Add Ruby MRI linter (#453)

* Added ruby mri linter

* Added to the list of supported linters

* Async and now with 4 spaces

* Vader tests for ruby

* Match style choices

* Vader test for the Ruby handler now works and passes

3 files changed, 80 insertions, 1 deletions

diff --git a/README.md b/README.md
index 7c0507ab..81793099 100644
--- a/README.md
+++ b/README.md
@@ -94,7 +94,7 @@ name. That seems to be the fairest way to arrange this table.
 | Puppet | [puppet](https://puppet.com), [puppet-lint](https://puppet-lint.com) |
 | Python | [flake8](http://flake8.pycqa.org/en/latest/), [mypy](http://mypy-lang.org/), [pylint](https://www.pylint.org/) |
 | reStructuredText | [proselint](http://proselint.com/)|
-| Ruby | [rubocop](https://github.com/bbatsov/rubocop) |
+| Ruby | [rubocop](https://github.com/bbatsov/rubocop), [ruby](https://www.ruby-lang.org) |
 | Rust | [rustc](https://www.rust-lang.org/), cargo (see `:help ale-integration-rust` for configuration instructions) |
 | SASS | [sass-lint](https://www.npmjs.com/package/sass-lint), [stylelint](https://github.com/stylelint/stylelint) |
 | SCSS | [sass-lint](https://www.npmjs.com/package/sass-lint), [scss-lint](https://github.com/brigade/scss-lint), [stylelint](https://github.com/stylelint/stylelint) |
diff --git a/ale_linters/ruby/ruby.vim b/ale_linters/ruby/ruby.vim
new file mode 100644
index 00000000..7cffcf3a
--- /dev/null
+++ b/ale_linters/ruby/ruby.vim
@@ -0,0 +1,40 @@
+" Author: Brandon Roehl - https://github.com/BrandonRoehl
+" Description: Ruby MRI for Ruby files
+
+function! ale_linters#ruby#ruby#Handle(buffer, lines) abort
+    " Matches patterns line the following:
+    "
+    " test.rb:3: warning: parentheses after method name is interpreted as an argument list, not a decomposed argument
+    " test.rb:8: syntax error, unexpected keyword_end, expecting end-of-input
+    let l:pattern = '\v^.+:(\d+): (warning: )?(.+)$'
+    let l:column = '\v^(\s+)\^$'
+    let l:output = []
+
+    for l:line in a:lines
+        let l:match = matchlist(l:line, l:pattern)
+        if len(l:match) == 0
+            let l:match = matchlist(l:line, l:column)
+            if len(l:match) != 0
+                let l:output[len(l:output) - 1]['col'] = len(l:match[1])
+            endif
+        else
+            call add(l:output, {
+            \   'bufnr': a:buffer,
+            \   'lnum': l:match[1] + 0,
+            \   'col': 0,
+            \   'text': l:match[2] . l:match[3],
+            \   'type': empty(l:match[2]) ? 'E' : 'W',
+            \})
+        endif
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('ruby', {
+\   'name': 'ruby',
+\   'executable': 'ruby',
+\   'output_stream': 'stderr',
+\   'command': 'ruby -w -c -T1 %t',
+\   'callback': 'ale_linters#ruby#ruby#Handle',
+\})
diff --git a/test/handler/test_ruby_handler.vader b/test/handler/test_ruby_handler.vader
new file mode 100644
index 00000000..573711f7
--- /dev/null
+++ b/test/handler/test_ruby_handler.vader
@@ -0,0 +1,39 @@
+Execute(The ruby handler should parse lines correctly and add the column if it can):
+  runtime ale_linters/ruby/ruby.vim
+  " Point Error
+  " Warning
+  " Line Error
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 6,
+  \     'bufnr': 255,
+  \     'col': 13,
+  \     'type': 'E',
+  \     'text': 'syntax error, unexpected '';'''
+  \   },
+  \   {
+  \     'lnum': 9,
+  \     'bufnr': 255,
+  \     'col': 0,
+  \     'type': 'W',
+  \     'text': 'warning: statement not reached'
+  \   },
+  \   {
+  \     'lnum': 12,
+  \     'bufnr': 255,
+  \     'col': 0,
+  \     'type': 'E',
+  \     'text': 'syntax error, unexpected end-of-input, expecting keyword_end'
+  \   }
+  \ ],
+  \ ale_linters#ruby#ruby#Handle(255, [
+  \ "test.rb:6: syntax error, unexpected ';'",
+  \ "        t = ;",
+  \ "             ^",
+  \ "test.rb:9: warning: statement not reached",
+  \ "test.rb:12: syntax error, unexpected end-of-input, expecting keyword_end",
+  \ ])
+
+After:
+  call ale#linter#Reset()