nix-prefetch-url: Support unpacking tarballs

This allows nix-prefetch-url to prefetch the output of fetchzip and
its wrappers (like fetchFromGitHub). For example:

  $ nix-prefetch-url --unpack https://github.com/NixOS/patchelf/archive/0.8.tar.gz

or from a Nix expression:

  $ nix-prefetch-url -A nix-repl.src

In the latter case, --unpack can be omitted because nix-repl.src is a
fetchFromGitHub derivation and thus has "outputHashMode" set to
"recursive".

1 files changed, 16 insertions, 1 deletions

diff --git a/doc/manual/command-ref/nix-prefetch-url.xml b/doc/manual/command-ref/nix-prefetch-url.xml
index 9cbaa42a1b1f..e1f0c8e5447c 100644
--- a/doc/manual/command-ref/nix-prefetch-url.xml
+++ b/doc/manual/command-ref/nix-prefetch-url.xml
@@ -81,6 +81,16 @@ downloaded file in the Nix store is also printed.</para>
 
   </varlistentry>
 
+  <varlistentry><term><option>--unpack</option></term>
+
+    <listitem><para>Unpack the archive (which must be a tarball or zip
+    file) and add the result to the Nix store. The resulting hash can
+    be used with functions such as Nixpkgs’s
+    <varname>fetchzip</varname> or
+    <varname>fetchFromGitHub</varname>.</para></listitem>
+
+  </varlistentry>
+
 </variablelist>
 
 </refsection>
@@ -94,7 +104,12 @@ $ nix-prefetch-url ftp://ftp.gnu.org/pub/gnu/hello/hello-2.10.tar.gz
 
 $ nix-prefetch-url --print-path mirror://gnu/hello/hello-2.10.tar.gz
 0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
-/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz</screen>
+/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
+
+$ nix-prefetch-url --unpack --print-path https://github.com/NixOS/patchelf/archive/0.8.tar.gz
+079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7
+/nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0.8.tar.gz
+</screen>
 
 </refsection>