Fix #757 - Show :ALEDetail messages in a window

autoload/ale/cursor.vim

@@ -125,9 +125,7 @@ function! ale#cursor#ShowCursorDetail() abort
     if !empty(l:loc)
         let l:message = get(l:loc, 'detail', l:loc.text)
 
-        call s:EchoWithShortMess('off', l:message)
-
-        " Set the echo marker, so we can clear it by moving the cursor.
-        let l:info.echoed = 1
+        call ale#preview#Show(split(l:message, "\n"))
+        echo
     endif
 endfunction

autoload/ale/preview.vim

@@ -0,0 +1,18 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: Preview windows for showing whatever information in.
+
+" Open a preview window and show some lines in it.
+function! ale#preview#Show(lines) abort
+    silent pedit ALEPreviewWindow
+    wincmd P
+    setlocal modifiable
+    setlocal noreadonly
+    setlocal nobuflisted
+    setlocal filetype=ale-preview
+    setlocal buftype=nofile
+    setlocal bufhidden=wipe
+    :%d
+    call setline(1, a:lines)
+    setlocal nomodifiable
+    setlocal readonly
+endfunction

ftplugin/ale-preview.vim

@@ -0,0 +1,2 @@
+" Close the ALEPreviewWindow window with the q key.
+noremap <buffer> q :q!<CR>

test/test_cursor_warnings.vader

@@ -97,6 +97,11 @@ After:
   " carried over between test cases.
   echomsg ''
 
+  " Close the preview window if it's open.
+  if &filetype is# 'ale-preview'
+    noautocmd :q!
+  endif
+
 Given javascript(A Javscript file with warnings/errors):
   var x = 3 + 12345678
   var x = 5*2 + parseInt("10");
@@ -138,20 +143,21 @@ Execute(The message at the cursor should be shown on InsertLeave):
 Execute(ALEDetail should print 'detail' attributes):
   call cursor(1, 1)
 
-  redir => g:output
-    ALEDetail
-  redir END
+  ALEDetail
 
-  AssertEqual "\nEvery statement should end with a semicolon\nsecond line", g:output
+  AssertEqual
+  \ ['Every statement should end with a semicolon', 'second line'],
+  \ getline(1, '$')
 
 Execute(ALEDetail should print regular 'text' attributes):
   call cursor(2, 10)
 
-  redir => g:output
-    ALEDetail
-  redir END
+  ALEDetail
 
-  AssertEqual "\nInfix operators must be spaced.", g:output
+  " ALEDetail opens a window, so check the text in it.
+  AssertEqual
+  \ ['Infix operators must be spaced.'],
+  \ getline(1, '$')
 
 Execute(ALEDetail should not capitlise cursor messages):
   call cursor(3, 1)