[eruby] Add GetCommand to erb linter

GetCommand conditionally adds a filter (implemented as inline Ruby code
in the command line) to transform some of the problematic
Rails-specific eRuby syntax. Specifically, <%= tags are replaced with
<%.

This does not reduce the effectiveness of the linter, because the
transformed code is still evaluated.

This solution was suggested by @rgo at
https://github.com/w0rp/ale/issues/580#issuecomment-337676607.

1 files changed, 17 insertions, 3 deletions

diff --git a/ale_linters/eruby/erb.vim b/ale_linters/eruby/erb.vim
index 18f92b3b..5d0b4003 100644
--- a/ale_linters/eruby/erb.vim
+++ b/ale_linters/eruby/erb.vim
@@ -1,11 +1,25 @@
-" Author: Matthias Guenther - https://wikimatze.de
+" Author: Matthias Guenther - https://wikimatze.de, Eddie Lebow https://github.com/elebow
 " Description: ERB from the Ruby standard library, for eruby/erb files
 
+function! ale_linters#eruby#erb#GetCommand(buffer) abort
+    let l:rails_root = ale#ruby#FindRailsRoot(a:buffer)
+
+    if empty(l:rails_root)
+        return 'erb -P -x %t | ruby -c'
+    endif
+
+    " Rails-flavored eRuby does not comply with the standard as understood by
+    " ERB, 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 erb -e ' . ale#Escape('puts ERB.new($stdin.read.gsub(%{<%=},%{<%}), nil, %{-}).src') . ' | ruby -c'
+endfunction
+
 call ale#linter#Define('eruby', {
 \   'name': 'erb',
+\   'aliases': ['erubylint'],
 \   'executable': 'erb',
-\    'output_stream': 'stderr',
-\   'command': 'erb -P -x %t | ruby -c',
+\   'output_stream': 'stderr',
+\   'command_callback': 'ale_linters#eruby#erb#GetCommand',
 \   'callback': 'ale#handlers#ruby#HandleSyntaxErrors',
 \})