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Allows rebar to work with "alien" sub_dirs and deps
Erlang Java
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Rebar Alien Plugin

This plugin allows you to include alien sub_dirs and/or dependencies in a project built by rebar. In practise, this means that the plugin can do two things for you:

  1. Allow you to work with sub_dirs that do not have an OTP .app file
  2. Allow you to deal with custom behaviours for any kind of sub_dirs

To see how this works, take a look at the examples directory, which contains a sub directory including a simple junit test and maven build. You can run the example (assuming you have java + maven installed on your system) by changing to the examples/simple directory and typing:

$ rebar compile

If you pass -v you'll get more verbose output.

Going into examples/custom you will find a more complete sample, which does the same thing, but using a more general approach to the plugin configuration.

Try running rebar alien-commands to list the available commands and then running the special mvn:test command which is added (via configuration!) to rebar only for the inttest subfolder. The choice of mvn:test as a command name was intended to mirror the command being passed to maven.

$ rebar alien-commands
==> inttest (alien-commands)
Commands for Alien Directory inttest:
* alien-commands              list Alien commands
* alien-clean                 clean Alien artefacts

Commands for Alien Directory inttest:
* mvn:test                    Run Maven Tests
$ rebar mvn:test
==> inttest (mvn:test)
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building Test Demo
[INFO]    task-segment: [clean, test]
[INFO] ------------------------------------------------------------------------
[INFO] [clean:clean {execution: default-clean}]
[INFO] Deleting directory /Users/t4/work/hyperthunk/rebar_alien_plugin/examples/custom/inttest/target
[INFO] [resources:resources {execution: default-resources}]
[WARNING] Using platform encoding (MacRoman actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/t4/work/hyperthunk/rebar_alien_plugin/examples/custom/inttest/src/main/resources
[INFO] [compiler:compile {execution: default-compile}]
[INFO] No sources to compile
[INFO] [resources:testResources {execution: default-testResources}]
[WARNING] Using platform encoding (MacRoman actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/t4/work/hyperthunk/rebar_alien_plugin/examples/custom/inttest/src/test/resources
[INFO] [compiler:testCompile {execution: default-testCompile}]
[INFO] Compiling 1 source file to /Users/t4/work/hyperthunk/rebar_alien_plugin/examples/custom/inttest/target/test-classes
[INFO] [surefire:test {execution: default-test}]
[INFO] Surefire report directory: /Users/t4/work/hyperthunk/rebar_alien_plugin/examples/custom/inttest/target/surefire-reports

 T E S T S
Running org.nebularis.demos.TestDemo
Test Ok!

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.023 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3 seconds
[INFO] Finished at: Sat Sep 24 00:10:23 BST 2011
[INFO] Final Memory: 13M/784M
[INFO] ------------------------------------------------------------------------
==> custom (mvn:test)

How it works

The plugin looks in your rebar.config for a list of sub-directories to process, under the alien_dirs configuration element. For each of these directories, the plugin will ensure that a valid OTP application file (i.e., a template in the src/<project>.app.src) is created if not already present.

Secondly, the plugin will look in your rebar.config for any additional build instructions in the alien_conf element. These instructions must take one of the following forms:

  • {mkdir, Dest} which creates the specified directory
  • {create, Dest, Data} which creates a file Dest with the contents Data
  • {copy, Src, Dest} which copies Src to Dest
  • {link, Src, Alias} creates a symlink on supported platforms, copies otherwise
  • {chmod, Target, Mode} change file mode(s) in Target
  • {exec, Cmd} some arbitrary shell command to run in the directory
  • {exec, Cmd, Opts} as (4), but with options passed to the shell environment
  • {make, Options} runs make:all/1 in the directory
  • {call, {M,F,A} evaluates apply/3 with the supplied MFA tuple
  • {call, {M,F,A,dir}} as (7), but prepends the current directory to A
  • {call, {M,F,A}, Extra} as (8), passes Extra to code:add_pathsa/1 first
  • {rule, Test, Action} applies Action only if Test passes
  • {command, Name, Desc, RulesOrActions} creates a new rebar command

These instructions allow you to generate, copy or otherwise insert your own custom rebar configuration into the target directory. The simple project skeleton in examples uses this mechanism to push a set of custom post_hooks into the inttest folder, which instruct rebar to run the mvn clean test command and execute the alien tests.

The {command, ...} form creates a new rebar command, mapped to the supplied set of actions/rules. See examples/custom for the usage pattern.

Running rebar alien:clean will undo any actions specified in alien_conf (i.e., it will delete any generated/copied files and folder) and remove any rebar.config that was generated in src/<project>.app.src on your behalf.

Usage Examples

The rebar_alien_plugin's purpose is to help you avoid writing plugins unless you actually need reusable functionality across projects. Local (source loaded) plugins are very useful, but for many simple tasks just using configuration is cleaner and more maintainable.

Here is an example that runs some simple sanity checks. The code isn't part of the main build, nor the automated test suites, but it's useful to keep a copy of it and having a separate project/sub_dir really seems like overkill.

{plugins, [rebar_alien_plugin]}.
{alien_dirs, ["checks"]}.
{alien_conf, [
    {"checks", [
        {command, 'sanity_checks', "Build + Run Sanity Checks", [
            %% compile the sources in the 'checks' folder
            {make, [load]},
            %% evaluate sanity_checks:run/0 with extra dirs on the path
            {call, {sanity_checks, run, []}, [".", "../ebin"]}

This example is taken from another project. The custom spec-compile command is being used to download and install a testing framework for C source code, which wouldn't be possible using standard rebar depedencies. It then uses this alien tool chain to turn test specifications into source code, which in turn is compiled to produce a binary. The second spec-test command simply executes the compiled binary to run the tests.

%% *alien_dirs get treated like local sub_dirs at runtime*
{alien_dirs, ["spec"]}.
{alien_conf, [
    {"spec", [
        %% we're adding some new rebar commands here

        {command, 'spec-compile', "build cspec and all tests", [
            %% rebar get-deps doesn't support non-OTP sources,
            %% so we end up doing a fetch and install by hand
            {rule, "cspec",
                {exec, "git clone cspec"}},
            {rule, "cspec/bin/cspec", {exec, "make -C cspec"}},
            {rule, "c_src", {mkdir, "c_src"}},
            {rule, "bin", {mkdir, "bin"}},
            %% the rule returns true when any member of B in {A, B} has a
            %% newer timestamp than any member of A
            {rule, {"c_src/edbc_oci_specs.c", "spec/*.spec"},
                %% TODO: make this work on win32 ;)
                {exec, "cat spec/*.spec | cspec/bin/cspec > c_src/edbc_oci_specs.c"}},

            {rule, {"bin/edbc_oci_specs", "c_src/edbc_oci_specs.c"},
                %% TODO: use the libconf/cc module to generate this
                {exec, "cc -Icspec/src cspec/build/cspec.o c_src/edbc_oci_specs.c "
                       "-o bin/edbc_oci_specs"}}
        {command, 'spec-test', "run all test specs", [
            {exec, "bin/edbc_oci_specs"}

%% these config elements are only processed by running 'alien:clean'
{alien_clean, [
    {"spec", ["spec/cspec"]}

Doing this with pre_hooks is cumbersome and the configuration effectively creates a full blown build plugin on the fly, for minimal effort.


The rebar_alien_plugin requires a recent version rebar with support for plugins hooking into the Module:preprocess/2 mechanism.

Include the following tuple in your rebar deps:

{deps, [{rebar_alien_plugin, ".*", {git,
    "git://", "master"}}]}.

Then you will be able to fetch and install the plugin (locally) with rebar:

user@host$ rebar get-deps compile
user@host$ rebar dist skip_deps=true

Alternatively, you may put the plugin into your ERL_LIBS path somewhere and use it in many projects. This can be done manually, or using a package manager:

user@host$ epm install hyperthunk/rebar_alien_plugin    # or
user@host$ sutro install hyperthunk/rebar_alien_plugin  # or
user@host$ agner install rebar_alien_plugin
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