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8021b5241c
This adds changes to the rebar3 expression that patch rebar3 to force it to be hermetic. Now, by default, rebar3 literally can't download anything. A 'rebar3-open' expression was added for those folks whe want the normal rebar3.
306 lines
11 KiB
XML
306 lines
11 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="users-guide-to-the-erlang-infrastructure">
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<title>User's Guide to the Erlang Infrastructure</title>
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<section xml:id="build-tools">
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<title>Build Tools</title>
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<para>
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By default Rebar3 wants to manage it's own dependencies. In the
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normal non-Nix, this is perfectly acceptable. In the Nix world it
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is not. To support this we have created two versions of rebar3,
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<literal>rebar3</literal> and <literal>rebar3-open</literal>. The
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<literal>rebar3</literal> version has been patched to remove the
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ability to download anything from it. If you are not running it a
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nix-shell or a nix-build then its probably not going to work for
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you. <literal>rebar3-open</literal> is the normal, un-modified
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rebar3. It should work exactly as would any other version of
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rebar3. Any Erlang package should rely on
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<literal>rebar3</literal> and thats really what you should be
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using too.
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</para>
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</section>
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<section xml:id="how-to-install-erlang-packages">
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<title>How to install Erlang packages</title>
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<para>
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Erlang packages are not registered in the top level simply because
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they are not relevant to the vast majority of Nix users. They are
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installable using the <literal>erlangPackages</literal> attribute set.
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You can list the avialable packages in the
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<literal>erlangPackages</literal> with the following command:
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</para>
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<programlisting>
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$ nix-env -f "<nixpkgs>" -qaP -A erlangPackages
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erlangPackages.esqlite esqlite-0.2.1
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erlangPackages.goldrush goldrush-0.1.7
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erlangPackages.ibrowse ibrowse-4.2.2
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erlangPackages.jiffy jiffy-0.14.5
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erlangPackages.lager lager-3.0.2
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erlangPackages.meck meck-0.8.3
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erlangPackages.rebar3-pc pc-1.1.0
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</programlisting>
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<para>
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To install any of those packages into your profile, refer to them by
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their attribute path (first column):
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</para>
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<programlisting>
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$ nix-env -f "<nixpkgs>" -iA erlangPackages.ibrowse
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</programlisting>
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<para>
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The attribute path of any Erlang packages corresponds to the name
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of that particular package in Hex or its OTP Application/Release name.
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</para>
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</section>
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<section xml:id="packaging-erlang-applications">
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<title>Packaging Erlang Applications</title>
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<section xml:id="rebar3-packages">
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<title>Rebar3 Packages</title>
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<para>
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There is a Nix functional called
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<literal>buildRebar3</literal>. We use this function to make a
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derivation that understands how to build the rebar3 project. For
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example, the epression we use to build the <link
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xlink:href="https://github.com/erlang-nix/hex2nix">hex2nix</link>
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project follows.
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</para>
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<programlisting>
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{stdenv, fetchFromGitHub, buildRebar3, ibrowse, jsx, erlware_commons }:
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buildRebar3 rec {
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name = "hex2nix";
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version = "0.0.1";
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src = fetchFromGitHub {
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owner = "ericbmerritt";
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repo = "hex2nix";
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rev = "${version}";
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sha256 = "1w7xjidz1l5yjmhlplfx7kphmnpvqm67w99hd2m7kdixwdxq0zqg";
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};
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erlangDeps = [ ibrowse jsx erlware_commons ];
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}
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</programlisting>
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<para>
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The only visible difference between this derivation and
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something like <literal>stdenv.mkDerivation</literal> is that we
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have added <literal>erlangDeps</literal> to the derivation. If
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you add your Erlang dependencies here they will be correctly
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handled by the system.
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</para>
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<para>
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If your package needs to compile native code via Rebar's port
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compilation mechenism. You should add <literal>compilePort =
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true;</literal> to the derivation.
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</para>
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</section>
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<section xml:id="hex-packages">
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<title>Hex Packages</title>
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<para>
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Hex packages are based on Rebar packages. In fact, at the moment
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we can only compile Hex packages that are buildable with
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Rebar3. Packages that use Mix and other build systems are not
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supported. That being said, we know a lot more about Hex and can
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do more for you.
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</para>
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<programlisting>
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{ buildHex }:
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buildHex {
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name = "esqlite";
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version = "0.2.1";
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sha256 = "1296fn1lz4lz4zqzn4dwc3flgkh0i6n4sydg501faabfbv8d3wkr";
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compilePort = true;
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}
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</programlisting>
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<para>
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For Hex packages you need to provide the name, the version, and
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the Sha 256 digest of the package and use
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<literal>buildHex</literal> to build it. Obviously, the package
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needs to have already been published to Hex.
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</para>
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</section>
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</section>
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<section xml:id="how-to-develop">
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<title>How to develop</title>
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<section xml:id="accessing-an-environment">
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<title>Accessing an Environment</title>
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<para>
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Often, all you want to do is be able to access a valid
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environment that contains a specific package and its
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dependencies. we can do that with the <literal>env</literal>
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part of a derivation. For example, lets say we want to access an
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erlang repl with ibrowse loaded up. We could do the following.
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</para>
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<programlisting>
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~/w/nixpkgs ❯❯❯ nix-shell -A erlangPackages.ibrowse.env --run "erl"
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Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]
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Eshell V7.0 (abort with ^G)
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1> m(ibrowse).
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Module: ibrowse
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MD5: 3b3e0137d0cbb28070146978a3392945
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Compiled: January 10 2016, 23:34
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Object file: /nix/store/g1rlf65rdgjs4abbyj4grp37ry7ywivj-ibrowse-4.2.2/lib/erlang/lib/ibrowse-4.2.2/ebin/ibrowse.beam
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Compiler options: [{outdir,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/ebin"},
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debug_info,debug_info,nowarn_shadow_vars,
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warn_unused_import,warn_unused_vars,warnings_as_errors,
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{i,"/tmp/nix-build-ibrowse-4.2.2.drv-0/hex-source-ibrowse-4.2.2/_build/default/lib/ibrowse/include"}]
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Exports:
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add_config/1 send_req_direct/7
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all_trace_off/0 set_dest/3
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code_change/3 set_max_attempts/3
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get_config_value/1 set_max_pipeline_size/3
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get_config_value/2 set_max_sessions/3
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get_metrics/0 show_dest_status/0
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get_metrics/2 show_dest_status/1
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handle_call/3 show_dest_status/2
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handle_cast/2 spawn_link_worker_process/1
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handle_info/2 spawn_link_worker_process/2
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init/1 spawn_worker_process/1
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module_info/0 spawn_worker_process/2
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module_info/1 start/0
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rescan_config/0 start_link/0
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rescan_config/1 stop/0
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send_req/3 stop_worker_process/1
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send_req/4 stream_close/1
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send_req/5 stream_next/1
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send_req/6 terminate/2
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send_req_direct/4 trace_off/0
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send_req_direct/5 trace_off/2
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send_req_direct/6 trace_on/0
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trace_on/2
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ok
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2>
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</programlisting>
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<para>
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Notice the <literal>-A erlangPackages.ibrowse.env</literal>.That
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is the key to this functionality.
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</para>
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</section>
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<section xml:id="creating-a-shell">
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<title>Creating a Shell</title>
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<para>
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Getting access to an environment often isn't enough to do real
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development. Many times we need to create a
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<literal>shell.nix</literal> file and do our development inside
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of the environment specified by that file. This file looks a lot
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like the packageing described above. The main difference is that
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<literal>src</literal> points to project root and we call the
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package directly.
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</para>
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<programlisting>
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{ pkgs ? import "<nixpkgs"> {} }:
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with pkgs;
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let
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f = { buildHex, ibrowse, jsx, erlware_commons }:
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buildHex {
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name = "hex2nix";
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version = "0.1.0";
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src = ./.;
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erlangDeps = [ ibrowse jsx erlware_commons ];
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};
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drv = erlangPackages.callPackage f {};
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in
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drv
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</programlisting>
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<section xml:id="building-in-a-shell">
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<title>Building in a shell</title>
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<para>
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Unfortunatly for us users of Nix, Rebar isn't very cooperative
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with us from the standpoint of building a hermetic
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environment. When building the rebar3 support we had to do some
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sneaky things to get it not to go out and pull packages on its
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own. Also unfortunately, you have to do some of the same things
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when building a project inside of a Nix shell.
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<orderedlist numeration="arabic">
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<listitem>
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<para>Run <literal>rebar3-nix-bootstrap</literal> every time
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dependencies change</para>
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</listitem>
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<listitem>
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<para>Set Home to the current directory.</para>
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</listitem>
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</orderedlist>
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If you do these two things then Rebar will be happy with you. I
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codify these into a makefile. Forunately, rebar3-nix-bootstrap
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is idempotent and fairly quick. so you can run it as often as
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you like.
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</para>
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<programlisting>
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# =============================================================================
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# Rules
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# =============================================================================
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.PHONY= all test clean repl shell build test analyze bootstrap
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all: test
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clean:
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rm -rf _build
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rm -rf .cache
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repl:
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nix-shell --run "erl"
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shell:
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nix-shell --run "bash"
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bootstrap:
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nix-shell --pure --run "rebar3-nix-bootstrap"
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build: bootstrap
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nix-shell --pure --run "HOME=$(CURDIR) rebar3 compile"
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analyze: bootstrap
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nix-shell --pure --run "HOME=$(CURDIR) rebar3 do compile,dialyzer"
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test: bootstrap
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nix-shell --pure --run "HOME=$(CURDIR) rebar3 do compile,dialyzer,eunit"
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</programlisting>
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<para>
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If you add the <literal>shell.nix</literal> as described and
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user rebar as follows things should simply work.
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</para>
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</section>
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</section>
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</section>
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<section xml:id="generating-packages-from-hex-with-hex2nix">
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<title>Generating Packages from Hex with Hex2Nix</title>
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<para>
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Updating the Hex packages requires the use of the
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<literal>hex2nix</literal> tool. Given the path to the Erlang
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modules (usually
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<literal>pkgs/development/erlang-modules</literal>). It will
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happily dump a file called
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<literal>hex-packages.nix</literal>. That file will contain all
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the packages that use a recognized build system in Hex. However,
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it can't know whether or not all those packages are buildable.
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</para>
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<para>
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To make life easier for our users, it makes good sense to go
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ahead and attempt to build all those packages and remove the
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ones that don't build. To do that, simply run the command (in
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the root of your <literal>nixpkgs</literal> repository). that follows.
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</para>
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<programlisting>
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$ nix-build -A erlangPackages
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</programlisting>
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<para>
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That will build every package in
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<literal>erlangPackages</literal>. Then you can go through and
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manually remove the ones that fail. Hopefully, someone will
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improve <literal>hex2nix</literal> in the future to automate
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that.
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</para>
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</section>
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</chapter>
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