diagnostics: support sending ALE output to Neovim's diagnostics API (#4345)

Support replacing ALE's display of problems with sending problems to the Neovim diagnostics API.

:help g:ale_use_neovim_diagnostics_api

Co-authored-by: David Balatero <dbalatero@users.noreply.github.com>
Co-authored-by: Georgi Angelchev <angelchev@live.co.uk>
Co-authored-by: w0rp <devw0rp@gmail.com>

test/sign/test_linting_sets_signs.vader

@@ -11,6 +11,7 @@ Before:
   Save g:ale_set_quickfix
   Save g:ale_set_signs
   Save g:ale_command_wrapper
+  Save g:ale_use_neovim_diagnostics_api
 
   let g:ale_command_wrapper = ''
   let g:ale_buffer_info = {}
@@ -22,6 +23,7 @@ Before:
   let g:ale_set_loclist = 0
   let g:ale_set_highlights = 0
   let g:ale_echo_cursor = 0
+  let g:ale_use_neovim_diagnostics_api = 0
 
   call ale#sign#Clear()
 
@@ -74,3 +76,10 @@ Execute(The signs should be updated after linting is done):
   call ale#test#FlushJobs()
 
   AssertEqual [['1', 'ALEWarningSign'], ['2', 'ALEErrorSign']], CollectSigns()
+
+Execute(Signs should not be set when diagnostics API integration is enabled):
+  let g:ale_use_neovim_diagnostics_api = 1
+  ALELint
+  call ale#test#FlushJobs()
+
+  AssertEqual [], CollectSigns()

test/test_ale_info.vader

@@ -52,6 +52,7 @@ Before:
   Save g:ale_sign_highlight_linenrs
   Save g:ale_statusline_format
   Save g:ale_type_map
+  Save g:ale_use_neovim_diagnostics_api
   Save g:ale_use_global_executables
   Save g:ale_virtualtext_cursor
   Save g:ale_warn_about_trailing_blank_lines
@@ -110,6 +111,7 @@ Before:
   let g:ale_sign_highlight_linenrs = 0
   let g:ale_statusline_format = ['%d error(s)', '%d warning(s)', 'OK']
   let g:ale_type_map = {}
+  let g:ale_use_neovim_diagnostics_api = 0
   let g:ale_use_global_executables = v:null
   let g:ale_virtualtext_cursor = 'disabled'
   let g:ale_warn_about_trailing_blank_lines = 1
@@ -189,6 +191,7 @@ Before:
   \  'let g:ale_sign_highlight_linenrs = 0',
   \  'let g:ale_statusline_format = [''%d error(s)'', ''%d warning(s)'', ''OK'']',
   \  'let g:ale_type_map = {}',
+  \  'let g:ale_use_neovim_diagnostics_api = 0',
   \  'let g:ale_use_global_executables = v:null',
   \  'let g:ale_virtualtext_cursor = ''disabled''',
   \  'let g:ale_warn_about_trailing_blank_lines = 1',

test/test_virtualtext.vader

@@ -4,6 +4,7 @@ Before:
   Save g:ale_virtualtext_delay
   Save g:ale_virtualtext_prefix
   Save b:ale_virtualtext_prefix
+  Save g:ale_use_neovim_diagnostics_api
 
   call ale#virtualtext#ResetDataForTests()
 
@@ -36,6 +37,7 @@ Before:
   \   ],
   \ },
   \}
+  let g:ale_use_neovim_diagnostics_api = 0
 
 After:
   Restore
@@ -177,3 +179,16 @@ Execute(We should set errors across all lines):
       \ map(prop_list(2), {_, v -> v.type})
     endif
   endif
+
+Execute(We should not set cursor messages when Neovim diagnostics are enabled):
+  let g:ale_use_neovim_diagnostics_api = 1
+
+  if has('patch-9.0.0297') || has('nvim-0.8.0')
+    let g:ale_virtualtext_cursor = 'current'
+    call cursor(1, 1)
+    call ale#virtualtext#ShowCursorWarningWithDelay()
+    " Tick the timer.
+    sleep 1ms
+
+    AssertEqual '', ale#virtualtext#GetLastMessageForTests()
+  endif