[eruby] Add erubi linter

Erubi is yet another parser for eRuby. This is the default parser in
Rails as of version 5.1. It supports some additional syntax with similar
behavior to Rails' extensions to the language, though incompatible.
Rails currently still recommends their own syntax, so GetCommand still
has to do the translation introduced in
https://github.com/w0rp/ale/pull/1114 .

Erubi does not supply an executable—It is intended to be invoked only
from within a Ruby program. In this case, a one-liner on the command
line.

1 files changed, 35 insertions, 0 deletions

diff --git a/ale_linters/eruby/erubi.vim b/ale_linters/eruby/erubi.vim
new file mode 100644
index 00000000..6f2d3ac6
--- /dev/null
+++ b/ale_linters/eruby/erubi.vim
@@ -0,0 +1,35 @@
+" Author: Eddie Lebow https://github.com/elebow
+" Description: eruby checker using `erubi`
+
+function! ale_linters#eruby#erubi#CheckErubi(buffer) abort
+    return 'ruby -r erubi/capture_end -e ' . ale#Escape('""')
+endfunction
+
+function! ale_linters#eruby#erubi#GetCommand(buffer, check_erubi_output) abort
+    let l:rails_root = ale#ruby#FindRailsRoot(a:buffer)
+
+    if (!empty(a:check_erubi_output))
+        " The empty command in CheckErubi returns nothing if erubi runs and
+        " emits an error if erubi is not present
+        return ''
+    endif
+
+    if empty(l:rails_root)
+        return 'ruby -r erubi/capture_end -e ' . ale#Escape('puts Erubi::CaptureEndEngine.new($stdin.read).src') . '< %t | ruby -c'
+    endif
+
+    " Rails-flavored eRuby does not comply with the standard as understood by
+    " Erubi, so we'll have to do some substitution. This does not reduce the
+    " effectiveness of the linter---the translated code is still evaluated.
+    return 'ruby -r erubi/capture_end -e ' . ale#Escape('puts Erubi::CaptureEndEngine.new($stdin.read.gsub(%{<%=},%{<%}), nil, %{-}).src') . '< %t | ruby -c'
+endfunction
+
+call ale#linter#Define('eruby', {
+\   'name': 'erubi',
+\   'executable': 'ruby',
+\   'command_chain': [
+\     {'callback': 'ale_linters#eruby#erubi#CheckErubi'},
+\     {'callback': 'ale_linters#eruby#erubi#GetCommand', 'output_stream': 'stderr'},
+\   ],
+\   'callback': 'ale#handlers#ruby#HandleSyntaxErrors',
+\})