Fix #537 - Add support for balloons

autoload/ale/balloon.vim

@@ -0,0 +1,21 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: balloonexpr support for ALE.
+
+function! ale#balloon#MessageForPos(bufnr, lnum, col) abort
+    let l:loclist = get(g:ale_buffer_info, a:bufnr, {'loclist': []}).loclist
+    let l:index = ale#util#BinarySearch(l:loclist, a:lnum, a:col)
+
+    return l:index >= 0 ? l:loclist[l:index].text : ''
+endfunction
+
+function! ale#balloon#Expr() abort
+    return ale#balloon#MessageForPos(v:beval_bufnr, v:beval_lnum, v:beval_col)
+endfunction
+
+function! ale#balloon#Disable() abort
+    set noballooneval
+endfunction
+
+function! ale#balloon#Enable() abort
+    set ballooneval balloonexpr=ale#balloon#Expr()
+endfunction