support running solargraph via bundle

ale_linters/ruby/solargraph.vim

@@ -8,7 +8,10 @@ call ale#Set('ruby_solargraph_executable', 'solargraph')
 call ale#Set('ruby_solargraph_options', {})
 
 function! ale_linters#ruby#solargraph#GetCommand(buffer) abort
-    return '%e' . ale#Pad('stdio')
+    let l:executable = ale#Var(a:buffer, 'ruby_solargraph_executable')
+
+    return ale#ruby#EscapeExecutable(l:executable, 'solargraph')
+    \   . ale#Pad('stdio')
 endfunction
 
 call ale#linter#Define('ruby', {

doc/ale-ruby.txt

@@ -227,8 +227,8 @@ g:ale_ruby_solargraph_executable
   Type: |String|
   Default: `'solargraph'`
 
-  Override the invoked solargraph binary. This is useful for running solargraph
-  from binstubs or a bundle.
+  Override the invoked solargraph binary. Set this to `'bundle'` to invoke
+  `'bundle` `exec` solargraph'.
 
 
 ===============================================================================

test/linter/test_ruby_solargraph.vader

@@ -13,6 +13,13 @@ Execute(command callback executable can be overridden):
   let g:ale_ruby_solargraph_executable = 'foobar'
   AssertLinter 'foobar', ale#Escape('foobar') . ' stdio'
 
+Execute(Setting bundle appends 'exec solargraph'):
+  let g:ale_ruby_solargraph_executable = 'path to/bundle'
+
+  AssertLinter 'path to/bundle', ale#Escape('path to/bundle')
+  \   . ' exec solargraph'
+  \   . ' stdio'
+
 Execute(should set solargraph for rails app):
   call ale#test#SetFilename('../test-files/ruby/valid_rails_app/app/models/thing.rb')
   AssertLSPLanguage 'ruby'