diff --git a/autoload/ale.vim b/autoload/ale.vim
index dddb41db..f6c23d72 100644
--- a/autoload/ale.vim
+++ b/autoload/ale.vim
@@ -94,6 +94,11 @@ function! s:Lint(buffer, should_lint_file, timer_id) abort
     \   ? ale#engine#ignore#Exclude(l:filetype, l:linters, l:ignore_config)
     \   : l:linters
 
+    " Tell other sources that they can start checking the buffer now.
+    let g:ale_want_results_buffer = a:buffer
+    silent doautocmd <nomodeline> User ALEWantResults
+    unlet! g:ale_want_results_buffer
+
     " Don't set up buffer data and so on if there are no linters to run.
     if !has_key(g:ale_buffer_info, a:buffer) && empty(l:linters)
         return
diff --git a/autoload/ale/engine.vim b/autoload/ale/engine.vim
index 05db0e49..e85e4d66 100644
--- a/autoload/ale/engine.vim
+++ b/autoload/ale/engine.vim
@@ -79,6 +79,7 @@ function! ale#engine#InitBufferInfo(buffer) abort
         let g:ale_buffer_info[a:buffer] = {
         \   'job_list': [],
         \   'active_linter_list': [],
+        \   'active_other_sources_list': [],
         \   'loclist': [],
         \   'temporary_file_list': [],
         \   'temporary_directory_list': [],
@@ -97,6 +98,7 @@ function! ale#engine#IsCheckingBuffer(buffer) abort
     let l:info = get(g:ale_buffer_info, a:buffer, {})
 
     return !empty(get(l:info, 'active_linter_list', []))
+    \   || !empty(get(l:info, 'active_other_sources_list', []))
 endfunction
 
 " Register a temporary file to be managed with the ALE engine for
@@ -177,20 +179,27 @@ function! s:GatherOutput(job_id, line) abort
     endif
 endfunction
 
-function! ale#engine#HandleLoclist(linter_name, buffer, loclist) abort
+function! ale#engine#HandleLoclist(linter_name, buffer, loclist, from_other_source) abort
     let l:info = get(g:ale_buffer_info, a:buffer, {})
 
     if empty(l:info)
         return
     endif
 
-    " Remove this linter from the list of active linters.
-    " This may have already been done when the job exits.
-    call filter(l:info.active_linter_list, 'v:val isnot# a:linter_name')
+    if !a:from_other_source
+        " Remove this linter from the list of active linters.
+        " This may have already been done when the job exits.
+        call filter(l:info.active_linter_list, 'v:val isnot# a:linter_name')
+    endif
 
     " Make some adjustments to the loclists to fix common problems, and also
     " to set default values for loclist items.
-    let l:linter_loclist = ale#engine#FixLocList(a:buffer, a:linter_name, a:loclist)
+    let l:linter_loclist = ale#engine#FixLocList(
+    \   a:buffer,
+    \   a:linter_name,
+    \   a:from_other_source,
+    \   a:loclist,
+    \)
 
     " Remove previous items for this linter.
     call filter(l:info.loclist, 'v:val.linter_name isnot# a:linter_name')
@@ -263,7 +272,7 @@ function! s:HandleExit(job_id, exit_code) abort
         let l:loclist = []
     endtry
 
-    call ale#engine#HandleLoclist(l:linter.name, l:buffer, l:loclist)
+    call ale#engine#HandleLoclist(l:linter.name, l:buffer, l:loclist, 0)
 endfunction
 
 function! ale#engine#SetResults(buffer, loclist) abort
@@ -335,7 +344,7 @@ function! s:RemapItemTypes(type_map, loclist) abort
     endfor
 endfunction
 
-function! ale#engine#FixLocList(buffer, linter_name, loclist) abort
+function! ale#engine#FixLocList(buffer, linter_name, from_other_source, loclist) abort
     let l:bufnr_map = {}
     let l:new_loclist = []
 
@@ -368,6 +377,10 @@ function! ale#engine#FixLocList(buffer, linter_name, loclist) abort
         \   'linter_name': a:linter_name,
         \}
 
+        if a:from_other_source
+            let l:item.from_other_source = 1
+        endif
+
         if has_key(l:old_item, 'code')
             let l:item.code = l:old_item.code
         endif
@@ -691,6 +704,7 @@ endfunction
 function! s:RemoveProblemsForDisabledLinters(buffer, linters) abort
     " Figure out which linters are still enabled, and remove
     " problems for linters which are no longer enabled.
+    " Problems from other sources will be kept.
     let l:name_map = {}
 
     for l:linter in a:linters
@@ -699,7 +713,7 @@ function! s:RemoveProblemsForDisabledLinters(buffer, linters) abort
 
     call filter(
     \   get(g:ale_buffer_info[a:buffer], 'loclist', []),
-    \   'get(l:name_map, get(v:val, ''linter_name''))',
+    \   'get(v:val, ''from_other_source'') || get(l:name_map, get(v:val, ''linter_name''))',
     \)
 endfunction
 
diff --git a/autoload/ale/lsp/reset.vim b/autoload/ale/lsp/reset.vim
index c7c97a47..2fc7f0a2 100644
--- a/autoload/ale/lsp/reset.vim
+++ b/autoload/ale/lsp/reset.vim
@@ -17,7 +17,7 @@ function! ale#lsp#reset#StopAllLSPs() abort
 
             for l:linter in ale#linter#Get(getbufvar(l:buffer, '&filetype'))
                 if !empty(l:linter.lsp)
-                    call ale#engine#HandleLoclist(l:linter.name, l:buffer, [])
+                    call ale#engine#HandleLoclist(l:linter.name, l:buffer, [], 0)
                 endif
             endfor
         endfor
diff --git a/autoload/ale/lsp_linter.vim b/autoload/ale/lsp_linter.vim
index 55190483..fa4d2f86 100644
--- a/autoload/ale/lsp_linter.vim
+++ b/autoload/ale/lsp_linter.vim
@@ -38,7 +38,7 @@ function! s:HandleLSPDiagnostics(conn_id, response) abort
 
     let l:loclist = ale#lsp#response#ReadDiagnostics(a:response)
 
-    call ale#engine#HandleLoclist(l:linter_name, l:buffer, l:loclist)
+    call ale#engine#HandleLoclist(l:linter_name, l:buffer, l:loclist, 0)
 endfunction
 
 function! s:HandleTSServerDiagnostics(response, error_type) abort
@@ -81,7 +81,7 @@ function! s:HandleTSServerDiagnostics(response, error_type) abort
     let l:loclist = get(l:info, 'semantic_loclist', [])
     \   + get(l:info, 'syntax_loclist', [])
 
-    call ale#engine#HandleLoclist(l:linter_name, l:buffer, l:loclist)
+    call ale#engine#HandleLoclist(l:linter_name, l:buffer, l:loclist, 0)
 endfunction
 
 function! s:HandleLSPErrorMessage(linter_name, response) abort
diff --git a/autoload/ale/other_source.vim b/autoload/ale/other_source.vim
new file mode 100644
index 00000000..1a092034
--- /dev/null
+++ b/autoload/ale/other_source.vim
@@ -0,0 +1,21 @@
+" Tell ALE that another source has started checking a buffer.
+function! ale#other_source#StartChecking(buffer, linter_name) abort
+    call ale#engine#InitBufferInfo(a:buffer)
+    let l:list = g:ale_buffer_info[a:buffer].active_other_sources_list
+
+    call add(l:list, a:linter_name)
+    call uniq(sort(l:list))
+endfunction
+
+" Show some results, and stop checking a buffer.
+" To clear results or cancel checking a buffer, an empty List can be given.
+function! ale#other_source#ShowResults(buffer, linter_name, loclist) abort
+    call ale#engine#InitBufferInfo(a:buffer)
+    let l:info = g:ale_buffer_info[a:buffer]
+
+    " Remove this linter name from the active list.
+    let l:list = l:info.active_other_sources_list
+    call filter(l:list, 'v:val isnot# a:linter_name')
+
+    call ale#engine#HandleLoclist(a:linter_name, a:buffer, a:loclist, 1)
+endfunction
diff --git a/doc/ale.txt b/doc/ale.txt
index e190cf2a..2a8f17d4 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -9,6 +9,7 @@ CONTENTS                                                         *ale-contents*
   1. Introduction.........................|ale-introduction|
   2. Supported Languages & Tools..........|ale-support|
   3. Linting..............................|ale-lint|
+    3.1 Other Sources.....................|ale-lint-other-sources|
   4. Fixing Problems......................|ale-fix|
   5. Language Server Protocol Support.....|ale-lsp|
     5.1 Completion........................|ale-completion|
@@ -574,6 +575,68 @@ ALE offers several options for controlling which linters are run.
 * Only running linters you asked for.  - |g:ale_linters_explicit|
 
 
+-------------------------------------------------------------------------------
+3.1 Other Sources                                      *ale-lint-other-sources*
+
+Problems for a buffer can be taken from other sources and rendered by ALE.
+This allows ALE to be used in combination with other plugins which also want
+to display any problems they might find with a buffer. ALE's API includes the
+following components for making this possible.
+
+* |ale#other_source#StartChecking()| - Tell ALE that a buffer is being checked.
+* |ale#other_source#ShowResults()|   - Show results from another source.
+* |ALEWantResults|                   - A signal for when ALE wants results.
+
+Other resources can provide results for ALE to display at any time, following
+ALE's loclist format. (See |ale-loclist-format|) For example: >
+
+  " Tell ALE to show some results.
+  " This function can be called at any time.
+  call ale#other_source#ShowResults(bufnr(''), 'some-linter-name', [
+  \ {'text': 'Something went wrong', lnum: 13},
+  \])
+<
+
+Other sources should use a unique name for identifying themselves. A single
+linter name can be used for all problems from another source, or a series of
+unique linter names can be used. Results can be cleared for that source by
+providing an empty List.
+
+|ale#other_source#StartChecking()| should be called whenever another source
+starts checking a buffer, so other tools can know that a buffer is being
+checked by some plugin. The |ALEWantResults| autocmd event can be used to
+start checking a buffer for problems every time that ALE does. When
+|ALEWantResults| is signaled, |g:ale_want_results_buffer| will be set to the
+number of the buffer that ALE wants to check.
+|ale#other_source#StartChecking()| should be called synchronously, and other
+sources should perform their checks on a buffer in the background
+asynchronously, so they don't interrupt editing.
+
+A plugin might integrate its own checks with ALE like so: >
+
+  augroup SomeGroupName
+    autocmd!
+    autocmd User ALEWantResults call Hook(g:ale_want_results_buffer)
+  augroup END
+
+  function! DoBackgroundWork(buffer) abort
+    " Start some work in the background here.
+    " ...
+    " Then call WorkDone(a:buffer, results)
+  endfunction
+
+  function! Hook(buffer) abort
+    " Tell ALE we're going to check this buffer.
+    call ale#other_source#StartChecking(a:buffer, 'some-name')
+    call DoBackgroundWork(a:buffer)
+  endfunction
+
+  function! WorkDone(buffer, results) abort
+    " Send results to ALE after they have been collected.
+    call ale#other_source#ShowResults(buffer, 'some-name', a:results)
+  endfunction
+<
+
 ===============================================================================
 4. Fixing Problems                                                    *ale-fix*
 
@@ -2763,6 +2826,25 @@ ale#linter#PreventLoading(filetype)               *ale#linter#PreventLoading()*
   |runtimepath| for that filetype. This function can be called from vimrc or
   similar to prevent ALE from loading linters.
 
+ale#other_source#ShowResults(buffer, linter_name, loclist)
+                                               *ale#other_source#ShowResults()*
+
+  Show results from another source of information.
+
+  `buffer` must be a valid buffer number, and `linter_name` must be a unique
+  name for identifying another source of information. The `loclist` given
+  where the problems in a buffer are, and should be provided in the format ALE
+  uses for regular linter results. See |ale-loclist-format|.
+
+
+ale#other_source#StartChecking(buffer, linter_name)
+                                             *ale#other_source#StartChecking()*
+
+  Tell ALE that another source of information has started checking a buffer.
+
+  `buffer` must be a valid buffer number, and `linter_name` must be a unique
+  name for identifying another source of information.
+
 
 ale#statusline#Count(buffer)                           *ale#statusline#Count()*
 
@@ -2791,10 +2873,21 @@ b:ale_linted                                                     *b:ale_linted*
     echo getbufvar(bufnr(''), 'ale_linted', 0) > 0 ? 'checked' : 'not checked'
 <
 
+g:ale_want_results_buffer                           *g:ale_want_results_buffer*
+
+  `g:ale_want_results_buffer` is set to the number of the buffer being checked
+  when the |ALEWantResults| event is signaled. This variable should be read to
+  figure out which buffer other sources should lint.
+
+
 ALELintPre                                                 *ALELintPre-autocmd*
+                                                                   *ALELintPre*
 ALELintPost                                               *ALELintPost-autocmd*
+                                                                  *ALELintPost*
 ALEFixPre                                                   *ALEFixPre-autocmd*
+                                                                    *ALEFixPre*
 ALEFixPost                                                 *ALEFixPost-autocmd*
+                                                                   *ALEFixPost*
 
   These |User| autocommands are triggered before and after every lint or fix
   cycle. They can be used to update statuslines, send notifications, etc.
@@ -2808,7 +2901,7 @@ ALEFixPost                                                 *ALEFixPost-autocmd*
         autocmd!
         autocmd User ALELintPre  hi Statusline ctermfg=darkgrey
         autocmd User ALELintPost hi Statusline ctermfg=NONE
-    augroup end
+    augroup END
 <
   Or to display the progress in the statusline:
 >
@@ -2818,10 +2911,11 @@ ALEFixPost                                                 *ALEFixPost-autocmd*
         autocmd!
         autocmd User ALELintPre  let s:ale_running = 1 | redrawstatus
         autocmd User ALELintPost let s:ale_running = 0 | redrawstatus
-    augroup end
+    augroup END
 
 <
 ALEJobStarted                                           *ALEJobStarted-autocmd*
+                                                                *ALEJobStarted*
 
   This |User| autocommand is triggered immediately after a job is successfully
   run. This provides better accuracy for checking linter status with
@@ -2829,6 +2923,22 @@ ALEJobStarted                                           *ALEJobStarted-autocmd*
   triggered before any linters are executed.
 
 
+ALEWantResults                                         *ALEWantResults-autocmd*
+                                                               *ALEWantResults*
+
+  This |User| autocommand is triggered before ALE begins a lint cycle. Another
+  source can respond by calling |ale#other_source#StartChecking()|, and
+  |ALELintPre| will be signaled thereafter, to allow other plugins to know
+  that another source is checking the buffer.
+
+  |g:ale_want_results_buffer| will be set to the number for a buffer being
+  checked when the event is signaled, and deleted after the event is done.
+  This variable should be read to know which buffer to check.
+
+  Other plugins can use this event to start checking buffers when ALE events
+  for checking buffers are triggered.
+
+
 ===============================================================================
 10. Special Thanks                                         *ale-special-thanks*
 
diff --git a/test/fix/test_ale_fix.vader b/test/fix/test_ale_fix.vader
index 67b8b212..539972a4 100644
--- a/test/fix/test_ale_fix.vader
+++ b/test/fix/test_ale_fix.vader
@@ -23,7 +23,7 @@ Before:
     autocmd!
     autocmd User ALEFixPre let g:pre_success = 1
     autocmd User ALEFixPost let g:post_success = 1
-  augroup end
+  augroup END
 
   if !has('win32')
     let &shell = '/bin/bash'
@@ -180,7 +180,6 @@ After:
   unlet! g:ale_emulate_job_failure
   unlet! b:ale_fixers
   unlet! b:ale_fix_on_save
-  augroup! VaderTest
   delfunction AddCarets
   delfunction AddDollars
   delfunction DoNothing
@@ -204,6 +203,12 @@ After:
   delfunction FixWithJSONPostProcessing
   delfunction JSONPostProcessor
 
+  augroup VaderTest
+    autocmd!
+  augroup END
+
+  augroup! VaderTest
+
   call ale#test#RestoreDirectory()
 
   call ale#fix#registry#ResetToDefaults()
diff --git a/test/test_alejobstarted_autocmd.vader b/test/test_alejobstarted_autocmd.vader
index 388e5439..6fa1ff8e 100644
--- a/test/test_alejobstarted_autocmd.vader
+++ b/test/test_alejobstarted_autocmd.vader
@@ -23,10 +23,11 @@ After:
 
   let g:ale_run_synchronously = 0
 
-  try
-    augroup! VaderTest
-  catch
-  endtry
+  augroup VaderTest
+    autocmd!
+  augroup END
+
+  augroup! VaderTest
 
   unlet! g:job_started_success
 
@@ -38,7 +39,7 @@ Execute(Run a lint cycle with an actual job to check for ALEJobStarted):
   augroup VaderTest
     autocmd!
     autocmd User ALEJobStarted let g:job_started_success = 1
-  augroup end
+  augroup END
 
   ALELint
 
diff --git a/test/test_alelint_autocmd.vader b/test/test_alelint_autocmd.vader
index 9a7a6a43..332cb36f 100644
--- a/test/test_alelint_autocmd.vader
+++ b/test/test_alelint_autocmd.vader
@@ -9,10 +9,11 @@ After:
   let g:ale_run_synchronously = 0
   let g:ale_buffer_info = {}
 
-  try
-    augroup! VaderTest
-  catch
-  endtry
+  augroup VaderTest
+    autocmd!
+  augroup END
+
+  augroup! VaderTest
 
 Given testft(An empty file):
 Execute(Run a lint cycle, and check that a variable is set in the autocmd):
@@ -20,7 +21,7 @@ Execute(Run a lint cycle, and check that a variable is set in the autocmd):
     autocmd!
     autocmd User ALELintPre let g:pre_success = 1
     autocmd User ALELintPost let g:post_success = 1
-  augroup end
+  augroup END
 
   call ale#Queue(0)
 
diff --git a/test/test_checkingbuffer_autocmd.vader b/test/test_checkingbuffer_autocmd.vader
index 9e3a8188..9e642b15 100644
--- a/test/test_checkingbuffer_autocmd.vader
+++ b/test/test_checkingbuffer_autocmd.vader
@@ -31,7 +31,7 @@ After:
 
   augroup VaderTest
     autocmd!
-  augroup end
+  augroup END
 
   augroup! VaderTest
 
@@ -40,7 +40,7 @@ Execute(ALELintPre should not return success on ale#engine#IsCheckingBuffer):
   augroup VaderTest
     autocmd!
     autocmd User ALELintPre let g:checking_buffer = ale#engine#IsCheckingBuffer(bufnr('')) ? 1 : 0
-  augroup end
+  augroup END
 
   ALELint
 
@@ -50,7 +50,7 @@ Execute(ALEJobStarted should return success on ale#engine#IsCheckingBuffer):
   augroup VaderTest
     autocmd!
     autocmd User ALEJobStarted let g:checking_buffer = ale#engine#IsCheckingBuffer(bufnr('')) ? 1 : 0
-  augroup end
+  augroup END
 
   ALELint
 
diff --git a/test/test_ignoring_linters.vader b/test/test_ignoring_linters.vader
index f47c5e81..866f9e0d 100644
--- a/test/test_ignoring_linters.vader
+++ b/test/test_ignoring_linters.vader
@@ -108,7 +108,7 @@ Before:
     let g:run_linters_called = 1
   endfunction
 
-  function! ale#engine#HandleLoclist(linter_name, buffer, loclist) abort
+  function! ale#engine#HandleLoclist(linter_name, buffer, loclist, from_other_source) abort
     let g:loclist = a:loclist
   endfunction
 
diff --git a/test/test_linter_type_mapping.vader b/test/test_linter_type_mapping.vader
index 0131b5f0..0ec22a56 100644
--- a/test/test_linter_type_mapping.vader
+++ b/test/test_linter_type_mapping.vader
@@ -16,7 +16,7 @@ Execute(It should be possible to remap errors to style errors):
   \   {'type': 'W', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'I', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
@@ -35,7 +35,7 @@ Execute(It should be possible to remap errors to style errors with buffer-local
   \   {'type': 'W', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'I', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
@@ -54,7 +54,7 @@ Execute(It should be possible to remap warnings to style warnings):
   \   {'type': 'W', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'I', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
@@ -73,7 +73,7 @@ Execute(It should be possible to remap style errors to errors):
   \   {'type': 'W', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'I', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
@@ -92,7 +92,7 @@ Execute(It should be possible to remap style warnings to warnings):
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'I', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
@@ -111,7 +111,7 @@ Execute(It should be possible to info problems to warnings):
   \   {'type': 'W', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1, 'linter_name': 'foo'},
   \ ],
-  \ ale#engine#FixLocList(bufnr(''), 'foo', [
+  \ ale#engine#FixLocList(bufnr(''), 'foo', 0, [
   \   {'type': 'E', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'E', 'sub_type': 'style', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
   \   {'type': 'W', 'lnum': 1, 'text': 'x', 'bufnr': bufnr(''), 'col': 0, 'vcol': 0, 'nr': -1},
diff --git a/test/test_loclist_corrections.vader b/test/test_loclist_corrections.vader
index 48aa1f78..343620a5 100644
--- a/test/test_loclist_corrections.vader
+++ b/test/test_loclist_corrections.vader
@@ -41,6 +41,7 @@ Execute(FixLocList should set all the default values correctly):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': 2}, {'text': 'b', 'lnum': 2}],
   \ )
 
@@ -61,6 +62,7 @@ Execute(FixLocList should use the values we supply):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{
   \     'text': 'a',
   \     'lnum': 3,
@@ -89,6 +91,7 @@ Execute(FixLocList should set items with lines beyond the end to the last line):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': 11}],
   \ )
 
@@ -109,6 +112,7 @@ Execute(FixLocList should move line 0 to line 1):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': 0}],
   \ )
 
@@ -130,6 +134,7 @@ Execute(FixLocList should convert line and column numbers correctly):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': '010', 'col': '010'}],
   \ )
 
@@ -163,6 +168,7 @@ Execute(FixLocList should pass on end_col values):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [
   \     {'text': 'a', 'lnum': '010', 'col': '010', 'end_col': '012'},
   \     {'text': 'a', 'lnum': '010', 'col': '011', 'end_col': 12},
@@ -200,6 +206,7 @@ Execute(FixLocList should pass on end_lnum values):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [
   \     {'text': 'a', 'lnum': '010', 'col': '010', 'end_col': '012', 'end_lnum': '013'},
   \     {'text': 'a', 'lnum': '010', 'col': '011', 'end_col': 12, 'end_lnum': 13},
@@ -224,6 +231,7 @@ Execute(FixLocList should allow subtypes to be set):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': 11, 'sub_type': 'style'}],
   \ )
 
@@ -285,6 +293,7 @@ Execute(FixLocList should accept filenames):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [
   \     {'text': 'a', 'lnum': 2, 'filename': expand('%:p')},
   \     {'text': 'a', 'lnum': 3, 'filename': expand('%:p')},
@@ -322,6 +331,7 @@ Execute(FixLocList should interpret temporary filenames as being the current buf
   \ ale#engine#FixLocList(
   \   bufnr(''),
   \   'foobar',
+  \   0,
   \   [
   \     {'text': 'a', 'lnum': 2, 'filename': b:temp_name},
   \     {'text': 'a', 'lnum': 3, 'filename': substitute(b:temp_name, '\\', '/', 'g')},
@@ -346,9 +356,43 @@ Execute(The error code should be passed on):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [{'text': 'a', 'lnum': 11, 'code': 'some-code'}],
   \ )
 
+Execute(FixLocList should mark problems as coming from other sources if requested):
+  AssertEqual
+  \ [
+  \   {
+  \     'text': 'a',
+  \     'lnum': 2,
+  \     'col': 0,
+  \     'bufnr': bufnr('%'),
+  \     'vcol': 0,
+  \     'type': 'E',
+  \     'nr': -1,
+  \     'linter_name': 'foobar',
+  \     'from_other_source': 1,
+  \   },
+  \   {
+  \     'text': 'b',
+  \     'lnum': 2,
+  \     'col': 0,
+  \     'bufnr': bufnr('%'),
+  \     'vcol': 0,
+  \     'type': 'E',
+  \     'nr': -1,
+  \     'linter_name': 'foobar',
+  \     'from_other_source': 1,
+  \   },
+  \],
+  \ ale#engine#FixLocList(
+  \   bufnr('%'),
+  \   'foobar',
+  \   1,
+  \   [{'text': 'a', 'lnum': 2}, {'text': 'b', 'lnum': 2}],
+  \ )
+
 Given(A file with Japanese multi-byte text):
   はじめまして!
   -私はワープです。
@@ -367,6 +411,7 @@ Execute(character positions should be converted to byte positions):
   \ ale#engine#FixLocList(
   \   bufnr('%'),
   \   'foobar',
+  \   0,
   \   [
   \     {'text': 'a', 'lnum': 1, 'col': 0, 'vcol': 1},
   \     {'text': 'a', 'lnum': 1, 'col': 1, 'vcol': 1},
diff --git a/test/test_other_sources.vader b/test/test_other_sources.vader
new file mode 100644
index 00000000..e6f9911c
--- /dev/null
+++ b/test/test_other_sources.vader
@@ -0,0 +1,153 @@
+Before:
+  Save g:ale_buffer_info
+  Save g:ale_set_signs
+  Save g:ale_set_quickfix
+  Save g:ale_set_loclist
+  Save g:ale_set_highlights
+  Save g:ale_echo_cursor
+
+  let g:ale_buffer_info = {}
+  let g:ale_run_synchronously = 1
+  let g:ale_set_lists_synchronously = 1
+  let g:ale_set_signs = 0
+  let g:ale_set_quickfix = 0
+  let g:ale_set_loclist = 1
+  let g:ale_set_highlights = 0
+  let g:ale_echo_cursor = 0
+
+  function! TestCallback(buffer, output)
+    return []
+  endfunction
+
+  call ale#linter#Define('foobar', {
+  \ 'name': 'testlinter',
+  \ 'callback': 'TestCallback',
+  \ 'executable': has('win32') ? 'cmd' : 'echo',
+  \ 'command': has('win32') ? 'echo foo bar' : '/bin/sh -c ''echo foo bar''',
+  \})
+
+After:
+  Restore
+
+  unlet! b:ale_linters
+  unlet! g:want_results_signaled
+  unlet! g:want_results_buffer_value
+  unlet! g:lint_pre_signaled
+  unlet! g:ale_run_synchronously
+  unlet! g:ale_set_lists_synchronously
+
+  delfunction TestCallback
+
+  augroup VaderTest
+    autocmd!
+  augroup END
+
+  augroup! VaderTest
+
+  call ale#linter#Reset()
+  call setloclist(0, [])
+
+Given foobar (Some imaginary filetype):
+Execute(StartChecking should mark a buffer as being actively checked):
+  Assert !ale#engine#IsCheckingBuffer(bufnr(''))
+
+  call ale#other_source#StartChecking(bufnr(''), 'other-source-linter')
+
+  Assert ale#engine#IsCheckingBuffer(bufnr(''))
+
+Execute(ShowResults sould make a buffer inactive):
+  call ale#other_source#StartChecking(bufnr(''), 'other-source-linter')
+  call ale#other_source#StartChecking(bufnr(''), 'second-other-source-linter')
+
+  call ale#other_source#ShowResults(bufnr(''), 'other-source-linter', [])
+
+  Assert ale#engine#IsCheckingBuffer(bufnr(''))
+
+  call ale#other_source#ShowResults(bufnr(''), 'second-other-source-linter', [])
+
+  Assert !ale#engine#IsCheckingBuffer(bufnr(''))
+
+Execute(ShowResults should show results at any time):
+  call ale#other_source#ShowResults(bufnr(''), 'other-source-linter', [
+  \ {'text': 'xyz', 'lnum': 1},
+  \])
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'bufnr': bufnr(''),
+  \     'col': 0,
+  \     'valid': 1,
+  \     'vcol': 0,
+  \     'nr': -1,
+  \     'type': 'E',
+  \     'pattern': '',
+  \     'text': 'xyz',
+  \   },
+  \ ],
+  \ ale#test#GetLoclistWithoutModule()
+
+  call ale#other_source#ShowResults(bufnr(''), 'other-source-linter', [])
+
+  AssertEqual [], ale#test#GetLoclistWithoutModule()
+
+Execute(A regular lint cycle shouldn't clear results from other sources):
+  call ale#other_source#ShowResults(bufnr(''), 'other-source-linter', [
+  \ {'text': 'xyz', 'lnum': 1},
+  \])
+  ALELint
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 1,
+  \     'bufnr': bufnr(''),
+  \     'col': 0,
+  \     'valid': 1,
+  \     'vcol': 0,
+  \     'nr': -1,
+  \     'type': 'E',
+  \     'pattern': '',
+  \     'text': 'xyz',
+  \   },
+  \ ],
+  \ ale#test#GetLoclistWithoutModule()
+
+Execute(ALEWantResults should be signaled when a buffer is checked):
+  augroup VaderTest
+    autocmd!
+    autocmd User ALEWantResults let g:want_results_signaled = 1
+    autocmd User ALELintPre let g:lint_pre_signaled = 1
+  augroup END
+
+  " Even when all linters are disabled, we should send the signal.
+  let b:ale_linters = []
+  ALELint
+
+  Assert get(g:, 'want_results_signaled')
+  Assert !get(g:, 'lint_pre_signaled')
+
+Execute(ALEWantResults should set a variable indicating which buffer is being checked):
+  augroup VaderTest
+    autocmd!
+    autocmd User ALEWantResults let g:want_results_buffer_value = g:ale_want_results_buffer
+  augroup END
+
+  let b:ale_linters = []
+  ALELint
+
+  AssertEqual bufnr(''), g:want_results_buffer_value
+
+Execute(ALEWantResults should lead to an ALELintPre signal if another source responds):
+  augroup VaderTest
+    autocmd!
+    autocmd User ALEWantResults call ale#other_source#StartChecking(bufnr(''), 'other-source-linter')
+    autocmd User ALELintPre let g:lint_pre_signaled = 1
+  augroup END
+
+  " Even when all linters are disabled, we should send the signal.
+  let b:ale_linters = []
+  ALELint
+
+  Assert get(g:, 'lint_pre_signaled')
diff --git a/test/test_redundant_tsserver_rendering_avoided.vader b/test/test_redundant_tsserver_rendering_avoided.vader
index 41cbe5e0..a292b014 100644
--- a/test/test_redundant_tsserver_rendering_avoided.vader
+++ b/test/test_redundant_tsserver_rendering_avoided.vader
@@ -45,7 +45,7 @@ Before:
   let g:ale_buffer_info = {bufnr(''): {'loclist': []}}
   let g:ale_handle_loclist_called = 0
 
-  function! ale#engine#HandleLoclist(linter_name, buffer, loclist) abort
+  function! ale#engine#HandleLoclist(linter_name, buffer, loclist, from_other_source) abort
     let g:ale_handle_loclist_called = 1
   endfunction
 
diff --git a/test/test_setting_problems_found_in_previous_buffers.vader b/test/test_setting_problems_found_in_previous_buffers.vader
index 4604005a..36eeb4ca 100644
--- a/test/test_setting_problems_found_in_previous_buffers.vader
+++ b/test/test_setting_problems_found_in_previous_buffers.vader
@@ -9,14 +9,14 @@ Before:
   let g:ale_buffer_info = {}
   call ale#engine#InitBufferInfo(bufnr('') + 1)
   let g:ale_buffer_info[bufnr('') + 1].loclist =
-  \ ale#engine#FixLocList(bufnr('') + 1, 'linter_one', [
+  \ ale#engine#FixLocList(bufnr('') + 1, 'linter_one', 0, [
   \   {'lnum': 1, 'filename': expand('%:p'), 'text': 'foo'},
   \   {'lnum': 2, 'filename': expand('%:p'), 'text': 'bar'},
   \   {'lnum': 2, 'text': 'ignore this one'},
   \ ])
   call ale#engine#InitBufferInfo(bufnr('') + 2)
   let g:ale_buffer_info[bufnr('') + 2].loclist =
-  \ ale#engine#FixLocList(bufnr('') + 2, 'linter_one', [
+  \ ale#engine#FixLocList(bufnr('') + 2, 'linter_one', 0, [
   \   {'lnum': 1, 'filename': expand('%:p'), 'text': 'foo'},
   \   {'lnum': 3, 'filename': expand('%:p'), 'text': 'baz'},
   \   {'lnum': 5, 'text': 'ignore this one'},