Fork opal/opal on GitHub, then clone the fork to your machine:
$ git clone git://github.com/<YOUR-GITHUB-USERNAME>/opal.git
Setup the project:
$ bin/setup
Run the test suite:
$ bundle exec rake
You are now ready to make your first contribution to Opal! At a high level, your workflow will be to:
- Make changes to Opal source code
- Run the test suite to make sure it still passes
- Submit a pull request
Before making changes to Opal source, you need to understand a little about how the test suite works. Every spec that Opal test suite executes is listed in spec/ruby_specs file. Each line in that file is a path to either a spec file or a directory full of spec files. If it's a path to a directory, all spec files in that directory will be executed when you run the test suite. Lines starting with a ! represent files that are excluded (i.e. "execute all files in a given directory, except this file"), and lines starting with a # are ignored as comments. All paths are relative to the top-level specs directory. Let's follow one of these paths - ruby/core/string/sub_spec - and see where it goes.
Navigating to spec/ruby/core directory, you see that it contains multiple sub-directories, usually named after the Ruby class or module. Drilling further down into spec/ruby/core/string you see all the spec files for the various String behaviors under test, usually named by a method name followed by _spec.rb. Opening spec/ruby/core/string/sub_spec.rb you finally see the code that checks the correctness of Opal's implementation of the String#sub method's behavior.
When you execute $ bundle exec rake, the code in this file is executed, along with all the other specs in the entire test suite. It's a good idea to run the entire test suite when you feel you reached a certain milestone in the course of making your changes (exactly what that means is up to you), and definitely do $ bundle exec rake before commiting your changes to make sure they have not introduced regressions or other unintended side effects.
But you will want to run tests as often as possible, after every small change, and running the entire test suite will slow you down. You need to be able to execute a single spec that is concerned with the feature you are currently working on. To accomplish this, just add PATTERN to your spec invocation command, like this:
$ bundle exec rake mspec_ruby_nodejs PATTERN=spec/ruby/core/string/sub_spec.rb
This will make sure that only spec/ruby/core/string/sub_spec.rb is run, and no other specs are executed. Globs can be used too:
$ bundle exec rake mspec_ruby_nodejs PATTERN="spec/ruby/core/string/*_spec.rb"
Another way to quickly validate ideas and play with your changes is to use opal-repl, a tool similar to irb. Running opal-repl drops you into an interactive environment with your current version of Opal loaded, including any changes you have made.
$ bundle exec opal-repl
>> 2 + 2
=> 4
>>
When quickly iterating on an idea, even opal-repl may feel a bit too heavy, because after making a change in Opal, you must exit from opal-repl and do $ bundle exec opal-repl again to load Opal with your latest changes. In this case, you can run opal with the -e option, which executes a piece of code you pass to it once, then returns to the shell. This means that in order to run it again after making another adjustment to Opal, all you have to do is hit the up arrow key on your keyboard and press the enter key. This is the fastest way to go from making a change in Opal to seeing its effect.
$ bundle exec opal -e "3.times {puts 'hello'}"
hello
hello
hello
$
Let's recap what we covered so far. spec/ruby_specs is the "master list" of all the specs that get executed when you do $ bundle exec rake. You know where to find individual specs, inspect them, and execute them selectively or in bulk. But how do you know which specs to work on? You may be tempted to compare the contents of one of the directories in spec/ruby/core with the list of paths in spec/ruby_specs, add the missing paths to the "master list", run $ bundle exec rake, and start fixing the failures by implementing the missing features. However, chances are that as you are reading this, there are plenty of failing tests in the specs that are already listed in spec/ruby_specs. How can that be if $ bundle exec rake runs green? To understand this, you need to get acquainted with the concept of spec filters.
There are two types of spec filters in the Opal project: spec/filters/bugs and spec/filters/unsupported. Both filters have the same effect: any spec failures that are noted inside any of the files inside of these directories are ignored when running the spec suite, i.e. they are not reported as failures. Even though their effect is the same, the purpose of bugs and unsupported filters is different. As the name suggests, unsupported filters list permanent failures, things that other Ruby implementations can do that Opal cannot and will never be able to do (by design and by virtue of being implemented on top of JavaScript running in the browser environment). bugs filters, on the other hand, are temporary failures, problems that need to be worked on. Problems that Opal needs your help with. Think of the bugs directory and the files contained within it as your "TO DO" list for contributing to Opal.
Comment out any of the fail lines in any of the files in the spec/filters/bugs directory, run $bundle exec rake, and watch it fail. Make it pass and submit a pull request - that's all there is to it :) Happy hacking!
Core classes use each other and your changes may fix other bugs in spec/filters/bugs. If you think it's possible, run an inverted test suite by providing environment variable INVERT_RUNNING_MODE=true:
$ env INVERT_RUNNING_MODE=true RUBYSPECS=true PATTERN="spec/ruby/core/string/*_spec.rb" rake mspec_ruby_nodejs
This command will execute tests marked as "bugs" from every file in the spec/ruby/core/string directory. After running it you will get a list of specs that in fact are passing. Feel free to remove them from spec/filters/bugs.
Note: Opal has some bugs that may cause a shared state between tests. Sometimes green specs are green only in the inverted test suite, so after removing them from /bugs, run a regular test suite one more time to verify that everything is fine.
Also there are some specs in spec/ruby/language/while_spec.rb that cause an infinite loop. Make sure to comment them before running a whole inverted test suite.
There are two ways to benchmark Opal's performance: one way is to write a program (or a set of programs) that takes sufficently long time to execute, then measure the execution time, and the other is to execute a specific Ruby Spec Suite example (or a set of examples) multiple times, then measure the execution time. Let's call the former "Traditional Benchmarking", and the latter "The Ruby Spec Suite Benchmarking".
Regardless of which of the two types of benchmarking above you happen to be doing, the reporting of benchmark results works the same way: bundle exec rake bench:report.
It's important to understand that benchmarking in Opal works on the principle of a single, shared benchmarking workspace, a bench, where the results of each benchmark run that you perform get automatically saved. When you do bundle exec rake bench:report, you get a combined report of all of the benchmark results that are currently sitting in your workspace. This means you can check out an older commit, run benchmarks, checkout a newer commit, run benchmarks, then run the report to see the results from the two commits side-by-side. After you're done, (or before starting a new benchmarking session), you can do bundle exec rake bench:clear to reset your workspace to a clean slate.
You can get a list of all the available benchmarking commands by running bundle exec rake -T | grep bench as shown below.
$ bundle exec rake -T | grep bench
rake bench:clear # Delete all benchmark results
rake bench:opal # Benchmark Opal
rake bench:report # Combined report of all benchmark results
rake bench:ruby # Benchmark Ruby
At the root of the opal project tree is a folder called benchmark that contains a file called benchmarks. This file lists all of the benchmarks that will be run if you do bundle exec bench:opal without specifying any particular benchmark file(s) as parameters to this rake task. In the example below, I pick which benchmarks to run by passing their file paths as parameters to the rake task.
Start with a clean slate:
$ bundle exec rake bench:clear
rm tmp/bench/*
Run two benchmark programs from the MRI benchmarking suite by passing their file paths as parameters: (Note: passing params to Rake tasks is tricky - notice there is no space after the comma!)
$ bundle exec rake bench:opal[test/cruby/benchmark/bm_app_answer.rb,test/cruby/benchmark/bm_app_factorial.rb]
bundle exec opal benchmark/run.rb test/cruby/benchmark/bm_app_answer.rb test/cruby/benchmark/bm_app_factorial.rb | tee tmp/bench/Opal1
test/cruby/benchmark/bm_app_answer.rb 0.7710001468658447
test/cruby/benchmark/bm_app_factorial.rb 0.0820000171661377
===============================================
Executed 2 benchmarks in 0.8530001640319824 sec
In this case, I want to see how Opal's results stack up against MRI's results, so I will run the same set of benchmarks for Ruby:
$ bundle exec rake bench:ruby[test/cruby/benchmark/bm_app_answer.rb,test/cruby/benchmark/bm_app_factorial.rb]
bundle exec ruby benchmark/run.rb test/cruby/benchmark/bm_app_answer.rb test/cruby/benchmark/bm_app_factorial.rb | tee tmp/bench/Ruby1
test/cruby/benchmark/bm_app_answer.rb 0.04913724200014258
test/cruby/benchmark/bm_app_factorial.rb 1.3288652799965348
===============================================
Executed 2 benchmarks in 1.3780025219966774 sec
Now I'm ready to see the result of the two runs side-by-side:
$ bundle exec rake bench:report
Benchmark Opal1 Ruby1
test/cruby/benchmark/bm_app_answer.rb 0.771 0.049
test/cruby/benchmark/bm_app_factorial.rb 0.082 1.329
If I were to continue running benchmarks, more columns would be added to the report. You can select which columns you want to display (and in what order) by passing their names as params to the rake task like so: bundle exec rake bench:report[Ruby1,Opal1]
This type of benchmarking relies on a feature of MSpec whereby you can ask it to execute every example in a given spec multiple times. Adding BM=<number of times> to your regular spec suite invocation command will hook into this MSpec functionality, collect timing information, and dump the results into the benchmarking workspace, making them available for reporting. Below is an example run with a single spec and BM set to 100, meaning each example in the spec would be run 100 times.
$ bundle exec rake mspec_ruby_nodejs PATTERN=spec/ruby/core/array/permutation_spec.rb BM=100
...
Benchmark results have been written to tmp/bench/Spec1
To view the results, run bundle exec rake bench:report
Now let's see the report: (Spec names can be very long, scroll to the right to see the numbers)
$ bundle exec rake bench:report
Benchmark Spec1
Array#permutation_returns_an_Enumerator_of_all_permutations_when_called_without_a_block_or_arguments 0.117
Array#permutation_returns_an_Enumerator_of_permutations_of_given_length_when_called_with_an_argument_but_no_block 0.064
Array#permutation_yields_all_permutations_to_the_block_then_returns_self_when_called_with_block_but_no_arguments 0.076
Array#permutation_yields_all_permutations_of_given_length_to_the_block_then_returns_self_when_called_with_block_and_argument 0.072
Array#permutation_returns_the_empty_permutation_([[]])_when_the_given_length_is_0 0.029
Array#permutation_returns_the_empty_permutation([])_when_called_on_an_empty_Array 0.029
Array#permutation_returns_no_permutations_when_the_given_length_has_no_permutations 0.029
Array#permutation_handles_duplicate_elements_correctly 0.081
Array#permutation_handles_nested_Arrays_correctly 0.085
Array#permutation_truncates_Float_arguments 0.063
Array#permutation_returns_an_Enumerator_which_works_as_expected_even_when_the_array_was_modified 0.056
Array#permutation_generates_from_a_defensive_copy,_ignoring_mutations 0.038
Opal relies on the parser gem, see debug/development documentation there to know more about its internals: https://whitequark.github.io/parser/.