# Contributing

Everybody is more than welcome to contribute to Oga, no matter how small the
change. To keep everything running smoothly there are a bunch of guidelines that
one should follow.

## General

* When changing code make sure to write RSpec tests for the changes.
* Document code using YARD. At the very least the method arguments and return
  value(s) should be documented.
* Use `raise` for raising errors instead of `fail`. You're raising errors after
  all, not failing them.

## Git

Git commits should have a <= 50 character summary, optionally followed by a
blank line and a more in depth description of 72 characters per line. For
example:

    Use blacklists/whitelists for HTML closing rules

    This allows for more fine grained control over when to close certain
    elements. For example, an unclosed <tr> element should be closed first
    when bumping into any element other than <td> or <th>. Using the old
    NodeNameSet this would mean having to list every possible HTML element
    out there. Using this new setup one can just create a whitelist of the
    <td> and <th> elements.

Please, _please_ write meaningful commit messages. Writing a good commit
messages is _just_ as important as writing good code. If you're having trouble
writing a commit message you should try to break the commits up into smaller
chunks. You can do so using a `git rebase`.

## Editor Setup

Use spaces for indentation, tabs are not accepted. The usage of spaces ensures
the indentation is identical no matter what program or system is used to view
the source code.

Hard wrap lines at 80 characters per line. Most modern editors can eaisly handle
this, if not you should get a better editor. For example, in Vim you can select
text in visual mode (using `v`) and press `gq` to automatically re-wrap the
selected text.

It's OK if a line is a few characters longer than 80 but _please_ keep it as
close to 80 characters as possible. Typically I do this when wrapping the line
results in several extra lines without it being much more readable.

I often have multiple windows vertically next to each other and 80 characters
per line is the only setup that lets me do so, even on smaller screen
resolutions. For example, my typical setup is 1 file browser and two vertical
windows. Using 80 characters per line ensures all code fits in that space along
with some slight padding to make reading more pleasant.

To make this process easier Oga comes with an [EditorConfig][editorconfig]
configuration file. If your editor supports this it will automatically apply
the required settings for you.

## Hacking on Oga

Before you start hacking on Oga make sure the following libraries/tools are
installed:

* Ragel 6.x (6.9 recommended)
* gunzip (to unpack the fixtures)
* javac (only when using JRuby)

Assuming you have the above tools installed and a local Git clone of Oga, lets
install the required Gems:

    bundle install

Next up, compile the required files and run the tests:

    rake

You can compile the various parsers/extensions by running:

    rake generate

For more information about the available tasks, run `rake -T`.

## Running Benchmarks

Benchmarks are located in the `benchmark` directory. Some of these require
fixture files which can be generated by running `rake fixtures`. Running a
benchmark is just a matter of running a Ruby script, for example:

    ruby benchmark/xml/parser/parser_bench.rb

## Tests

Tests are written using RSpec and use the "should" syntax instead of the
"expect" syntax (for as long as RSpec keeps supporting this). This means that
assertions are written as following:

    some_object.should == some_value

instead of this:

    expect(some_object).to eq(some_value)

Specification blocks should be written using `it`, grouping should be done using
`describe`. Specification descriptions should be meaningful and human friendly
English. For example:

    describe Oga::XML::Entities do
      describe 'decode' do
        it 'decodes &lt; into <' do
          # ...
        end
      end
    end

Typically the top-level `describe` block is used to describe a method name. In
such a case use `describe 'foo'` for class methods and `describe '#foo'` for
instance methods.

Do not use `let` for creating data re-used between specifications, instead use
a `before` block that sets an instance variable. In other words, use this:

    before do
      @number = 10
    end

instead of this:

    let(:number) { 10 }

Instance variables stand out much more and they don't require one to also
understand what exactly `let` does which in turn simplifies the process of
reading and writing specifications.

Whenever adding new specifications please keep them in the existing style unless
I indicate otherwise. There's nothing more annoying than inconsistent
specifications.

If you insist on changing the structure/style of specifications please open an
issue and ask about it _before_ making any changes. I am very picky about how I
want things and it would be a shame for somebody to spend hours working on
something that isn't going to be merged in any way.

## Continuous Integration

Two continuous integration services are used to ensure the tests of Oga pass
at all times:

* Travis CI: <https://travis-ci.org/YorickPeterse/oga>
* AppVeyor (Windows): <https://ci.appveyor.com/project/YorickPeterse/oga>

Please note that I will not accept patches that break any tests unless stated
otherwise.

## Extension Setup

Oga uses native extensions for the XML lexer. This is due to Ruby sadly not
being fast enough to chew through large amounts of XML (at least when using
Ragel). For example, the benchmark `benchmark/lexer/big_xml_time.rb` would take
around 6 seconds to complete on MRI 2.1.1. The native extensions on the other
hand can complete this benchmark in roughly 600 milliseconds.

Oga has two native extensions: one for MRI/Rubinius (written in C) and one for
JRuby (written in Java). Both extensions share the same Ragel grammar, found in
`ext/ragel/base_lexer.rl`. This grammar is set up in such a way that the syntax
is compatible with both C and Java. Specific details on how the grammar is used
can be found in the documentation of said grammar file.

The native extensions call back in to Ruby to actually perform the task of
creating tokens, validating input and so forth. As a result of this you'll most
likely never have to touch the C and/or Java code when changing the behaviour
of the lexer.

To compile the extensions run `rake generate` using your Ruby implementation of
choice. Note that extensions compiled for MRI can not be used on Rubinius and
vice-versa. To compile the JRuby extension you'll have to switch your active
Ruby version to JRuby first.

## Thread Safety

To ensure Oga remains thread-safe for as much as possible the usage of global
objects and/or state is forbidden. This means that you should _only_ use
constants/class methods for static/read-only data (e.g. an Array of static
Strings). In other words, this is fine:

    NUMBERS = [10, 20, 30]

    NUMBERS.each do |number|

    end

But this is not:

    TOOL = SomeFindReplaceTool.new

    output = TOOL.replace(input, 'foo', 'bar')

The exception here are libraries that are designed to be thread-safe, clearly
state this _and_ can prove it (e.g. by simply using a mutex). Even then global
state is highly frowned upon.

## Loading Libraries

All `require` calls should be placed in `lib/oga.rb`. Any `require` calls
specific to a Ruby implementation (e.g. JRuby) should be wrapped in a
conditional. For example:

    if RUBY_PLATFORM == 'java'
      org.foo.bar.baz.DoSomething()
    end

For loading files in Oga itself `require` should be used. _Don't_
modify `$LOAD_PATH`, instead run any scripts using `ruby -I lib`.

## Contact

In case you have any further questions or would like to receive feedback before
submitting a change, feel free to contact me. You can either open an issue,
send a tweet to [@yorickpeterse][twitter] or send an Email to
<yorickpeterse@gmail.com>.

[editorconfig]:http://editorconfig.org/
[twitter]: https://twitter.com/yorickpeterse