#2132 - Implement deferred command handling for linters

autoload/ale/assert.vim

@@ -59,13 +59,18 @@ function! ale#assert#Linter(expected_executable, expected_command) abort
         endif
     else
         let l:command = ale#linter#GetCommand(l:buffer, l:linter)
+
+        while ale#command#IsDeferred(l:command)
+            call ale#test#FlushJobs()
+            let l:command = l:command.value
+        endwhile
     endif
 
     if type(l:command) is v:t_string
         " Replace %e with the escaped executable, so tests keep passing after
         " linters are changed to use %e.
         let l:command = substitute(l:command, '%e', '\=ale#Escape(l:executable)', 'g')
-    else
+    elseif type(l:command) is v:t_list
         call map(l:command, 'substitute(v:val, ''%e'', ''\=ale#Escape(l:executable)'', ''g'')')
     endif
 

autoload/ale/command.vim

@@ -320,6 +320,10 @@ function! ale#command#Run(buffer, command, Callback, ...) abort
         call ale#history#Add(a:buffer, l:status, l:job_id, l:command)
     endif
 
+    if !l:job_id
+        return 0
+    endif
+
     " We'll return this Dictionary. A `result_callback` can be assigned to it
     " later for capturing the result of a:Callback.
     "

autoload/ale/engine.vim

@@ -422,8 +422,16 @@ endfunction
 
 " Run a job.
 "
-" Returns 1 when the job was started successfully.
+" Returns 1 when a job was started successfully.
 function! s:RunJob(command, options) abort
+    if ale#command#IsDeferred(a:command)
+        let a:command.result_callback = {
+        \   command -> s:RunJob(command, a:options)
+        \}
+
+        return 1
+    endif
+
     let l:command = a:command
 
     if empty(l:command)
@@ -451,7 +459,7 @@ function! s:RunJob(command, options) abort
     \})
 
     " Only proceed if the job is being run.
-    if !l:result._deferred_job_id
+    if empty(l:result)
         return 0
     endif
 

autoload/ale/fix.vim

@@ -179,7 +179,7 @@ function! s:RunJob(options) abort
     \   'log_output': 0,
     \})
 
-    return l:result._deferred_job_id != 0
+    return !empty(l:result)
 endfunction
 
 function! s:RunFixer(options) abort

autoload/ale/linter.vim

@@ -177,7 +177,8 @@ function! ale#linter#PreProcess(filetype, linter) abort
         let l:obj.command = a:linter.command
 
         if type(l:obj.command) isnot v:t_string
-            throw '`command` must be a string if defined'
+        \&& type(l:obj.command) isnot v:t_func
+            throw '`command` must be a String or Function if defined'
         endif
     else
         throw 'Either `command`, `executable_callback`, `command_chain` '
@@ -489,9 +490,13 @@ endfunction
 " Given a buffer and linter, get the command String for the linter.
 " The command_chain key is not supported.
 function! ale#linter#GetCommand(buffer, linter) abort
-    return has_key(a:linter, 'command_callback')
-    \   ? ale#util#GetFunction(a:linter.command_callback)(a:buffer)
+    let l:Command = has_key(a:linter, 'command_callback')
+    \   ? function(a:linter.command_callback)
     \   : a:linter.command
+
+    return type(l:Command) is v:t_func
+    \   ? l:Command(a:buffer)
+    \   : l:Command
 endfunction
 
 " Given a buffer and linter, get the address for connecting to the server.