow you to run tools such as <command>diffoscope</command>
+    when build rounds produce different output.</para>
   </listitem>
 
   <listitem>
-    <para>The dependency on Perl has been removed. As a result, some
-    (obsolete) programs have been removed: <command>nix-push</command>
-    (replaced by <command>nix copy</command>),
-    <command>nix-pull</command> (obsoleted by binary caches),
-    <command>nix-generate-patches</command>,
-    <command>bsdiff</command>, <command>bspatch</command>.</para>
+    <para>Configuring remote builds is a lot easier now. Provided you
+    are not using the Nix daemon, you can now just specify a remote
+    build machine on the command line, e.g. <literal>--option builders
+    'ssh://my-mac x86_64-darwin'</literal>. The environment variable
+    <envar>NIX_BUILD_HOOK</envar> has been removed and is no longer
+    needed. The environment variable <envar>NIX_REMOTE_SYSTEMS</envar>
+    is still supported for compatibility, but it is also possible to
+    specify builders in <command>nix.conf</command> by setting the
+    option <literal>builders =
+    @<replaceable>path</replaceable></literal>.</para>
   </listitem>
 
   <listitem>
-    <para>Improved store abstraction. Substituters
-    eliminated. BinaryCacheStore, LocalBinaryCacheStore,
-    HttpBinaryCacheStore, S3BinaryCacheStore (compile-time
-    optional), SSHStore. Add docs + examples?
-    </para>
+    <para>If a fixed-output derivation produces a result with an
+    incorrect hash, the output path is moved to the location
+    corresponding to the actual hash and registered as valid. Thus, a
+    subsequent build of the fixed-output derivation with the correct
+    hash is unnecessary.</para>
   </listitem>
 
   <listitem>
-    <para>Nix now stores signatures for local store
-    paths. Locally-built paths are now signed automatically using the
-    secret keys specified by the <option>secret-key-files</option>
-    store option.</para>
-
-    <para>In addition, store paths that have been built locally are
-    marked as “ultimately trusted”, and content-addressable store
-    paths carry a “content-addressability assertion” that allow them
-    to be trusted without any signatures.</para>
+    <para><command>nix-shell</command> <link
+    xlink:href="https://github.com/NixOS/nix/commit/ea59f39326c8e9dc42dfed4bcbf597fbce58797c">now</link>
+    sets the <varname>IN_NIX_SHELL</varname> environment variable
+    during evaluation and in the shell itself. This can be used to
+    perform different actions depending on whether you’re in a Nix
+    shell or in a regular build. Nixpkgs provides
+    <varname>lib.inNixShell</varname> to check this variable during
+    evaluation.</para>
   </listitem>
 
   <listitem>
@@ -179,7 +586,8 @@
     <uri>https://nixos.org/channels/<replaceable>channel-name</replaceable>/nixexprs.tar.xz</uri>. For
     example, <literal>nix-build channel:nixos-15.09 -A hello</literal>
     will build the GNU Hello package from the
-    <literal>nixos-15.09</literal> channel.</para>
+    <literal>nixos-15.09</literal> channel. In the future, this may
+    use Git to fetch updates more efficiently.</para>
   </listitem>
 
   <listitem>
@@ -189,45 +597,119 @@
   </listitem>
 
   <listitem>
-    <para><function>builtins.fetchGit</function>.
-    (38539b943a060d9cdfc24d6e5d997c0885b8aa2f)</para>
+    <para>Networking has been improved:
+
+    <itemizedlist>
+
+      <listitem>
+        <para>HTTP/2 is now supported. This makes binary cache lookups
+        <link
+        xlink:href="https://github.com/NixOS/nix/commit/90ad02bf626b885a5dd8967894e2eafc953bdf92">much
+        more efficient</link>.</para>
+      </listitem>
+
+      <listitem>
+        <para>We now retry downloads on many HTTP errors, making
+        binary caches substituters more resilient to temporary
+        failures.</para>
+      </listitem>
+
+      <listitem>
+        <para>HTTP credentials can now be configured via the standard
+        <filename>netrc</filename> mechanism.</para>
+      </listitem>
+
+      <listitem>
+        <para>If S3 support is enabled at compile time,
+        <uri>s3://</uri> URIs are <link
+        xlink:href="https://github.com/NixOS/nix/commit/9ff9c3f2f80ba4108e9c945bbfda2c64735f987b">supported</link>
+        in all places where Nix allows URIs.</para>
+      </listitem>
+
+      <listitem>
+        <para>Brotli compression is now supported. In particular,
+        <uri>cache.nixos.org</uri> build logs are now compressed using
+        Brotli.</para>
+      </listitem>
+
+    </itemizedlist>
+
+    </para>
+
   </listitem>
 
   <listitem>
-    <para><literal>&lt;nix/fetchurl.nix&gt;</literal> now uses the
-    content-addressable tarball cache at
-    <uri>http://tarballs.nixos.org/</uri>, just like
-    <function>fetchurl</function> in
-    Nixpkgs. (f2682e6e18a76ecbfb8a12c17e3a0ca15c084197)</para>
+    <para><command>nix-env</command> <link
+    xlink:href="https://github.com/NixOS/nix/commit/b0cb11722626e906a73f10dd9a0c9eea29faf43a">now</link>
+    ignores packages with bad derivation names (in particular those
+    starting with a digit or containing a dot).</para>
   </listitem>
 
   <listitem>
-    <para>Chroot Nix stores: allow the “physical” location of the Nix
-    store (e.g. <filename>/home/alice/nix/store</filename>) to differ
-    from its “logical” location (typically
-    <filename>/nix/store</filename>). This allows non-root users to
-    use Nix while still getting the benefits from prebuilt binaries
-    from
-    <uri>cache.nixos.org</uri>. (4494000e04122f24558e1436e66d20d89028b4bd,
-    3eb621750848e0e6b30e5a79f76afbb096bb6c8a)</para>
+    <para>Many configuration options have been renamed, either because
+    they were unnecessarily verbose
+    (e.g. <option>build-use-sandbox</option> is now just
+    <option>sandbox</option>) or to reflect generalised behaviour
+    (e.g. <option>binary-caches</option> is now
+    <option>substituters</option> because it allows arbitrary store
+    URIs). The old names are still supported for compatibility.</para>
   </listitem>
 
   <listitem>
-    <para>On Linux, builds are now executed in a user
-    namespace with uid 1000 and gid 100.</para>
+    <para>The <option>max-jobs</option> option can <link
+    xlink:href="https://github.com/NixOS/nix/commit/7251d048fa812d2551b7003bc9f13a8f5d4c95a5">now</link>
+    be set to <literal>auto</literal> to use the number of CPUs in the
+    system.</para>
   </listitem>
 
   <listitem>
-    <para><function>builtins.fetchurl</function> and
-    <function>builtins.fetchTarball</function> now support
-    <varname>sha256</varname> and <varname>name</varname>
-    attributes.</para>
+    <para>Hashes can <link
+    xlink:href="https://github.com/NixOS/nix/commit/c0015e87af70f539f24d2aa2bc224a9d8b84276b">now</link>
+    be specified in base-64 format, in addition to base-16 and the
+    non-standard base-32.</para>
   </listitem>
 
   <listitem>
-    <para><literal>HttpBinaryCacheStore</literal> (the replacement of
-    <command>download-from-binary-cache</command>) now retries
-    automatically on certain HTTP error codes.</para>
+    <para><command>nix-shell</command> now uses
+    <varname>bashInteractive</varname> from Nixpkgs, rather than the
+    <command>bash</command> command that happens to be in the caller’s
+    <envar>PATH</envar>. This is especially important on macOS where
+    the <command>bash</command> provided by the system is seriously
+    outdated and cannot execute <literal>stdenv</literal>’s setup
+    script.</para>
+  </listitem>
+
+  <listitem>
+    <para>Nix can now automatically trigger a garbage collection if
+    free disk space drops below a certain level during a build. This
+    is configured using the <option>min-free</option> and
+    <option>max-free</option> options.</para>
+  </listitem>
+
+  <listitem>
+    <para><command>nix-store -q --roots</command> and
+    <command>nix-store --gc --print-roots</command> now show temporary
+    and in-memory roots.</para>
+  </listitem>
+
+  <listitem>
+    <para>
+      Nix can now be extended with plugins. See the documentation of
+      the <option>plugin-files</option> option for more details.
+    </para>
+  </listitem>
+
+</itemizedlist>
+
+<para>The Nix language has the following new features:
+
+<itemizedlist>
+
+  <listitem>
+    <para>It supports floating point numbers. They are based on the
+    C++ <literal>float</literal> type and are supported by the
+    existing numerical operators. Export and import to and from JSON
+    and XML works, too.</para>
   </listitem>
 
   <listitem>
@@ -245,194 +727,187 @@ configureFlags = "--prefix=${placeholder "out"} --includedir=${placeholder "dev"
     add docs.</para>
   </listitem>
 
-  <listitem>
-    <para>Support for HTTP/2. This makes binary cache lookups much
-    more efficient. (90ad02bf626b885a5dd8967894e2eafc953bdf92)</para>
-  </listitem>
+</itemizedlist>
 
-  <listitem>
-    <para>The <option>build-sandbox-paths</option> configuration
-    option can now specify optional paths by appending a
-    <literal>?</literal>, e.g. <literal>/dev/nvidiactl?</literal> will
-    bind-mount <varname>/dev/nvidiactl</varname> only if it
-    exists.</para>
-  </listitem>
+</para>
 
-  <listitem>
-    <para>More support for testing build reproducibility: when
-    <option>enforce-determinism</option> is set to
-    <literal>false</literal>, it’s no longer a fatal error build
-    rounds produce different output
-    (8bdf83f936adae6f2c907a6d2541e80d4120f051); add a hook to run
-    diffoscope when build rounds produce different output
-    (9a313469a4bdea2d1e8df24d16289dc2a172a169w).</para>
-  </listitem>
+<para>The following builtin functions are new or extended:
 
-  <listitem>
-    <para>Kill builds as soon as stdout/stderr is closed. This fixes a
-    bug that allowed builds to hang Nix indefinitely (regardless of
-    timeouts). (21948deed99a3295e4d5666e027a6ca42dc00b40)</para>
-  </listitem>
+<itemizedlist>
 
   <listitem>
-    <para>Add support for passing structured data to builders. TODO:
-    document. (6de33a9c675b187437a2e1abbcb290981a89ecb1)</para>
-  </listitem>
+    <para><function
+    xlink:href="https://github.com/NixOS/nix/commit/38539b943a060d9cdfc24d6e5d997c0885b8aa2f">builtins.fetchGit</function>
+    allows Git repositories to be fetched at evaluation time. Thus it
+    differs from the <function>fetchgit</function> function in
+    Nixpkgs, which fetches at build time and cannot be used to fetch
+    Nix expressions during evaluation. A typical use case is to import
+    external NixOS modules from your configuration, e.g.
 
-  <listitem>
-    <para><varname>exportReferencesGraph</varname>: Export more
-    complete info in JSON
-    format. (c2b0d8749f7e77afc1c4b3e8dd36b7ee9720af4a)</para>
-  </listitem>
+    <programlisting>imports = [ (builtins.fetchGit https://github.com/edolstra/dwarffs + "/module.nix") ];</programlisting>
 
-  <listitem>
-    <para>Support for
-    netrc. (e6e74f987f0fa284d220432d426eb965269a97d6,
-    302386f775eea309679654e5ea7c972fb6e7b9af)</para>
+    </para>
   </listitem>
 
   <listitem>
-    <para>Support <uri>s3://</uri> URIs in all places where Nix allows
-    URIs. (9ff9c3f2f80ba4108e9c945bbfda2c64735f987b)</para>
+    <para>Similarly, <function>builtins.fetchMercurial</function>
+    allows you to fetch Mercurial repositories.</para>
   </listitem>
 
   <listitem>
-    <para>The <option>build-max-jobs</option> option can be set to
-    <literal>auto</literal> to use the number of CPUs in the
-    system. (7251d048fa812d2551b7003bc9f13a8f5d4c95a5)</para>
+    <para><function>builtins.path</function> generalises
+    <function>builtins.filterSource</function> and path literals
+    (e.g. <literal>./foo</literal>). It allows specifying a store path
+    name that differs from the source path name
+    (e.g. <literal>builtins.path { path = ./foo; name = "bar";
+    }</literal>) and also supports filtering out unwanted
+    files.</para>
   </listitem>
 
   <listitem>
-    <para>Add support for Brotli compression.
-    <uri>cache.nixos.org</uri> compresses build logs using
-    Brotli.</para>
+    <para><function>builtins.fetchurl</function> and
+    <function>builtins.fetchTarball</function> now support
+    <varname>sha256</varname> and <varname>name</varname>
+    attributes.</para>
   </listitem>
 
   <listitem>
-    <para>Substitutions from binary caches now require signatures by
-    default. This was already the case on
-    NixOS. (ecbc3fedd3d5bdc5a0e1a0a51b29062f2874ac8b)</para>
+    <para><function
+    xlink:href="https://github.com/NixOS/nix/commit/b8867a0239b1930a16f9ef3f7f3e864b01416dff">builtins.split</function>
+    splits a string using a POSIX extended regular expression as the
+    separator.</para>
   </listitem>
 
   <listitem>
-    <para><command>nix-env</command> now ignores packages with bad
-    derivation names (in particular those starting with a digit or
-    containing a
-    dot). (b0cb11722626e906a73f10dd9a0c9eea29faf43a)</para>
+    <para><function
+    xlink:href="https://github.com/NixOS/nix/commit/26d92017d3b36cff940dcb7d1611c42232edb81a">builtins.partition</function>
+    partitions the elements of a list into two lists, depending on a
+    Boolean predicate.</para>
   </listitem>
 
   <listitem>
-    <para>Renamed various configuration options. (TODO: in progress)</para>
+    <para><literal>&lt;nix/fetchurl.nix&gt;</literal> now uses the
+    content-addressable tarball cache at
+    <uri>http://tarballs.nixos.org/</uri>, just like
+    <function>fetchurl</function> in
+    Nixpkgs. (f2682e6e18a76ecbfb8a12c17e3a0ca15c084197)</para>
   </listitem>
 
   <listitem>
-    <para>Remote machines can now be specified on the command
-    line. TODO:
-    document. (1a68710d4dff609bbaf61db3e17a2573f0aadf17)</para>
+    <para>In restricted and pure evaluation mode, builtin functions
+    that download from the network (such as
+    <function>fetchGit</function>) are permitted to fetch underneath a
+    list of URI prefixes specified in the option
+    <option>allowed-uris</option>.</para>
   </listitem>
 
-  <listitem>
-    <para>In Linux sandbox builds, we now use
-    <filename>/build</filename> instead of <filename>/tmp</filename>
-    as the temporary build directory. This fixes potential security
-    problems when a build accidentally stores its
-    <envar>TMPDIR</envar> in some critical place, such as an
-    RPATH. (eba840c8a13b465ace90172ff76a0db2899ab11b)</para>
-  </listitem>
+</itemizedlist>
 
-  <listitem>
-    <para>In Linux sandbox builds, we now provide a default
-    <filename>/bin/sh</filename> (namely <filename>ash</filename> from
-    BusyBox). (a2d92bb20e82a0957067ede60e91fab256948b41)</para>
-  </listitem>
+</para>
 
-  <listitem>
-    <para>Make all configuration options available as command line
-    flags (b8283773bd64d7da6859ed520ee19867742a03ba).</para>
-  </listitem>
+<para>The Nix build environment has the following changes:
 
-  <listitem>
-    <para>Support base-64
-    hashes. (c0015e87af70f539f24d2aa2bc224a9d8b84276b)</para>
-  </listitem>
+<itemizedlist>
 
   <listitem>
-    <para><command>nix-shell</command> now uses
-    <varname>bashInteractive</varname> from Nixpkgs, rather than the
-    <command>bash</command> command that happens to be in the caller’s
-    <envar>PATH</envar>. This is especially important on macOS where
-    the <command>bash</command> provided by the system is seriously
-    outdated and cannot execute <literal>stdenv</literal>’s setup
-    script.</para>
+    <para>Values such as Booleans, integers, (nested) lists and
+    attribute sets can <link
+    xlink:href="https://github.com/NixOS/nix/commit/6de33a9c675b187437a2e1abbcb290981a89ecb1">now</link>
+    be passed to builders in a non-lossy way. If the special attribute
+    <varname>__structuredAttrs</varname> is set to
+    <literal>true</literal>, the other derivation attributes are
+    serialised in JSON format and made available to the builder via
+    the file <envar>.attrs.json</envar> in the builder’s temporary
+    directory. This obviates the need for
+    <varname>passAsFile</varname> since JSON files have no size
+    restrictions, unlike process environments.</para>
+
+    <para><link
+    xlink:href="https://github.com/NixOS/nix/commit/2d5b1b24bf70a498e4c0b378704cfdb6471cc699">As
+    a convenience to Bash builders</link>, Nix writes a script named
+    <envar>.attrs.sh</envar> to the builder’s directory that
+    initialises shell variables corresponding to all attributes that
+    are representable in Bash. This includes non-nested (associative)
+    arrays. For example, the attribute <literal>hardening.format =
+    true</literal> ends up as the Bash associative array element
+    <literal>${hardening[format]}</literal>.</para>
+  </listitem>
+
+  <listitem>
+    <para>Builders can <link
+    xlink:href="https://github.com/NixOS/nix/commit/88e6bb76de5564b3217be9688677d1c89101b2a3">now</link>
+    communicate what build phase they are in by writing messages to
+    the file descriptor specified in <envar>NIX_LOG_FD</envar>. The
+    current phase is shown by the <command>nix</command> progress
+    indicator.
+    </para>
   </listitem>
 
   <listitem>
-    <para>New builtin functions: <function>builtins.split</function>
-    (b8867a0239b1930a16f9ef3f7f3e864b01416dff),
-    <function>builtins.partition</function>.</para>
+    <para>In Linux sandbox builds, we <link
+    xlink:href="https://github.com/NixOS/nix/commit/a2d92bb20e82a0957067ede60e91fab256948b41">now</link>
+    provide a default <filename>/bin/sh</filename> (namely
+    <filename>ash</filename> from BusyBox).</para>
   </listitem>
 
   <listitem>
-    <para>Automatic garbage collection.</para>
+    <para>In structured attribute mode,
+    <varname>exportReferencesGraph</varname> <link
+    xlink:href="https://github.com/NixOS/nix/commit/c2b0d8749f7e77afc1c4b3e8dd36b7ee9720af4a">exports</link>
+    extended information about closures in JSON format. In particular,
+    it includes the sizes and hashes of paths. This is primarily
+    useful for NixOS image builders.</para>
   </listitem>
 
   <listitem>
-    <para><command>nix-store -q --roots</command> and
-    <command>nix-store --gc --print-roots</command> now show temporary
-    and in-memory roots.</para>
+    <para>Builds are <link
+    xlink:href="https://github.com/NixOS/nix/commit/21948deed99a3295e4d5666e027a6ca42dc00b40">now</link>
+    killed as soon as Nix receives EOF on the builder’s stdout or
+    stderr. This fixes a bug that allowed builds to hang Nix
+    indefinitely, regardless of
+    timeouts.</para>
   </listitem>
 
   <listitem>
-    <para>Builders can now communicate what build phase they are in by
-    writing messages to the file descriptor specified in
-    <envar>NIX_LOG_FD</envar>. (88e6bb76de5564b3217be9688677d1c89101b2a3)
-    </para>
+    <para>The <option>sandbox-paths</option> configuration
+    option can now specify optional paths by appending a
+    <literal>?</literal>, e.g. <literal>/dev/nvidiactl?</literal> will
+    bind-mount <varname>/dev/nvidiactl</varname> only if it
+    exists.</para>
   </listitem>
 
   <listitem>
-    <para>
-      Nix can now be extended with plugins. See the documentation of
-      the 'plugin-files' option for more details.
-    </para>
+    <para>On Linux, builds are now executed in a user
+    namespace with uid 1000 and gid 100.</para>
   </listitem>
 
 </itemizedlist>
 
-<para>Some features were removed:</para>
-
-<itemizedlist>
-
-  <listitem>
-    <para>“Nested” log output. As a result,
-    <command>nix-log2xml</command> was also removed.</para>
-  </listitem>
+</para>
 
-  <listitem>
-    <para>OpenSSL-based signing. (f435f8247553656774dd1b2c88e9de5d59cab203)</para>
-  </listitem>
+<para>A number of significant internal changes were made:
 
-  <listitem>
-    <para>Caching of failed
-    builds. (8cffec84859cec8b610a2a22ab0c4d462a9351ff)</para>
-  </listitem>
+<itemizedlist>
 
   <listitem>
-    <para><filename>nix-mode.el</filename> has been removed from
-    Nix. It is now a separate repository in
-    <uri>https://github.com/NixOS/nix-mode</uri> and can be installed
-    through the MELPA package repository.</para>
+    <para>Nix no longer depends on Perl and all Perl components have
+    been rewritten in C++ or removed. The Perl bindings that used to
+    be part of Nix have been moved to a separate package,
+    <literal>nix-perl</literal>.</para>
   </listitem>
 
   <listitem>
-    <para>In restricted evaluation mode
-    (<option>--restrict-eval</option>), builtin functions that
-    download from the network (such as <function>fetchGit</function>)
-    are permitted to fetch underneath the list of URI prefixes
-    specified in the option <option>allowed-uris</option>.</para>
+    <para>All <classname>Store</classname> classes are now
+    thread-safe. <classname>RemoteStore</classname> supports multiple
+    concurrent connections to the daemon. This is primarily useful in
+    multi-threaded programs such as
+    <command>hydra-queue-runner</command>.</para>
   </listitem>
 
 </itemizedlist>
 
+</para>
+
 <para>This release has contributions from TBD.</para>
 
 </section>